Geotechnical Instrumentation and Monitoring for the New MetroRail City Project, Perth, Western Australia

P.G. McGough Instrumentation and Monitoring Manager, Leighton Kumagai Joint Venture, Perth M. Williams Special Contracts Manager, Leighton Kumagai Joint Venture, Perth

ABSTRACT: The New MetroRail Project involved a significant number of deep excavations within varying soil types, as well as tunnelling under live railways and heritage buildings. From the onset of the project, significant effort and planning was put into geotechnical instrumentation and monitoring, with over 5200 instruments being installed during the life of the project over a length of less than 3 kilometres. This paper details the initial planning and management process, as well as the contractual requirements, which formed the basis for more instrumentation as the project progressed. Specific project requirements such as compensation grouting under buildings and tunnelling under live railways at depths of less than one tunnel diameter required specific planning measures and additional detailed monitoring which is discussed herein. A large number of automated instruments were used to ensure cost effective and safe collection of data. The types of instruments used on the project are discussed in detail with respect to their applicability, accuracy, reliability, repeatability and cost effectiveness. Examples are presented to illustrate the above points as well as highlight operational issues learnt. The process of data collection, management and reporting is also discussed. With construction taking place in a variety of ground conditions ranging from very soft alluvial silts and reclaimed fill to medium dense alluvial sands and stiff clays a number of distinct response issues were observed by the monitoring. The lessons learnt from three years of continuous monitoring of ground and building movements, groundwater movements, and instrument vibrations are discussed with respect to this project and future projects in Perth within similar geotechnical environments. Detailed examples of ground, sheet pile and wall movements and strut loads with respect to excavation design are presented, along with examples of the exceptionally low volume loss from TBM operation, and resulting building responses to ground movement. An empirical method for predicting ground settlement due to sheet pile extraction is also presented. Examples of ground vibrations induced by sheet piling, construction activities and tunnelling are presented.

1 INTRODUCTION

The minimum required instrumentation for the project was specified in the contract documents referred to as the Scope of Works and Technical Criteria (SWTC), which became the guiding document for tendering purposes and initial estimation. To address the definition of purpose for monitoring, a Building Protection Management Plan was created by Leighton Kumagai Joint Venture (LKJV). The overall purpose of LKJV’s approach to instrumentation, monitoring and building protection was summarised in the Management Plan as follows:

“ to identify the controls to be implemented to ensure personal safety (construction and public), and verify design predictions to prevent damage to buildings, services and civil infrastructure as a result of LKJV construction activities.” [From LKJV’s “Building Protection Management Plan”]

Appropriate management methods were also created and put in place to handle the possible influences of construction activities due to the soft Perth soils. This included selecting “fit-for-purpose” instrumentation that was able to be monitored safely, whilst still providing accurate and timely feedback about construction progress. In addition to working in, with and around the construction personnel, a key criteria was to minimise disruption to pedestrians, traffic flows, and retail business in the CBD.

2 INITIAL PLANNING AND MANAGEMENT PROCESS

2.1 Overview

The need for protection of workers’ safety, property and the environment was foreseen by the Public Transport Authority (PTA) in their tender scope document “Scope of Works and Technical Criteria” (SWTC). These activities included:

• Monitoring the performance of deep excavations with respect to design; • The need for controls to minimise the potential for damage to buildings, services, roads, rails

and bridges from construction activities such as: - demolition; - sheet piling, bored piling or diaphragm wall construction; - tunnelling; - ground improvement activities (jet grouting, soil mixing, compensation grouting); - consolidation from groundwater drawdown.

• Determining a series of baseline condition surveys to objectively determine any damage; • A process for receiving automated alerts if movement criteria were exceeded.

On consideration of the complexity of the final monitoring program, LKJV added the following additional elements to those listed in the SWTC:

• An overall management process to coordinate the activities of design, construction, survey and monitoring crews, with geotechnical and management reviews. A single document (Building Protection Management Plan) was created to bring together the requirements of:

- Geotechnical Interpretive Report; - Ground Settlement, Building Protection and Repair Plan, incorporating Property

Condition Surveys and Building Protection Assessments; - Instrumentation and Monitoring Plan; - Various area-specific Method Statements and Safe Work Methods (i.e., JSA’s); - Feedback from the actual results generated.

• Visual approach to interpretation of monitoring data to allow for quick interpretation by a range of personnel;

• Innovative instruments and monitoring methods such as wireless electrolevel beams and terrestrial photogrammetry driven by safety or minimising disruption to the public;

• Emergency Response procedures as part of the overall risk management plan to cover the event of a massive failure.

Figure 1 outlines the key elements of the building protection and monitoring process.

Investigate exceptions

Construction

and Tunnelling

works

Detailed design

Install instrumentation and monitoring

Condition surveys in zone of influence

Assess the need for building protection

Protection of key structures

Geotechnical investigations

Post construction surveys and repair

Figure 1. The LKJV Building Protection and Monitoring Process

2.2 Damage criteria

After extensive preliminary geotechnical work had been undertaken, modelling of the potential zone of influence of the project works was performed. This determined the width of the potential subsidence zone, based on the predicted design level of induced settlement and TBM face loss.

A key point to note is that although the Ground Settlement, Building Protection and Repair Plan determines a zone of influence based on a designed level of settlement caused by the excavations and the TBM, the actual performance of the TBM was expected to be considerably better than this (i.e., less settlement). This was in demonstrated by the actual TBM operations, where up to 20mm was designed for along William Street, but only around 3-5 mm was observed. The performance of the TBM with respect to design is discussed in more detail later in this paper.

Once the potential zone of influence was determined, a visual Property Condition Report was prepared for each of the following structures along or adjacent to the route of the project:

• 88 buildings, from single storey to BankWest tower; • 5 bridges and footbridges, including the heritage listed Horseshoe Bridge; • Sections of roads and associated furniture along and adjacent to William and Roe Streets; • Around 30 water and sewer services using a CCTV camera.

The design level settlements of the TBM had the potential to cause minor damage to some buildings along the route. An engineering assessment was made to determine whether this potential damage would exceed the limits specified in the PTA’s SWTC. The damage criteria was based on the work of Boscardin and Cording, 1989, which is reproduced as Table 1.

Table 1 - Building Damage Classification

Risk Category

Description of Degree of Damage

Description of Typical Damage and Likely Forms of Repair

Approx. Crack width [mm]

Max Tensile Strain [%]

0 Negligible Hairline Cracks Less than 0.1

Less than 0.05

1 Very Slight

Fine cracks easily treated during normal redecoration. Damage generally restricted to internal wall finishes Perhaps isolated slight fracture in building. Cracks in exterior brickwork visible upon close inspection.

0.1 to 1 0.05 to 0.075

2 Slight

Cracks easily filled. Redecoration probably required. Recurrent cracks can be masked by suitable linings. Exterior cracks visible: some repointing may be required for weather-tightness. Doors and windows may stick slightly.

1 to 5 0.075 to 0.15

3 Moderate

Cracks may require cutting out and patching. Tuck pointing and possibly replacement of a small amount of exterior brickwork may be required. Doors and windows sticking. Services may be interrupted. Weathertightness often impaired.

5 to 15 or a number of cracks greater than 3

0.15 to 0.3

4 Severe

Extensive repair involving removal and replacement of sections of walls, especially over doors and windows required. Windows and door frames distorted. Floor slopes noticeably. Walls lean or bulge noticeably. Some loss of bearing in beams. Services disrupted

15 to 25 but also depends on number of cracks

Greater than 0.3

5 Very Severe

Major repair required involving partial or complete reconstruction. Beams lose bearing, walls lean badly and require shoring. Windows broken by distortion. Danger of instability.

Usually greater than 25 but depends on number of cracks

Greater than 0.3

For each property, a Building Protection Assessment was undertaken by Airey Taylor Consulting that considered the predicted maximum damage from the Ground Settlement Plan and the cumulative variation from the initial damage category assessed in the Property Condition Report. The result was the maximum damage category that could be expected. Building protection was required if the “incremental” damage exceeded the following limits:

• For heritage structures – very slight (up to 1mm crack width); • For other structures – slight (up to 5mm crack width).

In addition to compliance with the PTA’s SWTC, a formal Instrumentation and Monitoring Plan was produced to detail the network of devices which would provide feedback for the following:

• Construction management to ensure the safety of deep excavations is maintained; • TBM operators and management to control the various TBM operating parameters; • Geotechnical Manager to ensure the project’s impact on the surrounding natural and built

environments is minimised and within stated limits.

3 KEY AREAS OF MANAGEMENT FOCUS

In addition to the minimum contractually-specified arrays, there were a number of key construction activities that needed specific management requirements:

• Protection of key structures: A number of structures, buildings and services needed special treatment due to their calculated risk category. All other structures were monitored according to the Instrumentation and Monitoring Plan to confirm the validity of the design assumptions.

• Incident and emergency management: With the extensive array of monitoring devices, LKJV needed a documented process to investigate any devices that showed movement “out of tolerance”, plus planning for major high risk events.

These two areas are discussed in more detail in the following sections.

3.1 Protection of key structures

The main structures that needed unique building protection solutions were:

• Underpinning of the Wellington Building • Removal of the Mitchell Façade • Protection of the Horseshoe Bridge arches • Compensation grouting of the buildings under which the TBM passed • Perth Rail Yard, footbridge and station platforms (where tunnelling under the live railways

was at depths of less than one tunnel diameter) • Claisebrook Sewer.

These are each discussed briefly below.

3.1.1 Underpinning of the Wellington Building

The heritage-listed Wellington Building is a “classic piece of turn of the 19th century corner architecture” under which the new station had to be constructed. As part of the permanent station structure, the Wellington Building had an array of tubular steel and grout micropiles drilled from within the basement. A concrete slab was then poured in the basement but not connected to the micropiles. A series of flat jacks were placed between the top of the micropiles and the base of the concrete slab. The slab was then clamped to the external diaphragm walls, thus forming the roof of the new station. Excavation was then commenced in a top down method under the Wellington Building, with the former footings removed with the first level of excavation, and the weight of the slab and building supported by the micropiles and the diaphragm wall. The excavation was then completed to base slab level and the tubular steel piles were then cut, and tied into the base slab of the station providing an uplift anchor. The weight of the building then sat on the roof slab of the new William Street Underground Station. (WSS)

To monitor the impact of the construction works, around 40 optical prisms were placed around the building and read from robotic theodolites on the Advertising Tower at Perth Station, and the Post Office Building in Forrest Place. This allowed for remote monitoring and interpretation of movements across the building. Being heritage listed, the damage criteria were stricter for the Wellington Building, which meant a much higher density of micropiles were necessary than would be required on a purely structural basis. Additional manual monitoring such as roof and building levelling, tilt monitoring and retro target surveying was undertaken to enhance the automated monitoring.

Figure 2 - Wellington Building, and Excavation of Exterior Brick Wall of Building Prior to Tieing Basement Slab and Capping Beam to Diaphragm Wall

3.1.2 Removal of the Mitchell Façade

Only the façade of the Mitchell Building was heritage listed, but it was located very close to the diaphragm wall alignment for the station. This combined with safety concerns over the stability of the façade’s render meant that LKJV sought permission from the Heritage Council to remove the façade to ensure its protection. Permission was granted and the façade was encased in a steel frame and cut into pieces to be stored off site, as illustrated in Figure 3.

Figure 3 - Mitchell’s Building Prior to, and during breaking up into pieces

3.1.3 Protection of the Horseshoe Bridge

LKJV’s first consideration for the Horseshoe Bridge was full underpinning through installation of jet grout columns under the existing footings. However after more detailed analysis of the structure, the potential for differential movement across the structure was still highly probable. It was determined that due to the flexible nature of the steel-framed structure there would be no structural damage, but the façade heritage features (cement render arches) were susceptible to movement and needed to be propped with timber arches to prevent damage.

3.1.4 Compensation grouting of the “Gold Group”

The “Gold Group” buildings (named for their importance to the project) comprise the following buildings facing William Street between Hay and Murray Street Malls: Friendlies Chemist, HBF, Hungry Jack’s/KFC, Walsh’s Building (McDonalds, and other retail tenancies).

The route of the TBM passed either partially or wholly under these buildings, and LKJV’s Building Protection Assessment indicated the need for protection, with a potential design movement of 20mm.

Due to various space and access constraints, LKJV determined the best option was to work collaboratively with Keller Ground Engineering and implement a TAM compensation grouting system. The details of this system are described in more detail in another paper contained herein by Nobes & Williams (2007)

3.1.5 Perth Rail Station tracks and platforms

The TBM passed twice underneath the station and the live railway, which needed to be kept running at all times. Due to the flexibility of ballasted rail, there was no structural problem should TBM settlements reach the design limits, but such settlements may cause two operational issues. Firstly, if tilting of the platform edge increased relative to the track there would be insufficient clearance for the train, and secondly, if excessive cross cant was to occur it may lead to a derailment.

Due to the success of the first stage of tunnelling up William Street (maximum 5mm settlement), it was determined that an observational approach be taken in preference to preventative measures, with defined management methods and actions. Elements of this observational method included:

• Automatic electrolevel beams on the rail tracks; • Automatic tilt meters on the platform faces; • High density of surface, building and rail settlement points; • 24 hour/7 day week survey, with rail safety presence, and direct ring-by-ring contact with the

tunnel shift engineer; • Specific management measures including:

- A purpose-written Method Statement covering survey, interpretation, tunnel operations and rail safety;

- Daily coordination meetings with all parties (management, survey, geotechnical, tunnel, rail and client);

- Web-based access to all monitoring information for all teams; - Emergency scenario workshops.

The close contact with the TBM crew allowed for parameters to be changed on a ring by ring basis on the survey and automatic results presented. The result was that during the passage of the TBM, the maximum final rail movement was limited to less than 10mm.

3.1.6 Claisebrook Sewer

With the footings of the century old, brick lined, Claisebrook Sewer potentially lying within 800mm of tunnel alignment, protective measures were required. After thorough discussions with Water Corporation, it was decided to re-line the inside of the sewer with new plastic piping. In addition to this, LKJV determined that since a subsidence risk was still present during the passage of the TBM due to fragile nature of the sewer, LKJV also temporarily “over-pumped” the sewer when the TBM was within a zone of influence.

3.2 Incident and emergency management

3.2.1 Incident investigations

All instruments had the following three alert levels determined in the Ground Settlement and Building Protection Plan:

• Trigger, set at say, 80% of the “design” level as an early warning; • Design, equal to the predicted movement level; • Allowable, set at say 120% of the “design” level and at which remedial action must be taken.

For all instruments, these alert levels were entered into the instrument database (GIMS). If a level was exceeded, an SMS and email were sent to a nominated group of people to action as appropriate. When alert levels were exceeded, a rigorous process was followed to ensure traceability of all decisions. This process is shown in Figure 4. If the alert was not spurious, or a transient event, a more detailed investigation was initiated to determine whether any changes to design or construction techniques would be necessary.

• Monitoring frequencies were set for each instrument, and one full time person was dedicated to ensuring the instruments being read matched the progress of the construction works. During the peak months, a team of up to 19 people were dedicated to gathering, inputting, reviewing and investigating monitoring data:

3.2.2 Emergency management through desktop scenarios

Although the chance of an excavation or TBM failure (to a level requiring the assistance of emergency services) was remote, as a key part of the LKJV’s risk management approach, a comprehensive emergency management process was implemented. To test our management plan so that it was a “live” document, we undertook a series of scenario workshops both internally and externally to LKJV.

On 1 December 2005, around 40 representatives from LKJV, Leighton Contractors, Leighton Holdings, New MetroRail (client), Public Transport Authority (operations and infrastructure), City of Perth, Fire & Emergency Services Authority, Police, Worksafe, Western Power, Alinta Gas, Water Corporation, Telstra and Main Roads attended a workshop focussing on the bored tunnel section up William Street. One of the key findings to come from the scenario workshops was that of the role of the Hazard Management Authorities (HMAs) and how to use the existing Memoranda of Understandings between the HMAs and the various government and private agencies.

Another workshop was held on 15 March 2006 with a similar range of external parties, but with more attendance from railway operations personnel, which was the focus of the day. Also a number of internal scenario sessions were held with teams from survey, geotechnical, tunnel and rail to ensure coordination of activities and communication. We also checked that our communication protocols were consistent with Leighton Contractors national approach to Crisis Management, and sought feedback from Leighton Holdings on lessons learnt from recent crisis management activities (Lane Cove Tunnel). Feedback from all sessions was used to make our procedures as user friendly as possible. The aim was to ensure people knew what to do if something escalates from an incident to an emergency.

A Building Access Checklist was also obtained for every property, which LKJV could use to raise an alarm in the case of an emergency. Since LKJV’s monitoring and/or tunnelling teams will probably be the first to know of any incident, we determined that having this information on hand was prudent.

BUILDING AND MONITORING INCIDENT FLOWCHART

NEW METRORAIL CITY PROJECT

Incident occurs1

Is investigation required?

2

Conduct preliminary investigation

5

Is further action required?

6

Complete Incident Form to initiate

AMBER warning

9

Undertake detailed investigation and

formal risk assessment

11

Can incident be resolved?

13

Initiate RED alert via Incident Form

14

Undertake repairs19

Seek authorisation for repairs

18

Repairsrequired?

17

No further action(Update register if

required)

3No

Yes

No

Yes

Record Incident on register and review

details

4

Close out incident21

No

Final inspection and sign off

20

No

Yes

Investigation considerations1. Notification to Area Manager2. Safety of personnel3. Structural integrity of building, infrastructure, or service4. Review of predicted settlement and construction impact5. Quantification of damage6. Review protection works to determine adequacy7. Undertake condition survey to determine extent of damage8. Undertake additional monitoring (eg survey) to quantity and monitor further damage9. Complete risk assessment10. Review of incident impact on both temporary and permanent works design and construction

Action considerations1. Increase monitoring2. Continuous monitoring3. Review construction techniques and equipment4. Review emergency procedures5. Review geotechnical control limits6. Determine whether amber warning or red alert required7. Stop work where required8. Determine urgency of repair work

ConsiderationsEstablish whether incident is legitimate

Considerations1. Identify scope of repair work2. Establish programme for repair work3. Obtain quotes4. Advise PTA5. Advise Insurers6. Obtain property owner/representative approval to do work

Considerations1. Notification to Area Manager2. Safety of personnel3. Structural integrity of building/infrastructure/service4. New occurrence or sudden change in trend5. Compare to existing condition, historical monitoring/reports and any background data 6. Review of recorded levels against control levels7. Visit to location and visual inspection8. Estimate of damage9. Record of construction work being undertaken at time of incident

Point of Contact (PC) Primary Contact Alternative ContactBuiding Incident Matt Williams Kate StoneMonitoring Incident Peter McGough Franco RoselliInfrastructure/Services Incident Michael Wallis Relevant Area Manager

Form W1114-CS-4018

Form W11140-CS-4019

Notify PTA (& insurer) immediately after initiating amber

warning

10

Verify short term remedial action

closed out

12

Verify long term remedial action

closed out

16

Notify PTA (& insurer) immediately after initiating red alert

15

Notify PTA of close out

22

Form W1114-CS-4019Form W1114-CS-4018

Considerations1. Complete "During-construction property condition survey"2. Issue copy of survey and incident report to PTA and obtain property owner/representative sign off.

Yes

PC

PC

Site assessment by GM to agree and implement

action plan

7

Yes - URGENT

PC

PC/GM

GM/PC/AM

GM/AM

GM/DM/CM

PD/CM/GM

CM/PC

CM

CM/PC

SCM/PC

SCM

PD/CM/GM

GM/PC

Special Response TeamSpecial Contracts Manager/NomineeArea Manager/NomineeGeotechnical Manager/NomineeLKJV geotechnical/monitoring repLKJV Subontractor respresentativePTA Representative

If available:Construction ManagerAssistant Construction ManagerDesign Manager/NomineeProject Director

Are only minorrepairs required?

8

No

Yes

LegendPC Point of ContactIM I & M ManagerPD Project DirectorCM Construction ManagerAM Area ManagerGM Geotechnical ManagerDM Design Manager

BUILDING INCIDENT RESPONSECONTACT DETAILS

LKJV MANAGEMENT CONTACTS TELEPHONE MOBILE

Rob Wallwork Project Director 9424 5604 0411 259 451

Tony Cariss Construction Manager 9424 5515 0419 932 132

K. Akabane Ass’t Construction Mgr 9424 5596 0421 404 984

Kate Stone Community Relations Mgr 9424 5588 0422 001 037

F. Aikawa Design Manager 9424 5563 0422 246 067

Simon Gegg William Street Station Mgr 9424 5506 0402 898 627

Paul Farris Southern Area Manager 9424 5631 0422 001 235

Ashley Warner Perth Rail Yard Manager 9228 4942 0421 144 469

LKJV TUNNELLING CONTACTS TELEPHONE MOBILE

Henry Yamazaki Tunnel Manager 9424 5654 0422 593 780

Frank Hannagan Tunnel Superintendent 0421 053 317

Frank Bonte General Foreman 0421 053 313

S. Shigemura Senior Engineer 9424 5653 0422 653 574

M. Oshima Senior Engineer 9424 5691 0413 197 300

Andrew Shepherd Shift Engineer – Tunnel 9424 5651 0411 659 546

T. Watanabe Shift Engineer – Tunnel 9424 5651 0431 120 366

Tom Jones Shift Engineer – Tunnel 9424 5639 0422 001 021

TBM Direct Line 9202 1485

LKJV MONITORING & GEOTECHNICAL CONTACTS TELEPHONE MOBILE

Peter McGough Instrumentation and Monitoring Manager

9424 5519 0421 053 351

Oskar Sigl Geotechnical Manager 9424 5514Intern’l:

0411 659 549+65 9735 2522

Marc Woodward Geotech Manager (alt) 9347 0000 0417 911 131

Barry Hackett Building Protection Eng. 9424 5511 0421 053 337

LKJV RAIL CONTACTS TELEPHONE MOBILE

Peter Rosenbauer Senior Project Eng’r - Rail 9424 5509 0402 894 801

Vasil Calcan Senior Rail Safety Officer 0421 635 8491

Peter Russell Rail Safety Officer 0407 193 915

John Welch Rail Safety Coordinator 9424 5541 0421 711 303

FUGRO CONTACTS (INSTRUMENTATION & MONITORING) TELEPHONE MOBILE

Fugro Monitoring Phone 9424 5617 0439 930 927

Ritchie Mulholland Chief Monitoring Surveyor 9424 5617Home:

0417 611 2959302 6256

Kent Wheeler Monitoring Surveyor 9424 5584 0400 980 060

PTA CONTACTS TELEPHONE MOBILE

Richard Mann Project Director 9326 2536 0419 964 209

Eric Hudson-Smith Geotechnical Manager 9326 2060 0419 988 861

Jock Henderson Special Projects Manager 9326 2093 0419 915 408

INSURANCE CONTACTS TELEPHONE MOBILE

Bob Perry Marsh Ltd 9421 5666 0414 307 247

EMERGENCY CONTACTS TELEPHONE TELEPHONE

PTA Urban Train Control 9326 2214

Main Roads Traffic Operations Centre 9428 2222

Fire and Emergency Services (FESA) 000 1300 1300 39

State Emergency Services (SES) 9277 0555

FESA and SES Operations Centre 9323 9333 9323 9322

WA Police 000 9222 1111

Russell Armstrong (Incident ManagementUnit and LEMC)

9222 1694 9222 1958

Ambulance 000

Bill Thompson 0415 428 617

Worksafe 9327 8777 1800 678 198

City of Perth 9461 3333

Police Post at City of Perth 9325 6000

Bill Strong (LEMC) 9461 5836 0418 947 908

Sadak Hamid 9461 3885 0417 977 101

Transperth 131 608 9325 2277

Alinta 131 352

Amcom 1800 222 019

Optus 131 344

Telstra 132 203

Water Corporation 131 375

George Basanovic 9386 4952 0417 180 677

Western Power (generation) 131 351

Shane Duryea 9427 4257 0407 445 076

Synergy (retail)

Business Faults 131 354

Residential Faults 131 353

Point of ContactPrimary Secondary

Building Incident Peter McGough Kate StoneMonitoring Incident Peter McGough FugroInfrastructure / Mike Wallis Area ManagerServices Incident

Figure 4 - Incident Notification and Investigation Process

4 INSTRUMENTATION AND MONITORING

4.1 Instrumentation Quantities

A total of 5205 instrumentation points were installed on the New MetroRail Project to monitor the influence of excavation, tunnelling, piling and dewatering activities. The instrumentation types, and quantities installed over the life of the project are summarised in the following table.

Table 2 – Instrument Types and Quantities

Instrument Type Quantity Installed Surface Settlement Pin – SSP-1 1021 Surface Settlement Retro – SSP- 2 451 Bored Settlement Point – SSP- 3 559 Deep Settlement Point – SSP- 4 19 Building Settlement Point - BSPB 449 Building Settlement Retro - BSPR 1403 Building Settlement Prism - BSPP 285 Tilt Meter, Manual - TILTM 54 Tilt Meter, Automatic - TILTA 33 Crack Meters – CM 82 Electro Level Beams - ELB 150 Strain Gauges – SG 174 Vibration Sensor - VS 12 Inclinometers - INCL 64 Extensometers, Magnetic - EXTM 187 Extensometers, Rod - EXTM 25 Vibrating Wire Piezometers - VWPZ 91 Open Hole Piezometers - OHPZ 146 5205

In addition to the above, a further 180 recharge and dewatering bores were drilled on the project, most of which were also regularly monitored for water levels.

The instrumentation density installed on the project was considered to be high, with densities being consistently higher than minimum specifications, however a large proportion of the manual settlement points (SSP-1 and SSP-3) required replacement and thus approximately 800-1000 of this number was likely to have been a replacement for points damaged by the construction process. Despite the high quantity of instrumentation, costs for instrumentation and monitoring including drilling remained very low at approximately 3-4% of the tender price.

4.2 Instrumentation Types

The 18 types of instruments used on the project could be grouped into 7 functional types as follows:

• Vertical Ground Movement • Lateral Ground Movement • Building Movement • Building Tilt • Structural Response • Vibration • Groundwater Movement

The instruments used in each of the functional groups, their suitability for purpose, reliability, accuracy, repeatability, and cost effectiveness are discussed in detail in the following sections:

4.2.1 Vertical Ground Movement

Ground Movement, (settlement and heave) was measured using the following instruments:

• Settlement Pins (SSP-1), [survey nails and bridge spikes installed in roads, bridges and footpaths]

• Settlement Points (SSP-3), [steel reinforcing rods grouted 800mm deep into a borehole] • Deep Settlement Points (SSP-4), [steel reinforcing rods grouted into borehole approximately

1.5m above services] • Rod Extensometers (EXTR), • Magnet Extensometers (EXTM) • Reflective Photogrammetry Targets • Electrolevel Beams • Retro Targets

Settlement pins, settlement points and reference head on the rod extensometers were all measured by means of digital levelling using a Leica DNA-10 Digital Level and Barcode Staff. Typically traverses of up to several hundred metres were undertaken without control points. A misclosure limit of 3mm was used as the acceptance criteria for these traverses. The repeatability of surveys was within +/- 1.5mm of the true or mean level as illustrated by Figure 5, which was a point sufficiently away from all excavation and tunnelling that no settlement occurred. Vibration from pedestrian traffic and machinery was a common problem, due to the city location, with shaking of the digital level visible through the optical sight. This vibration occasionally resulted in gross errors, which were much greater than +/- 1.5mm.

Raw survey data downloaded from field was adjusted via the least squares method. Data was then “dumped” into excel spreadsheets for verification. Verified data was then exported to GIMS database for permanent record. Contouring or cross sectioning of data was then undertaken. Whilst apparently tedious, the above method enabled easy verification and manipulation of large quantities of data without impacting on the integrity of the raw database. Typical examples of sectional and contoured output are shown in Figure 6 and Figure 7.

The deep settlement points drilled into the ground (type SSP-3 and SSP-4) typically showed less fluctuations than the smaller survey pins and spikes (type SSP-1) hammered into the ground and thus were considered more reliable. The results on the project indicated that there was no discernible difference in the total measured movement between points installed through road pavements (type SSP-3) and those installed at the surface of the road (type SSP-1), inferring that the road base was flexible enough to reflect the ground movements occurring at subgrade level, even where asphalt thicknesses of 100-200mm were found along William Street.

An innovative drilling method was used to install settlement points in areas where coring of the upper materials was not required. Drilling via vacuum extraction was used to install SSP-3’s and SSP-4’s in many areas. The method simply involved the use of a pipe connected to suction truck, which vacuumed up the sands, thus forming a hole, as illustrated in Figure 8 and Figure 9. The method is normally used in Perth to locate and expose buried services, but we found it was ideally suited to our purpose of forming shallow holes in a very quick and cost effective manner with no preparation or clean up required. The shallow holes were formed within a few minutes, with the installation of the grouted steel settlement rods occurring immediately after hole drilling, thus the whole process was typically complete in 10-15 minutes.

13.795

13.805

13.815

26-Oct-04

25-Dec-04

23-Feb-05

24-Apr-05

23-Jun-05

22-Aug-05

21-Oct-05

20-Dec-05

18-Feb-06

19-Apr-06

19-Jun-06

18-Aug-06

17-Oct-06

16-Dec-06

Red

uced

Lev

el (m

AH

D)

SSP_0533 Reduced Level

Figure 5 – Example of Repeatability of Settlement Point

Ground Movement Profile Due to Tunnel 2 Excavation - CH 440 PMup(Chainage: 440 PMup +/- 10m, Tunnel 1, Vs = 0.00% Tunnel 2, Vs = 0.60%)

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

-50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0

Chainage (m)

Settl

emen

t (m

m)

3/08/2006 8:004/08/2006 8:005/08/2006 8:006/08/2006 8:00Design Volume Loss Curve

K=0.45Vloss = 0.70% (320m radius of curvature)(VLOSS = 0.60% if straight)

Tunnel 2 Cutter Face at CH 450 approx, 2/8/06 18:00Tunnel 2 Cutter Face at CH 430 approx, 4/8/06 03:00

Figure 6 –Example Cross Sectional Display of Tunnel Settlement with Time

Figure 7 –Example Contoured Output of Settlement Data Around Major Excavation

Figure 8 – Vacuum Extraction Drilling Figure 9 – Vacuum Extraction Unit

Rod extensometers used on the project were the multiple head grouted anchor type supplied by Slope Indicator Company (SINCO). The heads were typically grouted 1.5 and 4.5 metres above the tunnel

crown, and during tunnel passage the differential movement of the rods relative to the fixed head was measured manually with micrometer. The results obtained were consistent with tunnel activities and show that micrometer repeatability was approximately +/- 0.25mm, as illustrated in Figure 10, but calculated total movements were limited by the head levelling repeatability of +/- 1.5mm.

The installation of the rod extensometers was a prescribed requirement on the project, with the benefit of the installed rod extensometers being questionable as the results confirmed the knowledge that relatively greater settlements occur at depth than at the surface. The density of the extensometers installed (1 per 200m) served no other benefit than to confirm this fact, with the higher density of surface monitoring providing a better warning of face loss or heave.

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Figure 10 - Typical Example of Rod Extensometer Output Data

Figure 11 - Typical Example of Magnet Extensometer Data

Magnet extensometers were used adjacent to excavations in preference to rod extensometers. The type of magnets used on the project consisted of magnetic strips attached to corrugated plastic pipe, which slid over standard inclinometer piping. The magnets were installed at intervals of 3-5m down the inclinometer hole. The inclinometer and magnet were then grouted into place, initial readings taken; a period of equalisation (~30 days) was then foregone before secondary readings were taken. Readings were taken via lowering a probe down the centre of the inclinometer pipe until it reaches the bottom magnet position. The tape is then pulled up and as it passes each magnet, two beeps are heard; the depth at which the second beep is heard is recorded for each magnet. The method is prone to gross errors. The repeatability of the measurements is approximately +/- 5mm as illustrated in Figure 11, with gross movements with depth clearly visible once excavation induced settlement commences. The settlement of the top of the inclinometer was also checked via regular levelling and compared to the observed results. The magnet extensometers were considered highly suitable for the intended purpose of measuring large movements where accuracies of +/- 5mm were acceptable. Magnet extensometers provided a cost effective solution without the need for multiple boreholes or expensive rod extensometers, or alternatively they provided additional information at minimal cost from an existing planned inclinometer. Experience from this project would suggest that at least 5 readings be taken to establish an average baseline value before any excavation or external loading commences.

Settlement monitoring was also undertaken with retro reflective targets located on rail tracks or survey spikes in areas where access for regular levelling was not possible. This method of survey was undertaken using Leica Total Stations and was slightly less repeatable than digital levelling, with higher degrees of scatter in the measured results. Repeatability using this method was in the range of +/-2mm. This reduced repeatability is likely to be a result of human error as the surveyor focuses on the centre of the target to get the correct result. As discussed later in the building monitoring section, the effect of one or two face readings is also likely to have impacted on the repeatability of the results obtained from this type levelling.

Due to the need to focus on the target, the resulting retro target survey is slower than compared to digital levelling. However as this method only requires one surveyor for the majority of the survey, the operational costs incurred can be less than or equal to digital levelling in many cases. Experience

on the project indicates that using retro targets for long term settlement monitoring should only be considered where access is limited for level surveys, or where automated instrumentation cannot be installed. In contrast, for short term high density monitoring of restricted access areas, retro targets would provide a cost effective solution as they only cost a few dollars each to supply and install, and the degree of repeatability can be negated by small traverse lengths and high frequencies of monitoring.

Figure 12 - EL Beams installed along centreline of active rail line

Figure 13 - Proximity of Retrieval Box Excavation to Active Rail Line

Automated Electro-Level (EL) Beam monitoring was also used to monitor settlement of the train tracks as excavation and tunnelling occurred in the Perth Rail Station and Perth Rail Yard. EL Beams were required as access to the active rail area was limited with trains operating 18-20 hours per day, and excavation was occurring within 1m of active tracks (Figure 12 and Figure 13), and tunnelling occurred directly below the active train lines of Perth Train Station. Chains of EL beams were used to obtain settlement profiles along the centreline of rail tracks, and transverse movements were also measured every few metres. The ends of each EL beam chain were regularly verified via levelling and settlement profiles adjusted for end settlement if applicable. Some EL Beams were in place for almost 2 years, and despite the vibrations from regular train traffic (every 2-30 minutes), extreme heat, and weather, the EL beams showed no creep effects, with the repeatability of the entire chain remaining in the range +/- 1.0mm of a mean value. A typical settlement profile and the fluctuation in the readings observed over a 6 hour period where no construction activity was occurring is shown in Figure 14, illustrating the high degree of repeatability.

The EL beam results were also consistent with excavation and tunnelling activities, with retro target monitoring undertaken during tunnelling confirming the accuracy of the individual EL Beams as shown in Figure 15, as well as highlighting the immediate response of the ground/rail as the TBM passed underneath the beam shown. The sub millimetre accuracy of individual EL beams was highlighted in their ability to resolve the daily 2mm variation in track height due to thermal effects. As a result of this EL beam monitoring, there was continuous train operation throughout the 3 years of the project, even with excavations within 1m of active trains as illustrated in Figure 13.

An innovative method of settlement monitoring using photogrammetry and auto target recognition software was trialled on the project. Reflective targets mounted on the sides of “Cat’s Eyes” on the road above the tunnel, on kerbs and on buildings, were monitored for movement. The aim of the photogrammetry was to reduce the time the surveyors were spending on William Street, which was a busy one way street through the centre of Perth CBD. By using photogrammetry, thus reducing the survey time on the road, the risk of injury to our surveyors was reduced significantly as normal survey required a moving method of traffic management (cars with flashing arrow boards and surveyors working in front) in order to maintain traffic flow. In addition to the safety risks, the reduced cost of traffic management and survey time was a benefit of this method of monitoring.

Figure 14 - Typical Repeatability of EL Beam Located on the Railway (15min readings over 6 hr period)

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The reflective targets were typically 15-20mm in diameter and glued to the side of the “Cat’s Eyes” as shown in Figure 16. Additional points were also installed on the adjacent kerbs and buildings, as illustrated in Figure 17. Once an initial photo model was generated (from multiple photos), software automatically determined the location and change in movement of each reflective point in subsequent photos, with each model only requiring four control points. The photogrammetry software used was 3DM Calib Cam by Adam Technology, with an example model with automated target points recognised and labelled shown in Figure 18. Typically two photogrammetry surveys per day were run, with greater than 100m of tunnel coverage in each photo model.

There was good correlation with manual level surveys as illustrated in Figure 19 (Note: SSP 3005 = manual level, SSP 2317 – 2319 = Photogrammetry Level), however due to the low levels of tunnel deformation in the study area there was insufficient data to confirm the repeatability of the system relative to levelling. The system proved to be fit for purpose and has numerous applications for monitoring of buildings and structures at low cost. The safety benefits of the system cannot be understated as it significantly reduced the period the surveyors were exposed to life threatening injuries such as being hit by a car. If adopted at the start of a project the quantities of building and settlement monitoring surveys would be reduced significantly thus saving hundreds of thousands of dollars annually to similar projects of this type.

Figure 16 - Reflective Target on Cat’s Eyes Figure 17 - Reflective Targets on Kerbs/Buildings

Figure 18 - Photogrammetry Model with Automatic Target Recognition Generated from Figure 17

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Settlement monitoring was the most time consuming and costly exercise on the project. The cost of a surveyor and assistant was approximately A$1500 per day over 2.5 years (approximately A$500,000 per annum per survey crew), and 2-3 crews were operating at most times throughout the project. In addition to this, daily traffic control at A$1000-A$2000 per day was also required when surveying above the tunnels, and on highly trafficked streets where excavation induced settlement was occurring. Experience shows that substantial cost savings in survey would have been possibly gained in using automated EL beams mounted below footpaths and roads given that each EL beam costs in the order of A$2500-A$3000 for a 3m beam length.

The use of automated instruments would also have reduced the quantity of engineer supervision on the project whilst providing highly desirable continuous information to tunnelling and construction personnel. The density of EL Beam readings would also have benefited the end users, as readings would be spaced at 3-5m intervals rather than the 12-25m centreline spacing than was only possible with manual monitoring.

4.2.2 Lateral Ground Movement

Lateral ground movement was measured primarily through inclinometers installed adjacent excavations and between tunnels. The lateral movement of several sheet piled structures and rail lines was also measured using retro targets.

The inclinometers and casing used on the project were supplied by SINCO and were found to be extremely reliable with approximately 8km of readings (spaced at 0.5m intervals) being undertaken each week, or more impressively approximately 800,000 readings per year totalling over 400km. During the 2.5 year monitoring period, only the wheels and springs required replacement once. Repeatability of measurements in holes up to 40m deep was found to be less than +/-1mm over the 40m, and did not change throughout the project. The results obtained were consistent with expectations, with the development lateral ground movements and ongoing creep consistent with excavation activities.

Given the quantity of readings obtained by monitoring personnel and the high potential for back injury, a simple extension piece which fitted over the quick connect collar of the casing was developed at the start of the project. The purpose of the extension piece was to extend the reading height to approximately waist height (as shown in Figure 20) reducing the need for bending over the hole continuously as is the common procedure (as shown in Figure 21). As a result there were no recorded back injuries or complaints from monitoring personnel over the life of the project despite the millions of readings taken.

Figure 20 - Inclinometer Measurement with Extension Piece to Waist Height

Figure 21 - “Normal” Inclinometer Measurement requiring bending over the borehole

Automated Inclinometers (IPI’s) were also used on the project in high traffic areas where access for periods greater than 5 minutes was not possible, or posed an unacceptable risk to monitoring personnel safety. The IPI’s were used to monitor ground deformations between the two tunnels along William

Street, and in a bus lane adjacent a bridge founded on stone columns. The IPI’s generally performed very well and produced excellent results, and were stable for periods of more than 1 year. The response of individual sensors was excellent, with a repeatability less than +/-0.2mm as illustrated in Figure 22 below, with the overall accuracy of a 24m chain approximately +/- 0.5mm as illustrated in Figure 23. There was a small proportion of sensors that showed minor creep movements, however these were replaced by the supplier under warranty. It should be noted that in Figure 23, the temperature sensors recorded increased temperatures after the tunnel passed which was possibly linked to the exothermic heat generated during curing of the tail void grout.

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Whilst expensive to install, the IPI’s are recommended for where long term monitoring of large excavations is required in developed countries (i.e. cost of manpower is expensive). A typical 30 metre IPI and datalogging system may cost approximately A$20,000-A$25,000 to purchase, however if that instrument is logged every two days over a period of 1 year, the cost of two monitoring personnel to undertake the same manual inclinometer surveys would also cost in the region of A$20,000 or more. Whilst the cost benefits are neutral over 1 year, the benefits lie in the continuous information gained and ability to warn of impending failures at any time. Additional benefits are that construction personnel can have unrestricted site access, allowing continuous traffic/machinery flow above (assuming the instruments are located under 1m of fill), and importantly the IPI’s can be retrieved and re-used at other locations thus reducing the overall cost for longer and larger projects.

The IPI’s were located in highly trafficked areas, and hence restrictions on installation time and area available for drilling were present, so a drilling technique new to Australia; sonic drilling, was utilised. Sonic drilling allowed rapid dry coring of the borehole from the surface, through 100-200mm of asphalt, to depths of approximately 30 metres in one night. The continuous coring was of great benefit in geological logging, whilst the dry drilling method was very beneficial environmentally as no sumps or mud tanks were required to contain wash cuttings, thus also saving valuable clean up time. The machine used was also compact and thus traffic management was confined to two lanes, and the IPI installation was completed in one night. The cost savings compared to traditional rotary methods were substantial. The sonic core method was also used to drill and install SSP-3’s and Rod Extensometers above the tunnel centreline, and to sample jet grout and soil mix columns. The method allowed rapid coring (in the order of a few minutes) through the thick surface asphalt and crushed rock road base into the subgrade, with the machine quickly mobilised to the next drill location in 5-15minutes.

Figure 24 – Sonic Drill Rig in William Street Figure 25 – Sonic Rig Showing Coring Barrel and Catch Tray for Water from Core Barrel

4.2.3 Building Movement

Building movement (settlement and heave) was monitored using the following instruments:

• Building Settlement Points (BSP), [bolts installed into buildings, bridges and structures] • Retro-Reflective Targets (BSPR) • Optical Prisms (BSPP) • Reflective Photogrammetry Targets • Electrolevel Beams

The BSP’s were levelled in the same manner as the SSP’s, using a digital level and barcode staff. The levelling results on the project showed the same degree of repeatability as the SSP’s (+/- 1.5mm).. The bolt used was a standard threaded bolt grouted into a wall, with a hexagonal nut at the end protruding approximately 25-50mm away from the wall. The cost effectiveness of installing specialised bolts could not be justified given that these bolts were unlikely to result in any significantly increased accuracy or repeatability.

The Retro-Reflective Targets on buildings were not consistent instruments, with large variations in readings of up to +/- 3mm. Experience showed that they were not suitable for low frequency background monitoring. The readings were highly dependent on operator skill and also on angle of incidence to the target, thus on larger survey runs where the angle of incidence could be small the reliability would reduce, as illustrated by the last five surveys in the example in Figure 26. The point in this example was on a very large building located more than 2 tunnel diameters from the second tunnel and was considered stable. Where the angle of incidence to the target was large (i.e. operator was facing the target) and the length of survey was small, the degree of accuracy generally improved as illustrated by the surveys during both tunnel runs in Figure 26, where repeatability reduced to +/- 1.5mm, which was in line with levelling. One action, which could not be verified, was whether two face readings of retro targets were used as standard practice. Apparently one face readings were used for points less than 25m from the operator and two face readings were used for greater distances. This non systematic use of one face readings is likely to have resulted in the higher than expected variability shown, as the positive benefits of two face readings are discussed in the following paragraphs.

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Optical survey prisms were installed on building facades and roofs, and monitored from a network of total stations. The automated monitoring showed that repeatability was generally in the range of +/- 1mm given the best conditions, as illustrated by Figure 27. Many factors such as; weather, heat haze, restaurant exhausts, and the angle of incidence also effected the results, but the most pertinent factor in effecting the accuracy and repeatability was the use of “one-face” or “two-face” readings. A total station can read the same point, either as foresight or a backsight, and experience on the project showed that use of only the foresight (one face) prior to 22/5/05, resulted in a high degree of variability as illustrated in the left half of Figure 28. When the average of the foresight and backsight

was used (“two face”), the variability reduced significantly as indicated by the results on the right half of Figure 28. Whilst the degree of repeatability can be good, the examples shown also highlight that many spurious outliers can be obtained and thus high frequencies of monitoring are required to negate these spurious results.

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Electrolevel (EL) Beams were also used inside several buildings on the project. The EL beams were installed on the internal walls of several basements and ground floors, in the roof cavity of another basement, and on the 1st floor slab of another building. The EL beams installed were totally wireless and self contained, running on an internal lithium battery. The EL beams transmitted a radio signal every two minutes to an external wireless repeater, which then amplified and repeated the signals to the project office several hundred metres away. Live results with automated alarming were also available to multiple users on the project network at any one time.

As the EL Beams were located within buildings away from the elements and vibrations, the repeatability was substantially improved when compared to EL beams located on the rail tracks. Repeatability was less than +/- 0.01mm per 3m length (1:300,000), which is excellent when compared to other forms of monitoring. The instruments proved completely reliable with no recorded interruptions during the year of service, with the only disadvantage being the quantity of data received was sometimes too much for the logging computer to handle after a network outage or backup. The instruments resolved tunnel settlements so accurately that instant changes to tunnel parameters could be made, such that tunnel induced settlement under the monitored buildings was contained to almost negligible levels.

The EL Beams used on the project proved to be so sensitive that they were able to pick up the ground vibrations and resultant building movement in Perth from a Magnitude 7.6 earthquake in Indonesia over 5000km away as illustrated in Figure 29 and Figure 31. Shaking and building movement was recorded on all EL Beams located within the buildings, with the time and duration of movement corresponding exactly to the time and duration of movement recorded at the Mundaring Geophysical Observatory just outside of Perth. The comparison of results is shown in Figure 30 and Figure 31. [Please note that the geophysical observations are in Universal Time Clock (UTC) whilst the EL Beam data is in local time, which is 8 ahead of UTC {17:00 UTC 27/1/06 = 01:00 Local 28/1/06}]. This level of sensitivity further confirmed the suitability of these instruments for the purpose of building monitoring.

Figure 29 - Source Location of Earthquake Measured by EL Beams

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Figure 30 - Response of Individual EL Beam to Earthquake >5000km Away

Figure 31 - Matching Earthquake Response at Government Geophysical Recording Station

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Optical prisms are considered to be the most cost effective solution to long and short term monitoring and are favoured ahead of all other types of monitoring. Optical prisms can be purchased for approximately A$150 each, and automated total station rented for A$2000-A$3000 per month. Therefore an example group of 4-8 buildings could be sufficiently covered by 2 total stations and approximately 100 prisms for an upfront cost of A$15,000 and approximately A$5000 per month. Assuming a tunnelling under the buildings of interest scenario, a daily survey of the same buildings for 2x1 months, and weekly survey for the remainder of a year using level points and prisms would cost approximately $150,000. The same automated survey would cost approximately $75,000 for the same period. This scenario repeated many times along a large excavation or tunnel project has the potential for substantial cost savings whilst increasing safety, reliability and accuracy of measurement.

EL beams are also potentially cheaper than most other monitoring options if the project is long, or if they can be re-used elsewhere on a project. For example, a group of 4-8 buildings (say 150m long by 40m wide) could be instrumented around the base perimeter for approximately $400,000. Whilst this is a large up front cost and potentially larger than most projects would be willing to consider, it should be noted that there are no ongoing running costs, bar a monthly or weekly control survey to check the level of end points. Thus where monitoring of more than a year is required, EL beams could become very cost effective as a single installation, or alternatively as the EL beams are wireless and cable free they can be simply moved to new locations and installed as required, negating the need for regular survey thus reducing manpower costs substantially. This type of saving could only be achieved if adequate planning is introduced prior to construction.

4.2.4 Building Tilt

Building tilt in response to excavation and tunnelling was monitored using both manual and automated tilt meters. The manual tilt meters were supplied by SINCO and consisted of a brass plaque mounted on a wall, upon which a portable tiltmeter is placed to take a manual reading. Repeatability of the tiltmeter was in the range of +/- 0.025 degrees (1:3600) as illustrated in Figure 32 where this instrument was located on a building not subject to any tunnel influences. The manual tiltmeters were found to be very fit for purpose, able to measure large ranges of tilt, highly durable and not subject to thermal effects, with operator error the only potential downside as illustrated in the example results shown in Figure 33 where a rail mast was tilting in response to excavation. The manual tiltmeters were also able to be re-used with no detrimental effects. Typically 2-4 tiltmeters were installed per building.

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Figure 33 – Example of Distinct Tilt Meter Result

Automated tilt meters were also used on the project. The tilt meters were cable free and wireless as per the EL Beams. Two types of automated tiltmeters were used on the project. The first type was the “off the shelf” wireless tiltmeter supplied by ITM Soil Instruments, and the second was fabricated in house using the sensor and transmitter from a wireless EL Beam as shown in Figure 34.

The automated tiltmeters were installed on buildings in close proximity to tunnelling, with typically 2-3 installed per building. The automated tiltmeters were used for short tern monitoring as the tunnel passed, and were leap frogged from building to building as the need arose. The results from the automated monitoring varied, with some buildings and tiltmeters being subject to greater extremes of heat and wind than others, and as a result large daily and monthly variations in building tilt were discernible as illustrated in Figure 35. Where extremes of heating and weather were less pronounced, heating effects were still observable but were generally minor in comparison to the observable effects from tunnelling or excavation as illustrated in Figure 36 where the tilt of the building in response to tunnelling can be clearly discerned from the background daily thermal fluctuations.

The automated tilt meters were considered highly accurate with similar levels of repeatability to the EL Beams given a sheltered environment, however in the exposed conditions repeatability was still in the order of +/-0.02mm/m (1:50,000), which is approximately 10 times more accurate than manual tilt monitoring. With this level of repeatability, the very minor building tilt of 0.05mm/m (1:20,000) shown in Figure 36 is clearly discernible. Given this example, the benefit of automated monitoring on buildings close to excavation and tunnelling cannot be understated, especially when teamed with optical prisms as shown in Figure 34.

Gross Operator

Error

Measured Inclination

Change in Inclination

Figure 34 - Typical Automated Tilt Meter

Figure 35 – Example of Daily and Weekly Variations in Building Tilt

Optical Prism

Automated Tilt Meter

Figure 36 – Example of Building Tilt in Response to Tunnelling

4.2.5 Structural Response

The response of buildings and major excavations to the forces imposed on them from ground movement and excavation was monitored in many ways.

The internal movement of buildings (hogging and sagging) was measured via EL Beams, Optical Prisms, and Crackmeters. The EL beams and Optical Prisms have been described in previous sections and experience on the project has shown that the EL Beams are most suited to determination of building deformation. Three types of crack meters were used on the project; a simple tell tale crack meter, crack pins, and an optical crackmeter.

The tell tale crack meter is a simple plastic scale glued over a crack as per Figure 37. This device is very coarse in its measurement, with resolution in the order of 0.5mm due to the 1mm scale. The repeatability and resolution of the instrument was improved on the project via reading the edge points of the cross hairs and averaging the readings instead of trying to read the cross hair location itself. The instrument is unable to determine the width of the crack prior to installation and procedures should be in place to ensure all crack widths are measured prior to installation. Due to the poor resolution, subtle building responses could not be determined and as such this method of measurement was not suitable for most building monitoring. The only benefit of this method of measurement was that it could be read through a total station, binoculars or zoom lens of a camera, thus was suited for inaccessible locations where other forms of manual measurement could not be undertaken.

The use of two survey pins or bolts drilled either side of a crack and this distance between the pins measured using vernier callipers was another method of crack measurement used on the project. The vernier callipers were accurate to less than 0.1mm and repeatability was similar. The use of survey pins was preferable to tell-tale crack meters where regular access was possible.

A third more desirable method of crack measurement was adopted later in the project. This method involved the use of a portable optical microscope Figure 38 that contained a graduated optical scale in

the field of view. The optical crackmeter allowed for direct measurement of crack widths up to 2mm with repeatability of +/-0.05mm. which was substantially more accurate than a tell tale crackmeter. The measurement is simple and involves the marking a reference line across the crack, which is then viewed and measured using the scale in the field of view.

Figure 37 – Telltale Crack Meter Figure 38 – Optical Crack Meter

The structural response of struts, diaphragm walls and sheet piles to loading and excavation was also determined on the projects via the use of strain gauges, retro targets and inclinometers.

Approximately 5% of the struts on the project were instrumented using spot welded vibrating wire strain gauges (VWSG’s). The gauges were installed in sections so that comparative results of loading at each stage of excavation could be achieved. The gauges were installed in groups of four on each strut so that simple averaging of loads could be achieved. The strain gauges were thermally calibrated according to the procedure described by McGough, 2007 to ensure that the effect of gauge expansion was accounted for, and the loads induced by excavation and thermal strut expansion could be clearly defined. Spot welded strain gauges were used to ensure that there was complete integrity with the steel strut. The VWSG’s proved to be highly reliable, with many gauges remaining in place for over a year whilst exposed to the elements and strut temperatures of 0-70OC. The use of VWSG’s was preferable to other strain gauges as no signal loss occurred with distance, as hundreds of meters of cable was required in some locations to reach the automated dataloggers. All VWSG’s were logged continuously, and alarmed. The results obtained from the strut measurements were consistent with design expectations. Examples of strut load response to excavation are shown later in this paper. Field comparisons of VWSG and spot welded resistance strain gauges (RSG) were also undertaken in William Street Station and confirmed the validity of the VWSG results. Further details are of these comparisons are described in McGough (2007).

The deflection of sheet piles in response to excavation was measured using retro targets. The retro targets were selected for this type of structural monitoring due to their ease of installation and cost effectiveness. The retro’s were stuck on the sheet piles very soon after excavation was completed for each stage. Regular surveys were then undertaken to confirm the sheet pile response to excavation and strut placement. The results were typically consistent with design expectations and the +/- 2-3mm repeatability was sufficient for the purpose. The retro’s were able to highlight where significant movements had occurred, generally confirming additional deflections in areas of crane or machine loading. These results were compared with inclinometer observations in the soils immediately behind the sheet piles and with the strut load measurements and were found to be consistent. Retro measurements were also used on the inside of the diaphragm walls at William Street Station to monitor the deflection in the wall in response to excavation.

Whilst the retro targets provided a means of measuring the relative response to excavation, they were of limited value beyond the excavation stage as the permanent works covered them as it progressed. In addition to this limitation, a large proportion of movement was likely to have occurred before they were installed, thus they could not be a true comparison with design estimates. Experience on the project would recommend that retro targets are most suited for measurement of deflection at the top of sheet piles and that a number of inclinometers should be installed with the sheet piles at the time of

driving. Regular prism surveys of the top of the inclinometer pipe should also be undertaken to confirm whether lateral movement is occurring at the toe of the sheet pile.

Installation of inclinometers in diaphragm walls was undertaken in conjunction with wall construction to measure the structural response of the diaphragm walls at William Street Station. The inclinometer casing was installed with the reinforcing cage for diaphragm walls, and thus formed an integral part of the wall. Whilst this method was satisfactory, it was less than perfect, as the top of the inclinometer was not surveyed regularly enough for deflection due to construction constraints and thus it could not be confirmed whether the base of the wall was moving laterally. Hence it was generally assumed that lateral deflection was not occurring, and that the base of the diaphragm wall was fixed. Damage to the top of the inclinometers also occurred on many occasions as jack hammering to expose the reinforcing for the roof slab connection occurred, thus preventing regular checking of the top levels. Despite the above limitations, the inclinometers installed in the walls typically showed wall deflections much less than design, with these low levels of wall deflection confirmed by similar low values in the strain gauges and retro targets. It should also be noted that diaphragm walls exhibit very large heat of hydration on curing (up to 70-80 0C), and as such the stability of the inclinometer casing under these temperature loads was checked as assessed as suitable.

4.2.6 Vibration

The vibrations and noise from sheet pile installation were predicted to be a major cause of concern for the project given the large amount of sheet piling (>2km of piled walls up to 24m deep) and the confined nature of the site within the CBD. Given these concerns a number of geophones were installed in the ground and in buildings surrounding the major excavations. A total of 7 Instantel Minimate blast monitors and triaxial geophones were utilised at any one time around the project. The monitors were self contained, running either on mains power or battery. The monitors were completely programmable with recording of peaks, individual events, or waveforms possible. Trigger values for recording could also be programmed via computer or directly at the unit.

The monitors and geophones proved entirely reliable, except when exposed to damp environments where condensation occurred. Geophones located in damp areas or within boreholes often malfunctioned in the presence of condensation and thus required thorough “drying out” before they could be re-used. Their calibration and suitability for re-use was re-checked versus a reference geophone which was kept in the office for this purpose. Whilst the instruments used were capable of remote download, this function was not used, and manual download of the instruments on every 1-3 days was undertaken.

Construction induced vibrations from machinery were easily determined from inspection of the output, either as a x-y scatter graph of a trigger event, or inspection of a waveform as shown in Figure 39 and Figure 40. Clusters of vibration typically occurred around a dominant frequency where there was a mechanically induced vibration, and inspection of the waveform with time generally confirmed that the waveform was of a uniform nature as shown in Figure 39, which illustrates the ground vibration in response to sheet piling. For other events, there were typically large thuds on a waveform graph and they were spatially non descript on the x-y scatter graph as illustrated in Figure 40, which represents the measured response to closing of a borehole cover.

Monitoring of vibration on the project revealed that vibrations from construction activities were below threshold levels at all times outside of the site boundaries. It was found that vibrations from sheet piling installation were typically much less than those at sheet pile removal stage.

Event Report

Printed: M ay 1, 2007 (V 8.01 - 8.01) Form at Copyrighted 1996-2004 Instantel Inc.

Date/Tim eTrigger SourceRangeRecord Tim eJob Num ber:

Long at 10:40:11 July 20, 2004Geo: 3.00 m m /sGeo :31.7 m m /s2.0 sec at 1024 sps1

Serial Num berBattery LevelCalibrationFile Nam e

BE9498 V 7.1-4.35 M iniM ate Plus6.4 VoltsM ay 28, 2004 by Instantel Inc.K498A7B1.M Z0

NotesLocation: Launch Box AreaClient: LKJV/PTAUser Nam e:General: VS-148-002 - located in BH2022

Extended NotesCom bo M ode July 20, 2004 09:58:55BH2022 located beside buslane access from W illiam Street.

Post Event Notes

PPVPPV (Ponderated)PPVZC FreqTim e (Rel. to Trig)Peak AccelerationPeak Displacem entSensorcheck

Tran

3.021.5960.657

-0.2080.161

0.00668Disabled

Vert

1.941.0456.739

1.9320.126

0.00623Disabled

Long

3.842.1862.757

0.7340.174

0.00912Disabled

m m /sm m /sdBHzsecgm m

Peak Vector Sum 4.64 m m /s at 0.853 sec

USBM RI8507 And OSM RE

Velocity (mm/s)

Frequency (Hz)

1 2 5 10 20 50 1001

2

5

10

20

50

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200254

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+

+

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+ ++ ++++ +++

+ ++ ++++ ++ ++ +++++

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0.00.0 1.0 2.0

Trigger =

0.0Long

0.0Vert

0.0Tran

Tim e Scale: 0.20 sec/div Am plitude Scale: Geo: 1.000 m m /s/div

Event Report

Printed: M ay 1, 2007 (V 8.01 - 8.01) Form at Copyrighted 1996-2004 Instantel Inc.

Date/Tim eTrigger SourceRangeRecord Tim eJob Num ber:

Vert at 09:59:18 July 20, 2004Geo: 3.00 m m /sGeo :31.7 m m /s2.0 sec at 1024 sps1

Serial Num berBattery LevelCalibrationFile Nam e

BE9498 V 7.1-4.35 M iniM ate Plus6.4 VoltsM ay 28, 2004 by Instantel Inc.K498A7AZ.QU0

NotesLocation: Launch Box AreaClient: LKJV/PTAUser Nam e:G eneral: VS-148-002 - located in BH2022

Extended NotesCom bo M ode July 20, 2004 09:58:55BH2022 located beside buslane access from W illiam Street.

Post Event Notes

PPVPPV (Ponderated)PPVZC FreqTim e (Rel. to Trig)Peak AccelerationPeak Displacem entSensorcheck

Tran

12.33.4072.8>1001.5510.9380.0307

Disabled

Vert

21.84.9577.8<1.01.5472.200.615

Disabled

Long

14.88.7374.447

0.0201.04

0.0857Disabled

m m /sm m /sdBHzsecgm m

Peak Vector Sum 24.6 m m /s at 1.547 sec

USBM RI8507 And OSM RE

Velocity (mm/s)

Frequency (Hz)

1 2 5 10 20 50 1001

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Figure 39 – Typical Ground Vibration Response to Piling

Figure 40 – Typical Ground Vibration Response to Non Mechanical Disturbance

4.2.7 Groundwater Monitoring

Groundwater monitoring was considered a priority on the project as a previous cut and cover project on the northern fringe of Perth CBD had suffered numerous claims for damages from surrounding residents as a result of dewatering activities. It was also acknowledged that dewatering and subsequent depressurisation of the underlying confined aquifers would be required to facilitate construction, and that this dewatering would be accompanied by recharge. As the groundwater level was within 2-3 metres of the surface through the whole project it was acknowledged that all excavations would require some sort of dewatering measures and detailed monitoring.

Approximately 20 monitoring bores were installed by others during the site investigation phase and these formed the basis of the monitoring program. Typically open hole standpipes (OHPZ’s) had been installed in the upper unconfined aquifer which was typically Spearwood Sands or sand fill. Nested OHPZ’s and nested vibrating wire piezometers (VWPZ’s) were also installed. Occasionally individual holes had been drilled for deeper VWPZ’s. The nested piezometers proved highly unreliable due to their construction methods. It was found that many nested piezometers from the initial SI stages were leaking, resulting in water levels from the upper perched aquifers corrupting the lower confined aquifer readings. These initial results led the designers to incorrectly believe there was a “wetting front” occurring during winter. This leakage was proved by later installations during the construction phase, which clearly defined the perched water table. One piezometer, which was on the perimeter of the jet grouting area at Horseshoe Bridge highlighted the leakage as the jet grouting rectified the leaky zone and resulted in a sharp drop in water pressure as illustrated in Figure 41. The drop in water pressure corresponded with the initial water pressure measurement 2 ½ years earlier, and also corresponded with similar instruments located at depth in that area. The false increase in water pressure caused by leakage after installation can also be seen in Figure 41. Detailed analysis of the

inherited bores that leaked, showed that a minimum of 5 metres of grout was required for an effective seal in a nested piezometer for it to work properly. This rule of thumb was adopted for all nested piezometers that were installed during the project.

Piezometric Pressure at BH 0004

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Ch 81.313 PB Up

Figure 41 – Example of Leaky Piezometer due to insufficient bentonite seal

A further 217 piezometers were installed on the project in the initial two years. Initially the piezometers were drilled using rotary methods, with OHPZ’s being installed in the unconfined upper aquifer, and VWPZ’s being installed in the lower confined aquifers. The initial VWPZ’s were installed in nested holes with gravel packing around the piezometer and cement-bentonite grout in between. Whilst this method of installation was effective, it was time consuming and costly in terms of installation, and also did not allow for verification of readings, or removal of VWPZ’s for re-use elsewhere.

To improve cost effectiveness and productivity, two improvements to the method of installation were instigated by the author. Firstly, instead of grouting VWPZ’s in the hole, 20mm PVC (electrical conduit) was installed in a hole to the desired depth, with the bottom response zone slotted over the desired interval. A 50% bentonite 50% gravel mix was then placed within filter sock and tied just above the slotted zone, and then pushed down through the drill pipe with the PVC pipe as shown in Figure 42. As the filter sock passed out through the base of the drill pipe it formed a self sealing plug against the hole wall. The zone of interest was then sealed without the need for gravel pack, ensuring the grout above does not contaminate the response zone. Grouting of the zone above the piezometer of the remainder of the hole was then undertaken in the normal tremied fashion.

Using this method of installation, the initial water pressures were then measured with a manual dip meter, which fits down the inside of the PVC pipe. The hole was also then bailed with ball valve bailer to check for signs of grout or sediment. After a period of a few days, water pressures were rechecked and a VWPZ was installed within the PVC pipe to the desired depth. The cable is then silicon sealed at the top of the PVC pipe to create a pressure seal within the monitored interval.

initial g/w pressure

hole filled by surface runoff

jet grouting

perched aquifer level

true g/w pressure

Leakage from perchedaquifer

Response Zone

Silicon Sealant (used to form pressure seal)

Soil 1

Cement & Bentonite Seal

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VWPZ inside Slotted PVC (20mm)

Figure 42 - Piezometer Installation with Self Sealing Plug

If the aquifer was confined, the sealing would result in an increase in water pressure as the effect of external air pressure on the water table would no longer occur. This effect was observed many times on the project in the confined aquifers. The instruments installed in unconfined aquifers showed no rise in pressure, which was expected. This effect is illustrated in Figure 43 where the shallow unconfined/leaky aquifers showed no increase in pressure, whilst the deeper confined aquifer showed a pressure increase in response to sealing of the monitored interval. To remove the VWPZ’s at the end of the project, the silicon was simply cut away and the VWPZ removed for re-use. The hole also remained in place for continued manual monitoring.

Piezometric Pressure at BH 2193

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OHPZ_BH2193AOHPZ_BH2193A Response Zones Ground LevelOHPZ_BH2193BOHPZ_BH2193B Response ZonesOHPZ_BH2193COHPZ_BH2193C Response ZonesVWPZ_BH2193AVWPZ_BH2193A Response ZonesVWPZ_BH2193BVWPZ_BH2193B Response ZonesVWPZ_BH2193CVWPZ_BH2193C Response Zones

Ch 702.621 PM Dn

No Pressure rise due to sealing of VWPZ in unconfined aquifer

Pressure rise due to sealing of VWPZ inunconfined aquifer

Basal Gravelly Sand

SRA

Fill

Figure 43 - Piezometer Response to Sealing of Monitored Zone

A second innovation that was adopted for installation of piezometers was the use of the small Geo-Probe 6610DT direct push drill which was operated by Ecoprobe in Perth (Figure 44). The Geo-Probe utilises static force and hydraulically powered percussion to advance sampling tools into the soil. This very small rig was able to obtain continuous soil cores to depths of at least 20m and install piezometers in these holes in minimal time, and at less than half the cost of comparable rotary techniques. Due to the rapid drilling ability of the Geoprobe rig, nested piezometers were abandoned

and instead individual holes were drilled for each piezometer, thus ensuring the zone of interest was being monitored. A initial deep hole was cored continuously from the surface, allowing perfect selection of the optimal location for piezometer installation near the base of the hole using the piezometer installation method described previously in this section. The continuous core was then used to select further intervals for installation of piezometers in adjacent holes. In the adjacent shallower holes, the probe was then blind pushed to the nominated depth without coring as a metre of drilling could be achieve in 1-2 minutes using this method. Once the desired depth was reached, the probe was pulled back and a sacrificial shoe bit released allowing installation of a piezometer through the drill pipe at the desired interval. This method ensures that no drilling chemicals or fluids contaminate the monitored zone, and that the interval is completely sealed outside the zone of interest ensuring the integrity of the results, which is much preferred to standard nested piezometers.

Figure 44 a and 44b – Geo-Probe 6610DT Rig

The rig was found to be very cost effective due to its ability to drill holes rapidly, with a metre of sands or soft clays typically drilled within 2-3 minutes. As this is a single tube system this rate diminishes with hole depth, however it is still more productive than rotary techniques. On the project, several piezometer locations containing 3 piezometers each, were drilled, installed and grouted each day. This level of productivity was 2-3 times more productive than a comparable rotary rig, whilst also producing a higher quality monitoring installation. Being a single man operation, the drilling running costs were also less than half of that for a normal 2-3 man rotary rig. Thus the overall savings on installation were substantial, whilst producing a higher quality result. The rig was also used for environmental sampling of acid sulphate soils and groundwater on the project with 10-15 holes per day drilled to a depth of 10-15 meters.

Groundwater levels and pressures on the project were measured using traditional electric dip meters and VWPZ’s. Both instruments were supplied by SINCO. Manual dipping of OHPZ’s was typically undertaken weekly and as such daily changes in response to dewatering activities generally could not be determined. The durability of the dip meters was typically poor, as is the case with most brands of electric dip meter, with wear and tear on the thin plastic tape which contains the conductive wires common, due to it running over the borehole collar. Typically this tape was repaired in house by hot fixing a plastic sheath over the effected area.

VWPZ’s were logged every 15 minutes with data being stored in SINCO miniloggers and downloaded every 7-14 days. The quality of the data obtained using the VWPZ’s was excellent, with responses to dewatering immediately visible and responses to pump tests clearly noticeable within minutes, at points up to 500 metres from the pump test. The VWPZ’s proved to be completely reliable throughout the project with no recorded instrument failures during the project, however the miniloggers proved to be less than desirable with more than 75% lost due to internal corrosion caused by condensation or leakage of the water tight seal on the lid as illustrated in Figure 45. The miniloggers were susceptible to leakage and corrosion when placed in boreholes under manhole covers, however when they were simply left on the ground or on struts, and exposed to rain they performed excellently.

Figure 45 – Corroded Miniloggers due to Condensation

Figure 46 – Illustration of Potential Back and/or Personal Injury due to Repetitive Bending over a

Borehole

Whilst the quality of VWPZ data was high, weekly or fortnightly downloading of data did not allow for the dewatering/recharge system to be adequately controlled. This was considered a significant detriment to the project, as the piezometers were not being used for their intended purpose of controlling the dewatering/recharge system. The use of automated monitoring with live data feed should therefore be considered a basic requirement for similar types of projects. The labour cost to measure OHPZ’s and download VWPZ’s on this project was in the order of A$250,000, with a monitoring technician being employed full time for approximately 2 years, and the cost of replacement miniloggers was in the order of A$50,000. A totally automated system could have been installed for less than A$100,000 and would have resulted in substantial cost savings in monitoring and dewatering running costs. In addition to the above, a fully automated system, buried a metre or so below ground would have negated the need for continuous vigilance and ongoing negotiation with construction personnel that was required to prevent damage to the boreholes and instruments, thus saving valuable management time and frustration.

With an automated system, the danger to monitoring personnel would have been dramatically reduced as potential injuries from carrying equipment ,and bending over holes as illustrated in Figure 46 would have been eliminated, and high potential injuries, such as being hit by large equipment or cars (as the worker cannot be seen bending over the hole) would have been negated.

5 MONITORING RESULTS/EXPERIENCE

The quantity of data obtained on the project was enormous, with several million individual readings obtained each week.. To present one particular example of how it was applied on a daily fashion to verify the ground response to construction would be an injustice, so several examples of the outputs from key construction activities are discussed in the following paragraphs.

5.1 Settlement and Lateral Movement of Sheet Piled Excavations

Settlement monitoring around the sheet piled excavations was a key activity on the project. Monitoring of the deep excavations at the tunnel launch box and the tunnel receival box highlighted many key issues.

The experience at both these locations, and at the rest of the sheet piled excavations was that wall movements and initial settlements were much greater than expectations, especially where soft alluvium existed. Wall deflections of >100mm occurred in response to the initial shallow excavation of 1-2 metres at the launch box between 18/10/04 -21/10/04 as shown in Figure 47 a to c. The recorded movements in response to this initial excavation are illustrated in the retro target summary in Figure 48, and the inclinometer plot in Figure 50. The wall movements resulted in large tension

cracks as shown in Figure 47b. These tension cracks were visible adjacent all sheet piled excavations throughout the project after initial excavation. In this launch box example, the cracks filled with water after heavy rain and further exacerbated wall deflection by increasing the force on the wall.

This example indicates that significant ground movements can occur adjacent sheet piled excavations in cantilever, even when thick (20-32mm) sheet piles are used. Finite element modelling of this and other sheet piled excavations was undertaken using PLAXIS, with only 10mm of wall deflection predicted during this first stage Launch Box excavation, thus PLAXIS was found wanting in its predictions of wall deflections in this cantilever stage.

Settlements of up to 35mm were recorded at a distance of 5m behind the sheet piles in response to this first stage of excavation as illustrated in Figure 49 and Figure 51 , with settlements of >100mm likely adjacent to the sheet piles. The vertical settlement in comparison to 1st Stage design was more than double design expectations.

Subsequent settlement monitoring of the Launch Box and the Receival Box excavation showed that settlements were typically equal to or greater than design expectations, but at distances < 0.5D away from the excavation, settlements were substantially greater than expectations as shown in Figure 52.

Figure 47 a – Initial Excavation in Box Launch

Figure 47 b – Cracking and Lateral Movement in Response to

Excavation

Figure 47 c – Lateral Sheet Pile Movement in Response to

Excavation

Esplanade Launch Box Sheet Pile Movements - Excavating to -0.5 mRL, 21/10/04

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Figure 48 – Lateral Sheet Pile Movements in mm in Response to Initial Launch Box Excavation as shown in Figure 47 a

Figure 49 – Settlement Response to Initial Launch Box Excavation Shown in Figure 47 a

Figure 50 – Inclinometer Response to Initial Launch Box Excavation (1m from Sheet Pile)

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Launch Box Excavation - Stage 1 Excavation to -0.5mRL (2.5m depth) Settlement v Design (Plaxis Model ESLS_4d)

Large Settlement in North and North West due to large deflection of north wall and service diversion

Figure 51 – Cross Sectional Settlement Plot of Initial Launch Box Excavation as Shown in Figure 47 a

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Launch Box Excavation - End of Base Slab Construction Settlement v Design (Plaxis Model ESLS_4d)

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Figure 52 – Cross Sectional Settlement Plot after Excavation of Final Launch Box Level

Detailed examination of the excavation data would indicate that the ground response curve for this and other sheet piled excavations on the project could be developed and fitted to the data as illustrated in Figure 53. However additional settlement occurred in close proximity to the excavation due to the loading and passing of tracked cranes, trucks and excavators which is clearly visible when the data is contoured as illustrated in Figure 54 and Figure 55. Despite these loadings being simulated by a 20 kPa uniform loading in PLAXIS, the effect of consolidation of the upper layer by multiple passes was not accounted for by the software, or any other empirical correlation. Experience on the project showed that an allowance of 30-50 mm of settlement should be allowed for in settlement predictions where construction traffic occurs. This experience was best illustrated at the receival box where a point in the SE corner of the receival box was directly under a crane for extended periods and showed approximately 40mm of settlement which was due only to the presence of the crane. The blue and white crane can be seen in the top centre of Figure 13 and the resultant settlement visible in the bottom right of Figure 55. Similar differences in peak settlement were observed adjacent sheet piles where

heavy construction traffic was placed. Hence the following empirical relationship for measured settlement was developed for the project.

For 0- 0.5D from the sheet piled excavation:

Settlement = Design Movement + 0.2* Maximum Design Settlement + 40mm

For 0.5 to 2D from the sheet piled excavation:

Settlement = Design Movement + 0.2* Maximum Design Settlement

For 2D TO 3D from the sheet piled excavation:

Settlement = Straight Line Integration of Experience Curve and Design Curve

The relationship is illustrated in Figure 53 along with other empirical correlations commonly used as reference curves. The other reference curves proved not to be applicable.

• Whilst the developed empirical relationship is not directly applicable to all other projects, the basic findings of the empirical relationship should be applied to the design and monitoring of other projects in soft clays and/or sandy soils as follows:

• Approximately 40-50mm should be added to all numerical modelling designs in areas of construction traffic, to allow for consolidation effects.

• The assumed maximum allowable settlement / ground movement should not simply be 120% of the design value, but rather design risk assessments and monitoring should allow for 20% of the maximum predicted settlement to be added to the design value to be considered as the maximum allowable settlement

• Lateral movements from cantilever supported excavations in the order of 50-100mm are likely in soft soils and should be considered.

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Plaxis Drained - End of Excavation Actual Settlement Previous Stage BOWLES Semi-empiricalBOWLES-3*D Design + 20% Max Design Experience Curve

Launch Box Excavation - End of Base Slab Construction Settlement v Design (Plaxis Model ESLS_4d)

Design + 20% Design Max

1D 2D 3D

Design + 20% Design Max + 40mm

Figure 53 – Contoured Plot of Settlements at Receival Box at End of Excavation

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Date Printed: Authorised for Distribution:

Settlement

Heave

Data is total change from 15/10/04 to 28/2/05

Stage 4 Excavation Complete 18/1/05 (CH 535 - CH 571)Final Excavation Commenced 23/1/05 (CH 535 - CH 571)Final Excavation Complete 28/2/05 (CH 535 - CH 571)

Launch Box Excavation Induced Ground SettlementFrom Start of Excavation to End of Final Excavation

Figure 54 – Contoured Settlement Plot After Excavation of Final Launch Box Level

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Heave (mm)

Settlement (mm)

Perth Yard Settlement from Tuesday, 30 November 2004 To Wednesday, 22 November 2006

Plot created: Monday, 29 January 2007 11:01Plot by: Kent Wheeler

Authorised for issue:

Site Information:Contours Created from Data AvailableSince Sheetpile Removal till 22/11/06

Figure 55 – Contoured Plot of Settlements at Receival Box at End of Excavation

Crane and Excavator Locations

Crane and Excavator Locations

5.2 Ground Movement due to Bored Tunnelling

The quantity and degree of settlement monitoring applied to the EPB tunnelling process proved to be a great contributor the success of the tunnel drives under Perth with minimal ground movements being achieved. The intensity and frequency of monitoring when combined with various means of presentation allowed the tunnel team to continuously refine their operation and maintain volume losses well below design and in line with world’s best practice.

The SWTC called for a minimum of centreline monitoring every 25m with heavily instrumented cross sectional profiles every 200m. These minimum quantities were found to be insufficient for the purpose of tunnelling, and a much higher density of monitoring was applied to project. Typically, a minimum of 5 monitoring points were installed every 12.5 metres along the tunnel alignment to ensure that new excavations during each shift could be monitored. In addition to this, the adjacent buildings were monitored with a minimum of 4 settlement points, as were the adjacent footpaths and kerbs.

The density of monitoring, and spread of monitoring, allowed consistent cross-sectioning, contouring and long sectioning to be developed. This output would not have been possible with lesser quantities of monitoring. Long sectional profiles like Figure 56 were provided each shift and clearly illustrate the heave due to face pressure, and the development of the settlement trough with time and distance. Cross sectional profiles illustrating the movement of the past 4 days were also provided each shift.

Detailed cross sectional summaries were also done by the author after each tunnel run, (Figure 57 and Figure 58) illustrating the initial heave, settlement, and volume loss per 20m section, with these used by the tunnel team to optimise the next tunnel run. Final summaries of the combined tunnel movement were also produced at the end of tunnelling as illustrated in Figure 59 and Figure 60 These summaries highlight the fact that the maximum recorded ground movements typically were not equal to the final ground movement due to tail void grouting effects and reducing heave as face pressure diminishes. Contoured summaries of the maximum heave, settlement and final ground movement with respect to each run and with respect to the initial tunnel baseline were also developed. A typical contour plot showing the total ground movements from the tunnel baseline is shown in Figure 61.

Figure 56 – Long Sectional Plot of Ground Movement With Time and Distance

Maximum Ground Movement Profile Due to Bored Tunnel North 2 Excavation- CH 207 PBdn (CH 220 PBup)(Chainage: 207 PBdn +/- 10m Tunnel 2)

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27/09/2006 6:001/10/2006 6:005/10/2006 6:009/10/2006 6:00Design Volume Loss CurveActual Volume Loss

K=0.45, Vloss = -0.33% ActualVloss = -0.56% If Straight

Tunnel 2 Cutter Face at CH 197 PBdn approx 02/10/06 06:00Tunnel 2 Cutter Face at CH 217 PBdn approx 03/10/06 06:00

K=0.4, zo = 9.5mDesign Vloss = 0.83% CurvedDesign Vloss = 0.60% If StraightDesign Curve Radius = 135mDepth of Cover 6.0m

Maximum Ground Movement Profile Due to Bored Tunnel North 2 Excavation- CH 207 PBdn (CH 220 PBup)(Chainage: 207 PBdn +/- 10m Tunnel 2)

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27/09/2006 6:001/10/2006 6:005/10/2006 6:009/10/2006 6:00Design Volume Loss CurveActual Volume Loss

K=0.45, Vloss = 0.03% ActualVloss = 0.00% If Straight

Tunnel 2 Cutter Face at CH 197 PBdn approx 02/10/06 06:00Tunnel 2 Cutter Face at CH 217 PBdn approx 03/10/06 06:00

K=0.4, zo = 9.5mDesign Vloss = 0.83% CurvedDesign Vloss = 0.60% If StraightDesign Curve Radius = 135mDepth of Cover 6.0m

Figure 57 – Cross Sectional Plot of Ground Heave with Time for Single Tunnel Run

Figure 58 – Cross Sectional Plot of Ground Loss with Time for Single Tunnel Run

Maximum Ground Movement Profile Due to Bored Tunnel North 1 and 2 - CH 207 PBdn (CH 220 PBup)

(Chainage: 207 PBdn +/- 10m Tunnel 2)

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26/09/2006 6:0030/09/2006 6:004/10/2006 6:008/10/2006 6:00Design Volume Loss CurvePredicted Volume LossMeasured Volume Loss

Predicted volume loss curve from BTN 1 and BTN 2 Individual ProfilesBTN 1 K=0.45, Vloss = 0.30% ActualBTN 2 K=0.45, Vloss = 0.03% ActualPredicted Vloss = 0.33%

Tunnel 2 Cutter Face at CH 197 PBdn approx 2/10/06 06:00Tunnel 2 Cutter Face at CH 217 PBdn approx 3/10/06 06:00

Design Vloss CurveK=0.4, zo = 9.5mDepth of Cover 6.0m

Measured volume loss profile from BTN 1 baselineBTN 1 K=0.42, Vloss = 0.26% ActualBTN 2 K=0.45, Vloss = 0.03% ActualTotal Vloss = 0.29% Actual

Figure 59 – Interpreted Ground Movement Immediately After Tunnel Completion

Maximum Ground Movement Profile Due to Bored Tunnel North 1 and 2 - CH 207 PBdn (CH 220 PBup)(Chainage: 207 PBdn +/- 10m Tunnel 2)

Tunn

el 1

Cen

trelin

e

Tunn

el 2

Cen

trelin

e

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

-50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0

Offset from Project Centreline (m)

Gro

und

Mov

emen

t (m

m)

12/10/2006 6:0019/10/2006 6:0026/10/2006 6:002/11/2006 6:00Design Volume Loss CurvePredicted Volume LossMeasured Volume Loss

Predicted volume loss curve from BTN 1 and BTN 2 Individual ProfilesBTN 1 K=0.45, Vloss = 0.30% ActualBTN 2 K=0.45, Vloss = 0.03% Actual

Tunnel 2 Cutter Face at CH 197 PBdn approx 2/10/06 06:00Tunnel 2 Cutter Face at CH 217 PBdn approx 3/10/06 06:00

Design Vloss CurveK=0.4, zo = 9.5mDepth of Cover 6.0m

Measured volume loss profile from BTN 1 baselineBTN 1 K=0.35, Vloss = 0.18% ActualBTN 2 K=0.45, Vloss = -0.04% Actual

Figure 60 – Interpreted Ground Movement 2-4 Weeks After Tunnel Completion

-1.9

1.4

-2.8

1.6

-0.9 -0.5

-0.1 0.9 -0.8 -0.5-0.8

-0.7

-1.6

-2.9 -3.6 -2.5 -1.8 -1.3-2.0

-3.0-1.9

-0.8 -2.8

-3.1

-2.4 -1.4

-1.6

-0.8

2.33.21.92.0-0.20.4

2.01.9

0.61.1

2.3 4.6 1.9 0.6 0.10.8 1.0

0.3

-1.2

-0.7

-0.9

-3.3

-0.9

0.7

0.6

0.5

1.5

4.7 2.5 0.5 2.0

-2.1

0.7

4.12.3 0.0

0.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1.3

1.4

-1.6-1.9

-4.3

-1.0

-1.7

-1.6

0.7 0.20.3

-0.10.4 -0.0 -0.1 -2.1

-1.7-1.8 -1.7 -1.0 0.0 0.4 0.6 0.7

0.30.6

-0.1

0.4 0.80.9

-0.4

0.9

-0.1

-0.3

0.6

0.6

0.0

0.7

-0.2

0.4

3.6

2.7

7.6

5.0

1.0

-0.3

-0.1

0.3

4.5

-1.2

-2.4

2.1

-1.0

0.3

0.0

-0.3

0.4

-3.2-3.8

-1.1

-1.3-0.9

-1.9-3.8

-3.9-3.1

-3.5-3.7

2.2

-1.8

3.21.7

1.7

-9.7-5.9

-1.1

4.1

-0.3-5.5

-0.5

1.6

-0.2

-2.7

-7.2-0.4

0.5

-0.7

0.3

-0.4

0.0

-5.1

-0.8-0.5

-0.2

0.5

-0.7

-3.0

1.5

5.2

-7.3-7.2

4.0

-4.6

-1.7

-1.6-4.7

-3.6-4.7

1.4

3.3

-10.6

-4.5

-3.3

-4.4

0.81.2

8.8

0.9

4.1

-4.7-6.4

-7.6-8.3

-3.4

-0.1

-5.0

-8.4

-0.1

0.1

-4.5

-0.4

-6.9

-5.4

-1.9

-1.2

-3.8

-2.2

-1.5

0.3

-1.1-2.1

-0.6

-0.3

-0.7

-1.5

-0.6-3.4

-2.0

0.5

0.9

-3.4

1.6

-0.8

0.1

4.05.2

-0.8-1.1

-0.21.0

0.40.2

-0.11.3

-0.72.4

-1.6-0.4

-1.6-0.5

-0.8-2.3

-2.1-1.4

-3.5-2.7

-2.2-2.1

0.6-0.4

-0.71.4

-1.9-1.2

-1.9-2.1

-0.4-0.9

1.0-0.2

-0.3-0.7

-0.81.2

0.4

-0.01.0

2.5

-2.1-0.1

1.3

0.12.0

-0.1-0.5

-1.0

-1.4-0.9

-1.5-1.3

-2.2-2.1

-4.7-5.3

-5.6-5.6

-4.3-3.7

-2.9-3.4

-1.0-2.4

-4.9-6.6

-5.5-5.6

-0.5-4.0

-2.3-3.2

-0.9-1.4

-1.2-0.2

-0.1-0.2

-0.3-0.7

-0.4-0.3

1.10.3

-0.5-0.9

0.9

0.30.7

-0.61.00.11.2-0.20.8-0.10.30.2-0.4-0.30.8-1.8-0.6-0.2-1.1-0.81.01.3-0.10.0-5.8-5.1-7.8-8.2-5.7-6.90.6-0.71.60.20.70.90.5-1.2-1.5-3.5-1.7-1.5-2.2-1.0-3.3-2.7

-2.4-2.5-1.5

-2.1

-0.6-0.6

-5.1-4.7

-9.4-7.4

-7.2-7.8

-3.1-2.8

-3.6-3.9

-4.8-4.3

-5.2-5.1

-2.5-3.2

0.3-0.3

0.1-0.1

-2.5-3.2

-1.7-2.7

-0.0-0.9

-5.3-7.9

-8.3-7.8 -5.0

-6.1

0.3-1.8

-0.4

-7.5

-5.6

-7.1

-3.7-3.1

-0.5

-0.6

-0.2-1.0-1.1

-0.4

0.3

-1.4

-2.0

-2.7-3.6

-4.9

1.1

1.2

-2.8-1.8

-1.7-2.4

-8.2

-10.2

-9.9

-9.7

-11.0

-10.0

-6.5

-2.2

-9.2

-4.6

-1.3

-0.1

-7.4

-1.1

-0.4

-0.2

-0.3

-1.5

-2.1

-2.9

-2.7-1.0

-1.6

-4.2

-4.9

-2.7

-1.3

0.2

-0.2

-0.5

-0.5

-1.2

-2.0

-4.6

-6.2

-5.6

-3.7

-5.4

-11.5

-10.5

-4.1

-0.9

-0.6

-0.0

-0.2

-1.9

0.6

-2.3-3.7

-2.8

-0.6

-2.1

-9.0

-9.2

-5.8

-0.0

0.6

0.6

0.2

1.4

1.4

SSP_0573

SSP_0582

SSP_0587

SSP_0596

SSP_0602

SSP_0605

SSP_0611 SSP_0612 SSP_0613SSP_0614

SSP_0615

SSP_0621

SSP_0626

SSP_0642SSP_0643 SSP_0644SSP_0645

SSP_0646SSP_1029

SSP_1032SSP_1033

SSP_1034SSP_1035

SSP_1037

SSP_1039SSP_1040

SSP_1042

SSP_1044

SSP_1048SSP_1049

SSP_1050SSP_1051

SSP_1052

SSP_1053

SSP_1054

SSP_1055

SSP_1250 SSP_1251

SSP_1252

SSP_1253 SSP_1254

SSP_1255SSP_1256

SSP_1257SSP_1258

SSP_1260

SSP_1261

SSP_1262

SSP_1263

SSP_1264

SSP_1265

SSP_1266

SSP_1267

SSP_1340SSP_1352

SSP_1355SSP_1357

SSP_1359SSP_1361

SSP_1393

SSP_1394

BH2148

BH2149BH2151

SCP006

.

.

.

.

.

.

.

.

.

BSP_001_029BSP_001_030

BSP_001_034

BSP_001_035

BSP_001_036

BSP_001_041

BSP_001_042

BSP_001_043

BSP_003_012

BSP_003_013BSP_003_014BSP_003_015BSP_003_016BSP_003_017

BSP_003_018BSP_003_019

BSP_003_020BSP_003_021BSP_003_022

BSP_003_023BSP_003_024

BSP_003_025

BSP_003_026

BSP_003_027

BSP_003_028

BSP_003_029

BSP_003_030

BSP_003_031

BSP_003_032

BSP_003_033

RT004

RT090

RT091

RT092

RT093

RT094

RT102

RT103

RT111

RT112

SSP_0717A

SSP_0725A

SSP_0729A

SSP_0737

SSP_0737A

SSP_0738

SSP_0741A

SSP_0742A

SSP_0743A

SSP_0744

SSP_0745

SSP_0747

SSP_0748

SSP_0749

SSP_0751SSP_0752

SSP_0753

SSP_0758ASSP_0758B

SSP_0850

SSP_0851SSP_0853

SSP_0857

SSP_0859SSP_0863SSP_0865

SSP_0871SSP_0873

SSP_0874B

SSP_0875

SSP_0923BSSP_0923D

SSP_0924

SSP_0925ASSP_0925B

SSP_0926A

SSP_0927

SSP_1268SSP_1268A

SSP_1270

SSP_1276SSP_1277

SSP_1278SSP_1279 SSP_1280

SSP_1281

SSP_1283

SSP_1284

SSP_1285SSP_1286

SSP_1287

SSP_1288SSP_1289

SSP_1291

SSP_1292

SSP_1292ASSP_1293

SSP_1294

SSP_1294B

SSP_1295SSP_1295A

SSP_1297

SSP_1298

SSP_1298A

SSP_1298BSSP_1298CSSP_1299SSP_1299A

SSP_1300

SSP_1301

SSP_1302

SSP_1303

SSP_1304

SSP_1305

SSP_1306SSP_1307

SSP_1308

SSP_1309

SSP_1311

SSP_1313SSP_1313A

SSP_1314SSP_1314A

SSP_1315

SSP_1317

SSP_1318

SSP_1319

SSP_1320

SSP_1323

SSP_1324

SSP_1325

SSP_1326

SSP_1327

SSP_1328

SSP_1329

SSP_1330

SSP_1331

SSP_1332

SSP_1513

SSP_1517SSP_1518

SSP_1519

SSP_1520

SSP_1530

SSP_1531

SSP_1532SSP_1533

SSP_1534

BSP_053_001

BSP_053_002

BSP_053_003

BSP_053_005

BH2168Bolt

EB401

EB402

EB403

EB404

EB405

EB406

EB407

EB408

EB409

EB410

EB411

EB412

EB413

EB414

EB415EB416

EB417EB418

EB419

EB420

EB421

EB422

EB423

EB424

EB425

EB426

EB427

EB428EB429

EB430

EB431

EB432

EB433EB434

EB435EB436

EB437

EB438

EB439

EB440EB442

EB443

EB444

EB445

EB446

EB448EB449

EB451

EB452EB453

EB454EB455

EB457

EB458EB459

EB460EB461

EB462EB463

EB464EB465

EB466EB467

EB468EB469

EB470EB471

EB472EB473

EB474EB475

EB476EB477

EB478EB479

EB480EB481

EB482EB483

EB484EB485

EB486EB487

EB488EB489

EB490EB491

EB492EB493

EB494EB495

EB496

EB498EB499

EB502EB503EB504EB505EB506EB507EB508EB509EB510EB511EB512EB513EB514EB516EB517EB518EB519EB520EB521EB522EB523EB524EB525EB526EB527EB528EB529EB530EB531EB532EB533EB534EB535EB536EB537EB538EB539EB540EB541EB542EB543EB544EB545EB547EB548EB549

EB551

EB602

EB603

EB604

EB605

EB606

EB607

EB608

EB609

EB610

EB611

EB612

EB613

EB614

EB615

EB616

EB617

EB618

EB619

EB624

EB625

EB626

EB627EB628

EB629EB630

EB631

EB632

EB633

EB634

EB635EB636

EB637EB638

EB639

EB640

EB641

BSP_001_002

BSP_001_006

BSP_001_007

BSP_001_008

BSP_001_009

BSP_001_010

BSP_001_011

BSP_001_013

BSP_001_016BSP_001_017

BSP_001_018

BSP_001_019

BSP_001_020

BSP_001_021

BSP_001_022

BSP_001_023

BSP_001_024

BSP_001_025

BSP_001_027

BSP_001_028

BSP_001_037BSP_001_038BSP_001_039BSP_001_040

BSP_001_044

BSP_001_045

BSP_001_046

BSP_001_047

BSP_001_048

BSP_001_049

BSP_001_050

BSP_001_051

BSP_001_052

BSP_001_053

BSP_001_054

BSP_001_071

BSP_001_077

BSP_001_101

BSP_001_102

BSP_001_103

BSP_001_104

BSP_001_105

BSP_001_106

BSP_001_107

BSP_001_108

BSP_001_109

BSP_001_110

BSP_001_111

BSP_001_112

BSP_001_113

BSP_001_115

BSP_001_116

BSP_001_117

BSP_001_118

BSP_001_119

BSP_001_201

BSP_001_202

BSP_001_203

BSP_001_204

BSP_001_205

BSP_001_206

BSP_001_207

BSP_001_208

BSP_001_209

BSP_001_210

BSP_001_211

BSP_001_212

BSP_001_214

BSP_001_215

BSP_001_216

BSP_001_217

BSP_001_301

BSP_001_302

BSP_001_303

BSP_001_304

BSP_001_305

BSP_001_306

BSP_001_307

BSP_001_308

BSP_001_309

BSP_001_310

BSP_001_311

BSP_001_312

BSP_001_313

BSP_001_314

RT004

RT008

RT011

RT012

RT025

RT027

RT030

RT033

RT090

RT091

RT092

RT093

RT094

RT100

RT102

RT103

RT104

RT110

RT111

RT112

RT113

RT743

RT9021

53800 53825 53850 53875 53900 53925 53950 53975 54000263500

263520

263540

263560

263580

263600

263620

263640

263660

263680

263700

263720

263740

263760

48

47

4 6

4 5

44

43

4 2

51

52

5 3

54

55

56

57

67

6 6

65

6 4

63

62

61

60

7 0

71

7 2

7 3

74

7 5

76

41

4 0

3 9

49

50

59

5 8

6 8

69

10

0 9

08

07

0 6

15

16

17

18

1 9

2 9

28

27

26

25

24

34

35

36

37

38

11

1 2

23

22

21

20

30

3 1

32

33

0 5

04

03

02

01

13

1 4

WIL

LIAM

-15-14-13-12-11-10-9-8-7-6-5-4-3-2-1012345678910

Heave (mm)

Settlement (mm)

Bored Tunnel North Ground Movement from All Tunnelling Works(8/5/2006 - 30/6/2006 & 19/9/2006 - 22/11/2006)

Plot created: Thursday, 1 February 2007 14:58Plot by: Kent Wheeler

Authorised for issue:

Survey Information:Data Attributed to Tunnelling ContouredClose out Surveys Conducted on all Areas

Figure 61 – Contoured Plot of Final Ground Movements in Response to Tunnelling

The results of these sections were analysed in detail for the northern drives where the tunnels were driven under live railways, and where depth of cover was between 1.5D and 0.5D (where D = tunnel diameter). Some of results are presented in Table 3. The successful combination of monitoring and tunnel team feed back resulted in very small maximum volume losses of 0.06-0.34%, averaging 0.17% on the first tunnel run and volume losses in the range of -0.23% to 0.24%, averaging -0.02%, on the second tunnel run. These volume losses/gains are considered to be world best practice especially considering the limited tunnel cover.

Table 3 – Bored Tunnel North Volume Loss and Trough Width Parameter

Bored Tunnel 1 North Bored Tunnel 2 North

Chainage Cover

Depth (m) Cover xD

Final Ground

Movement (mm)

Final Volume

Loss k

Final Ground

Movement (mm)

Final Volume

Loss (%) k 80 8.95 1.29 -3.5 0.18 0.60 0.0 0.01 0.55 100 10.40 1.50 -2.0 0.06 0.65 4.0 -0.15 0.95 120 8.01 1.16 -3.0 0.06 0.15 4.0 -0.17 0.52 140 7.30 1.06 -7.5 0.17 0.25 -3.0 0.15 0.55 160 6.70 0.97 -11.0 0.31 0.40 -7.0 0.22 0.40 180 6.66 0.96 -10.0 0.34 0.45 -6.0 0.24 0.45 200 6.24 0.90 -7.0 0.18 0.35 2.0 -0.04 0.45 220 6.33 0.92 -12.0 0.31 0.35 -5.0 0.13 0.55 240 5.97 0.86 -6.0 0.15 0.40 5.0 -0.10 0.45 260 5.52 0.80 -3.0 0.06 0.22 -1.0 0.04 0.35 280 5.16 0.75 -7.5 0.18 0.33 7.0 -0.11 0.15 300 4.71 0.68 -5.0 0.10 0.30 5.0 -0.09 0.22 320 4.30 0.62 -10.0 0.21 0.30 7.5 -0.13 0.30 340 3.73 0.54 -5.0 0.12 0.35 9.0 -0.23 0.45

Average 0.17 0.36 -0.02 0.45 Median 0.18 0.35 -0.07 0.45

Experience on the project indicated that the trough width parameter ‘k’ is a function of the tunnel cover as illustrated in Figure 62, and also was a function of the building cover as shown by the larger K values where the tunnel passed under the Horseshoe Bridge at CH 80-100. This finding contradicts the findings by Burland (2001), who states that “the value of K for surface settlements is approximately constant for various depths of tunnel in the same ground”. The tunnelled material in the northern drive was consistent, being predominantly sand fill, overlying natural sand with some clayey sand lenses, with the geology also consistent between tunnels. The trough width parameter derived from temporary heave due to face pressure also showed a consistent change in K with tunnel cover despite the face heave remaining consistent at approximately 0.25% volume gain. The average K value also varied between tunnels with the K value on the first run being much lower than that of the second run. This is most likely a result of the increased face heave experienced on the second run. There was no distinct relationship observed between ground movements and tunnel cover.

Relationship between tunnel cover and K Value

0.000.100.200.300.400.500.600.700.800.901.00

0.000.501.001.502.00

Cover xD

K BTN 1

BTN 2

Figure 62 – Relationship Between Tunnel Cover and K Value for Northern Drives

5.3 Ground Movement due to Tube-a-Manchette (TAM) Installation and Jet Grouting Methodology

The impact of TAM drilling density on drilling induced settlements was also an issue highlighted by the detailed monitoring on the project. Significant settlements of ground and buildings occurred due to installation of TAM pipes in a radial fan pattern from central shaft as illustrated in Figure 63 and Figure 64. Due to the close proximity of the TAM pipes at the start of the fan, combined ground losses occurred that were much greater than was expected from tunnelling and as such corrective grouting was required even before tunnelling commenced. The contours of ground loss radiated outwards indicating that the density of drilling was a prime cause of the ground loss experienced and deserves further study. The results indicate that preventative measures may result in more damage and expense than a well controlled tunnel may create, and as such the planning and control of preventative measures must be carefully considered before implementation.

SSP 509A

SSP 510A

SSP 511A

SSP 512A

SSP 513SSP 513A

SSP 513B

SSP 51

SSP 513ESSP 513F

SSP 514

SSP 514

SSP 514B

SSP 515

SSP 51

SSP 515B

SSP 516

SSP 51

SSP 517

SSP 51

SSP 517B

SSP 518SSP 519

SSP 519B

SSP 524SSP 525

SSP 525A

SSP 526SSP 527

SSP 527A

SSP 528SSP 529

SSP 529A

SSP 530SSP 531

SSP 531A

SSP 531B

SSP 531C

SSP 531D

SSP 532

SSP 532A

BSP-018-103

BSP-018-104BSP-018-105

BSP-018-106

BSP-018-107

BSP-018-108

BSP-018-109

BSP-018-110

BSP-022-001

BSP-022-002

SSP 1100SSP 1100a SSP 1101A

SSP 1102

SSP 1102a

SSP 1103A

SSP 1104

SSP 1104aSSP 1105

SSP 1105a

SSP 1106SSP 1106a

SSP 1107

SSP 1107a

SSP 1108SSP 1108a

SSP 1109

SSP 1109a

SSP 1111SSP 1111a

SSP 1112a

SSP 1113

SSP 1113a

SSP 1114SSP 1115

SSP 1116SSP 1117

SSP 1118 SSP 1118A

SSP 1119

SSP 1120SSP 1120A

SSP 1121

SSP_1122

SSP_1123

SSP_1124

SSP_1125

SSP_1126SSP_1127

SSP_1128SSP_1129

SSP_1130

SSP_1131

SSP_1131A

SSP_1131B

SSP_1132

SSP_1133

SSP_1134

SSP_1135

SSP_1136

SSP_1137

SSP_1138

SSP_1139

SSP_1140

SSP_1141

SSP_1142

SSP_1143

SSP_1144

SSP_1145

SCP065

-0 1

0

0 1

1

1 1

0

-1 1

1

1

0

0

0

0

-1-2 -10 -10

-1

-4

-2 -11

-10

-4-2 -9

-8

-3-1 -7

-8

-0-1 -9-8

-4 -4

-1 -2

-1-2

-2

-1 -2-2

-10

-8

-6-6

-3 -2 -3 0 -2-1

-0

-0

0

0

1

1

1

1

-4-5

-3-3

-2-2

-1-2

-

-

-

------

-

-

-

----

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53900

QU

ICKS

ILV

ER

BU

ILD

ING

AUSTRALIAN

REFLECTIONS

HBF

KFC

HUNGRY JACKS

FRIENDLIES

CHEMIST BUILDING

2634

08.02

6 N

5386

7.578

E

2633

56.98

9 N

5384

7.727

E

2633

48.3

N

5387

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1 N

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Settlement

William Street TAM Grouting - Suface and Building Movement to 9/11/05Last Reading Minus TAM Baseline Reading

Figure 63 – Ground and Building Settlement Due to TAM Installation

Com

men

ce G

rout

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ft E

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ce T

AM

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M d

n

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Red

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14.5125BSP-017-012 Ch 115.4

SSP 1102 - Ch 115.1

Baseline Value

Figure 64 –Building & Ground Movement in Response to TAM Installation and Compensation Grouting

Ground Movement

Building Movement

Stringent monitoring of another preventative measure; jet grouting of the launch zone in the forecourt of the 100 year old Horseshoe Bridge (Built in 1903 and shown at that date below), was required to prevent damage to this historic structure.

Figure 65 - Horseshoe Bridge Circa 1903

The monitoring team quickly identified that movements outside of the allowable specification were being incurred as illustrated in Figure 66 and Figure 67. A rapid assessment indicated that the prime cause was that adjacent jet columns were being jetted too soon resulting in unacceptable ground movement. The adjacent jet grout columns are highlighted in grey on the top left of the jet grout block in Figure 66. The jet grout process is described in more detail in Sigl et.al. (2007a)

A change of sequencing was undertaken with a minimum period of two days between the jetting of adjacent columns implemented along with detailed monitoring continuing. The ongoing monitoring verified the course of action, as only one case of unacceptable ground movement occurred during the rest of the jet grout programme, with that being a result of departure from the agreed sequence. The success of the change in procedure implemented is illustrated in Figure 67, where the initial effect is clearly seen as a spike in heave and the subtle increase in heave seen over the remaining jet grouting columns except on the one occasion when protocol was not followed and a further spike in heave occurred.

Horseshoe Bridge - Absolute Suface Movement up to 15 SeptemberLast Reading minus Baseline Reading

Surface heave indicated by blue shading.Previous reading taken: 14 September 2004, amLast reading taken: 15 September 2004, amPlot generated: 27 September, 2004

Authorised for distribution:

-10 mm

-5 mm

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0 mm

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Heave

SettlementSSP551

SSP552

SSP553

SSP554

SSP555

SSP556

SSP557

SSP558

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SSP567

SSP568

SSP569

SSP570

SSP571

SSP572

SSP580

SSP581

SSP582

SSP583

SSP584SSP585

SSP586

SSP587SSP588

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SSP596

SSP597

SSP598

SSP601

SSP602

SSP603 SSP604

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SSP607SSP608

SSP610

SSP611

SSP612SSP613

SSP614SSP615

SSP616

SSP617SSP618

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SSP1004

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SSP1009SSP1010

SSP1011SSP1012

SSP1013

SSP1014 SSP1015

SSP1016

SSP1017SSP1018

SSP1019

SSP1020SSP1021SSP1022

SSP1023

SSP1024

SSP1025

SSP1026

SSP1027

SSP1028SSP1029

SSP1030

SSP1031

SSP1032

SSP1033

SSP1034SSP1035

SSP1036

SSP1037

SSP1038

SSP1039SSP1040

SSP1041

SSP1042

SSP1043

SSP1044

SSP1045

SSP1046

SSP1047

SSP1048SSP1049SSP1050SSP1051SSP1052

SSP1053

SSP1054

SSP1055

BSP-003-001 BSP-003-002

BSP-003-003

BSP-003-004

BSP-003-006

BSP-003-007BSP-003-008

BSP-003-009BSP-003-010

BSP-003-011

53925 53950 53975 54000 54025

Easting

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Surface settlement indicated by red shading.

Horseshoe Bridge deck contoured separately fromsurrounding ground.

Completed jet grout columns up to 14 September (am) highlighted by yellow circles.Columns completed in this period are grey.

Figure 66 – Ground Heave in Response to Jet Grouting Adjacent Recently Completed Piles

Horseshoe Bridge Settlement Points Movement v Time During Jet Grouting

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Figure 67 – Example of Ground Heave rising Rapidly in Response to Jet Grouting and Adjacent Recently Completed Piles

5.4 Structural Monitoring and its Geotechnical Implications

Structural monitoring provided a valuable tool in optimising excavations and construction sequences on the project as well as providing insightful feedback on the excavation and construction process, which can be adopted on other large excavations. Approximately 1100m of sheet piled excavations were undertaken on the project, with the majority of them strutted. There were between 1-4 levels of struts used in the excavations. Approximately 5% of these struts were installed with strain gauges to measure the loads within the struts. Four gauges per strut were used as a minimum.

The majority of sheet piled excavations were on the Foreshore and within the Perth Rail Yards. On the Foreshore the geology consists of reclaimed sand fill overlying very soft to soft alluvial sandy clayey silts and in the Perth Rail Yard the geology consists of shallow sand fill overlying medium dense sands with some clayey sand lenses.

The structural monitoring of the strutted excavations typically showed that increases in load with excavation were immediate and distinct as illustrated Figure 68 This immediate response was expected, and concurred with the inclinometer and settlement responses (Figure 69) which were typically measured a few hours to a few days later at the same location. This immediate response inferred a important engineering point that there appears to be no real stand up time with deep excavations in sands and soft clays, and the undrained condition is not apparent in deep excavations. The groundwater monitoring on the project also showed that the materials were highly permeable with rapid pore pressure changes in response to dewatering activities, and as such it is unlikely that there would have been increased pore pressure in response to excavation induced strain deformations, and therefore the undrained condition was unlikely despite the clayey nature of some of the materials encountered. The development of large tensile cracks during sheet pile installation, and during excavation would also lead to the conclusion that excess pore pressure is unlikely to develop as it would be dissipated rapidly through the tensile cracks.

Spike(s) in heave due to jetting of adjacent columns

less than 2 days apart

Strain Gauge - SG_FS_2027

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VWSG 210 Strut Load

VWSG 211 Strut Load

VWSG 212 Strut Load

Average Strut Load

SG_FS_2027 +Trigger

Average Temp

CH 696.664 PM Dn

Figure 68 - Typical Strut Load Response to Excavation and Strutting Activities

The strut loads, inclinometer and settlement data confirmed that sufficient strain occurs in within a few hours of excavation commencement to bring the excavation to the drained condition, and such even if the undrained condition is present effect is indiscernible and should be used only a check for stability in the design of deep retained excavations. A non-linear failure envelope should be applied to the modelling/design of large excavations as apparent strength is best determined by non-linear deformation/strain relationship in a drained excavation. In the rock engineering field, it is well recognised that a non-linear failure envelope exists for natural materials and that a drained model is applicable and no apparent undrained condition occurs in reality. The inapplicability of the undrained approach for predicting the ground response in retained excavations is highlighted in the settlement v design comparisons shown in Figure 53 where the drained estimates for the end of excavation stage shown were within 20% of measured values once an allowance for traffic consolidation is included. In contrast, the undrained model (which was not shown on Figure 53) predicted settlements that were <20% of the measured values and did not reflect reality.

Another simple but pertinent observation from the structural data is the effect of time on measured strut load is paramount as illustrated succinctly in Figure 68 and Figure 70. The monitoring of strut loads consistently showed that strut loads continued to increase unabated after each level of excavation had been completed, and only ceased increasing once a strut or base slab was in place. The time to complete install the next strut or slab was the key controller of strut load and as such only a few struts reached the design load. There was not sufficient exposure time in any of the excavations to confirm the assumption of a limiting load on a strut due to full activation of earth pressure forces, and as such the validity of the design load which was derived from PLAXIS modelling could not be verified. Whilst the design load was not exceeded, it was typically higher than that predicted by Peck’s empirical approach (Peck, 1969) by approximately 25%, and as such the typical forces measured on the struts within this project would have generally equalled or exceeded those predicted by empirical means.

Another key observation was that loads typically only increased once the adjacent strut was removed. There was typically no impact on strut loads when struts beyond the adjacent strut were removed.

This effect was repeated in the inclinometer observations, with effects from excavation and or strut removal more than 5 metres away generally not apparent.

Surface Settlement at - SSP_0124BC

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(T2)

1.685

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1.705

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1.725

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28-Sep-04

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22-Jul-06

Date

Red

uced

Lev

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AH

D)

SSP_0124B Reduced Level

Created: 01-May-07 21:32

Ch 701.235 PM Dn

Figure 69 – Rapid and Ongoing Settlement Response to Excavation

Strain Gauge - SG_FS_2059

1862

Laye

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trutti

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H 6

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CH

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Average Strut Load

SG_FS_2059 +Trigger

Average Temp

CH 696.664 PM Dn

Figure 70 – Example of Increase in Strut Load With Time During Excavation and After Excavation

5.5 Groundwater Monitoring and its Applicability to Perth

The groundwater monitoring on the project highlighted several groundwater related issues that are applicable locally to Perth CBD.

The first finding is that a perched water table exists throughout the Foreshore and up William Street. The Foreshore perched water table is a result of the reclaimed sand fill being placed on the Swan River Alluvium (SRA). The water table in the reclaimed fill is perched on top of the lower permeability SRA, which is expected given the contrast in permeability’s, and the assumed direct connection of the fill material with the adjacent Swan River. Despite this apparent direct connection there was no tidal effect observable in the reclaimed fill or the underlying SRA.

A similar perched effect occurs along William Street due to the consistent presence of a thin (0.5-1.0) organic silty sand, at the base of the Spearwood Sands in this area. The perched water table along William Street typically occurs at +8 to +10mRL and has no connection with the underlying groundwater water regime, which has maximum pressures equal to 0 to +2 mRL. This differential between the upper perched water table in William Street was illustrated in Figure 41 where the leakage between the two groundwater water tables was identified.

Below the perched water table on the Foreshore, there exists a further 3 to 4 separate aquifers. The underlying SRA is a leaky confined aquifer, which appears to be driven from the perched water table above. Groundwater pressures in the SRA match those in the fill above, however when pumping or spear dewatering occurred in the SRA as illustrated in Figure 71, the response in the SRA was independent of the fill above illustrating its confined nature. Also when pumping occurred in the fill materials there was no additional depressurisation response in the SRA below inferring that the link may not be direct.

In most areas of the Foreshore, the SRA directly overlies a thin gravelly sand layer, which overlies the basal Kings Park Formation. The basal gravelly sand layer was found to be consistent over the whole of the Kings Park Formation, spreading from the western end of the foreshore to the top end of William Street at Perth Station. This basal gravel and sand layer was found to be highly permeable, with immediate responses to pumping tests and dewatering effects seen up to 500 metres from the source. The pressure in the layer was found to be to consistent at 0 mRL on the Foreshore, and had continuous tidal fluctuations thus inferring the aquifer was confined and most likely connected to the river through the underlying King’s Park Formation.

Monitoring of the dewatering and recharge in this gravelly sand layer showed that whilst large fluctuations in pressure were occurring, there was no response in the upper SRA layer, with this effect also illustrated in Figure 71. The pressure in the layer along William Street was slightly higher than the Foreshore, showed more variation with seasons, and did not show any tidal response. A fourth aquifer existed on the Foreshore in the remnant paleochannel that cut through SRA. This clayey paleochannel, which physically is similar to the SRA but is uniquely different in age, is defined by its large oyster shell content. Surprisingly the pressures in this layer were slightly artesian and higher than the overlying SRA and underlying sandy gravel aquifer. There was no apparent hydraulic connection to the SRA or the underlying sandy gravel aquifer.

Below the Spearwood Sands along William Street the geology is predominantly sands and clayey sands with some 1-2m thick clay layers, which form part of what is currently described as the Guildford Formation. This aquifer is agglomeration of smaller leaky aquifers confined by the various clay layers and clayey sand lenses. The clayey lenses also contain fine gravel lenses, which exhibit high horizontal permeability’s. Thus the Guildford Formation acts as a series of leaky confined aquifers, which are not hydraulically connected to the overlying Spearwood Sands and also are not hydraulically connected to the underlying sandy gravel aquifer on top of the Kings Park Formation. Depressurisation within this intermediate aquifer only occurred when direct dewatering of the Guilford Formation occurred, however when dewatering was confined to the deeper sandy gravel aquifer there was no discernible pressure change in the overlying Guilford Formation aquifer.

Piezometric Pressure at BH 2094

Com

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7) C

omm

ence

d

Spea

r Dew

ater

ing

at U

nder

pass

Com

plet

ed

-20.00

-15.00

-10.00

-5.00

0.00

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10.00

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02-Mar-05

01-Apr-05

01-May-05

01-Jun-05

01-Jul-05

01-Aug-05

31-Aug-05

01-Oct-05

31-Oct-05

01-Dec-05

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30-Jan-06

02-Mar-06

01-Apr-06

02-May-06

01-Jun-06

Gro

und

Wat

er E

leva

tion

(mA

HD

)VWPZ_027A_BH2094VWPZ_027A_BH2094 TriggersVWPZ_027A_BH2094 Response Zones Ground LevelVWPZ_027B_BH2094VWPZ_027B_BH2094 TriggersVWPZ_027B_BH2094 Response ZonesVWPZ_027C_BH2094VWPZ_027C_BH2094 TriggersVWPZ_027C_BH2094 Response Zones

Ch 1219.624 PM Dn

Figure 71 –Differing Responses of Upper Unconfined & Lower Confined Aquifer at Foreshore

Piezometric Pressure at BH 0040

Pum

p Te

st in

ES

Lau

nch

Box

Com

men

ce D

ewat

erin

g in

ES

Lau

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ox

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ce D

ewat

erin

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spla

nade

Stn

Nth

Incr

ease

Dew

ater

ing

in E

S L

aunc

hbox

Incr

ease

Dew

ater

ing

Esp

lana

de S

tn

Com

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ce D

ewat

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g FS

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Incr

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Dew

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ing

FS A

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2

Red

uce

Dew

ater

ing

in E

S L

aunc

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Com

men

ce D

ewat

erin

g fo

r BTS

(T1)

Com

men

ce B

TS (T

1)

Com

men

ce D

ewat

erin

g fo

r BTS

(T1)

WS

S B

reak

thro

ugh

BTS

(T1)

WS

S B

reak

thro

ugh

Com

men

ce D

ewat

erin

g fo

r BTS

(T2)

Com

men

ce B

TS (T

2)C

omm

ence

Dew

ater

ing

for B

TN (T

2)

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

01-Mar-04

31-Mar-04

30-Apr-04

31-May-04

30-Jun-04

31-Jul-04

30-Aug-04

30-Sep-04

30-Oct-04

30-Nov-04

30-Dec-04

29-Jan-05

01-Mar-05

31-Mar-05

01-May-05

31-May-05

01-Jul-05

31-Jul-05

31-Aug-05

30-Sep-05

31-Oct-05

30-Nov-05

30-Dec-05

30-Jan-06

01-Mar-06

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01-May-06

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01-Jul-06

01-Aug-06

31-Aug-06

30-Sep-06

Gro

und

Wat

er E

leva

tion

(mA

HD

)

OHPZ_BH40S

OHPZ_BH40S Response Zones

Ground Level

VWPZ_BH40A

VWPZ_BH40A Response Zones

VWPZ_BH40B

VWPZ_BH40B Response Zones

Ch 84.709 PM Dn

Figure 72 - Differing Response of Middle Confined Aquifer & Lower Confined Aquifer at WSS

This relationship is illustrated in Figure 72 where pump testing of the basal aquifer in May 2004 showed a response only in the deeper aquifer. Subsequent dewatering of the basal sandy gravel aquifer on the foreshore produced a distinct depressurisation at William Street Station (WSS). Depressurisation of the intermediate Guildford formation also occurred at the same time as the underlying sandy gravel aquifer due to pumping at WSS and Perth Rail Yard, and could be mistakenly thought to be linked, however dewatering at the launch box for the first tunnel run in October 2005 clearly showed that the aquifers were independent with diverging trends apparent at this time. This was also apparent during the second tunnel launch in July 2005. This knowledge was not used when

Pressure drop in SRA. Rise in Fill due to recharge

Continued drop in basal aquifer due to

pumping. Rise in Fill and SRA due to cessation of spear

dewatering

No under drainage of SRA from depressurisation of basal aquifer

No connection between SRA or

fill with basal aquifer

Pumping only intermediate Guilford

Formation . No response elsewhere

Pumping only basal gravelly

sand aquifer, no response above

Pumping intermediate and basal aquifers

Basal aquifer response zone

SRA response zone

Fill Sand response zone

the TBM broke through into WSS for the 1st time in January 2006, with dewatering being undertaken in both aquifers at WSS with a resultant depressurisation of both aquifers. For the 2nd TBM breakthrough at WSS in August 2006 this information was used to benefit operations with dewatering being confined to the intermediate Guildford formation with resultant depressurisation being also confined to that aquifer thus further confirming its independence from the lower sandy gravel aquifer. With dewatering confined to this intermediate aquifer the dewatering quantities were substantially reduced in comparison to that extracted whilst trying to underdrain the intermediate aquifer. The pressure level in the Guildford Formation aquifer was typically between 0 to –2 mRL along William Street, and the pressure in the underlying sandy gravel aquifer between –2 to –3 mRL.

5.6 Vibration due to Tunnelling

Vibration due to tunnelling was expected to be noticeable during the project, due to the shallow cover, and the sandy nature of the soils under Perth. Monitoring highlighted that the geology and depth of cover had no influence on the ground vibrations emitted during tunnelling. Experience on the project also showed that vibration due to tunnelling was not consistent, and generally was a function of the turning radius of the tunnel, with no vibrations recorded when the tunnel was operating in a straight line, and vibrations recorded when the tunnel was turning. However, there were several occasions on the second tunnel run where very tight turning radiuses of 135 metres were being used and no vibrations were recorded, yet on some days the vibrations were distinct.

The background vibrations due to traffic above the tunnel were determined prior to tunnelling and post tunnelling, and were found to be consistent. A vibration sensor located in a borehole drilled through a traffic island at the bottom of William Street showed that background vibrations were consistent between the two tunnel runs as shown in Figure 73 and Figure 74. The peak background vibrations were consistent at approximately 1.0-1.1 mm/s in the Vertical Direction and 0.4-0.5 mm/s in the transverse direction. Long term monitoring showed that the traffic vibrations were consistently in the 9-13 Hz range in all directions. This is considered a good example of vibrations due to slow speed traffic and stopping, as this sensor was located in a traffic island at the base of a hill where distinct traffic vibrations occurred as a result of stopping at the lights at the base of the hill, and sharp turning at the base of the hill. The larger vertical vibrations are also consistent with expectations from traffic.

At the same location at the bottom of William Street (on the centreline of Tunnel 1), the vibrations of the TBM as it was being driven in a straight line toward the geophone during the two tunnel runs was indiscernible from the background vibration as shown in Figure 75 and Figure 76. The example from the second tunnel run shows that despite the recorded vibrations being less than normal background levels(0.8 mm/s vertical and 0.2mm/s laterally), there was still no discernible effect from the TBM. Field observations concurred with these measurements, as no vibration was discernible to the surveyors who were undertaking regular surveys above the TBM.

As the TBM progressed up William Street and commenced a slight turn, the vibrations could be clearly felt through the feet as you stood on the street above, and up to 20-30 metres from the TBM. The felt vibrations disappeared after this initial turn was complete and recommenced on the second turn at the Hay Street Junction. This phenomena was clearly visible in the optical sights of the surveyors’ levelling equipment.

In order to assess this phenomena and its effect on Buildings, a vibration sensor was installed in the Hungry Jacks Basement immediately above the first tunnel run. Background monitoring indicated that the vibrations in this building were very stable, and consistent with external phenomena as illustrated in Figure 77.

Figure 73 – Typical Background Ground Vibrations Due to Traffic Above Straight Tunnel Section Before Tunnel 1

Figure 74 - Typical Background Ground Vibrations due to Traffic Above Straight Tunnel Section Before Tunnel 2

Figure 75 – Measured Vibrations as Tunnel 1

Passed Under Monitoring Point at Base of William Street

Figure 76 – Measured Vibrations as Tunnel 2 Passed Under Monitoring Point at Base of William Street

In the basement, the background vibrations were less than 0.05 to 0.07 mm/s in the horizontal plane and 0.1 to 0.3 mm/s in the vertical plane due to traffic and vibrations from people in the restaurant above. They reduced during the night as is expected. This geophone highlighted the very subtle increase (<0.15mm/s) in horizontal plane vibrations as the TBM approached the monitoring point as shown in Figure 78 due to the TBM driving a straight section for 50m before passing under the basement of KFC on 23-24 January 2006. This subtle increase in transverse vibration commenced approximately 1 day before the TBM cutter passed under the basement and remained consistent at less than 0.1mm/s above baseline as the TBM passed under and beyond the tunnel basement, however when the tunnel decreased the radius of turn from >1000m to 220m on or about 6am on 30/1/06, the transverse vibrations became larger and much more distinct despite the cutter face being more than 20m from the KFC basement. As the tunnel passed through the tight radius curve over the period 30/1/06 to 2/2/06 the horizontal plane vibrations increased to approximately 0.35 mm/s above background levels as clearly illustrated in Figure 79 and Figure 80. This was despite the increasing distance from the monitoring point. As the TBM passed out of the tight radius curve after 2/1/06 the horizontal plane vibrations decreased.

P i t d A il 19 2007 (V 7 1 7 1) F t C i ht d 1996 2003 I t t l I

Histogram Start TimeHistogram Finish TimeNumber of IntervalsRangeSample RateJob Number:

11:13:39 January 18, 200618:23:39 January 19, 2006374 at 5 minutes Geo :31.7 mm/s1024sps1

Serial NumberBattery LevelCalibrationFile Name

BE9496 V 7.1-4.35 MiniMate Plus5.7 Volts (Battery Very Low)September 9, 2005 by Standards & Testing Lab.K496AZG1.UR0

NotesLocation: Hungry Jacks BasementClient: LKJV/PTAUser Name:General: Hungry Jacks Basement

Extended NotesMitchell logger BE9496 with Mitchell geophone BG8646

Post Event Notes

PPVZC FreqDateTimeSensorcheck

Tran

0.714>100

Jan 18 /0611:28:39Passed

Vert

0.8107.8

Jan 18 /0611:28:39Passed

Long

0.508>100

Jan 18 /0611:28:39Passed

mm/sHz

Peak Vector Sum 1.19 mm/s on January 18, 2006 at 11:28:39

Monitor LogJan 18 /06 11:13:38 Jan 19 /06 18:23:39 Event recorded. (Battery Low Exit)

0.0Long

0.0Vert

0.0Tran

Jan 18 /0611:23:39

Jan 18 /0615:23:39

Jan 18 /0619:23:39

Jan 18 /0623:23:39

Jan 19 /0603:23:39

Jan 19 /0607:23:39

Jan 19 /0611:23:39

Jan 19 /0615:23:39

Jan 19 /0618:23:39

Time Scale: 10 minutes /div Amplitude Scale: Geo: 0.200 mm/s/div

P i t d A il 19 2007 (V 7 1 7 1) F t C i ht d 1996 2003 I t t l I

Histogram Start TimeHistogram Finish TimeNumber of IntervalsRangeSample RateJob Number:

09:00:06 January 21, 200612:16:04 January 25, 20061191 at 5 minutes Geo :31.7 mm/s1024sps1

Serial NumberBattery LevelCalibrationFile Name

BE9498 V 7.1-4.35 MiniMate Plus6.8 VoltsSeptember 9, 2005 by Standards & Testing Lab.K498AZLF.O60

NotesLocation: Hungry Jack's Basement Client:User Name:General: Hungry Jack's Basement

Extended NotesMinimate #BE9498Geophone #BG8646

Post Event Notes

PPVZC FreqDateTimeSensorcheck

Tran

0.27037

Jan 25 /0602:35:06Passed

Vert

0.36573

Jan 24 /0610:45:06Passed

Long

0.71426

Jan 24 /0616:20:06Passed

mm/sHz

Peak Vector Sum 0.746 mm/s on January 24, 2006 at 16:20:06

0.0Long

0.0Vert

0.0Tran

Jan 21 /0609:30:06

Jan 21 /0621:30:06

Jan 22 /0609:30:06

Jan 22 /0621:30:06

Jan 23 /0609:30:06

Jan 23 /0621:30:06

Jan 24 /0609:30:06

Jan 24 /0621:30:06

Jan 25 /0609:30:06

Time Scale: 30 minutes /div Amplitude Scale: Geo: 0.200 mm/s/div Figure 77 – Baseline Vibrations in KFC Basement Figure 78 - Vibrations due to TBM Passing

Geophone in KFC Basement

Another anomaly noted was the distinct induced building vibrations once the TBM entered to the jet grouted zone and cut against diaphragm wall of the station as shown in Figure 80. The transverse vibrations from the cutter head grinding against the concrete wall can be clearly seen occurring over two shifts on the 5/2/06 and 6/2/06 where small but distinct increases in horizontal vibration of 0.25mm/s occurred. Breakthrough of the TBM cutter occurred on the early morning of 6/2/06, which concurred with the vibration results. Final breakthrough occurred on 7/2/06 which also concurred with a big spike in the vibration data.

In contrast to the vibrations recorded on the predominantly straight southern section, the vibrations on the curved northern tunnel section under Perth Rail Station and Peth Rail Yard were much larger and quite distinct. An example of the vibrations recorded in Perth Rail Yard is discussed in the following paragraphs, with the position of the monitoring point relative to tunnel 1 shown in Figure 81.

P i t d A il 19 2007 (V 7 1 7 1) F t C i ht d 1996 2003 I t t l I

Histogram Start TimeHistogram Finish TimeNumber of IntervalsRangeSample RateJob Number:

12:18:36 January 25, 200611:43:57 February 1, 20062009 at 5 minutes Geo :31.7 mm/s1024sps1

Serial NumberBattery LevelCalibrationFile Name

BE9498 V 7.1-4.35 MiniMate Plus6.8 VoltsSeptember 9, 2005 by Standards & Testing Lab.K498AZT3.J00

NotesLocation: Hungry Jack's Basement Client:User Name:General: Hungry Jack's Basement

Extended NotesMinimate #BE9498Geophone #BG8646

Post Event Notes

PPVZC FreqDateTimeSensorcheck

Tran

0.34947

Jan 30 /0613:03:36Passed

Vert

0.65139

Jan 27 /0608:18:36Passed

Long

0.49218

Jan 30 /0616:43:36Passed

mm/sHz

Peak Vector Sum 0.654 mm/s on January 27, 2006 at 08:18:36

0.0Long

0.0Vert

0.0Tran

Jan 25 /0613:18:36

Jan 26 /0613:18:36

Jan 27 /0613:18:36

Jan 28 /0613:18:36

Jan 29 /0613:18:36

Jan 30 /0613:18:36

Jan 31 /0613:18:36

Feb 1 /0611:43:57

Time Scale: 1 hour /div Amplitude Scale: Geo: 0.200 mm/s/div

P i t d A il 19 2007 (V 7 1 7 1) F t C i ht d 1996 2003 I t t l I

Histogram Start TimeHistogram Finish TimeNumber of IntervalsRangeSample RateJob Number:

11:45:43 February 1, 200614:35:16 February 8, 20062049 at 5 minutes Geo :31.7 mm/s1024sps1

Serial NumberBattery LevelCalibrationFile Name

BE9498 V 7.1-4.35 MiniMate Plus6.8 VoltsSeptember 9, 2005 by Standards & Testing Lab.K498B060.O70

NotesLocation: Hungry Jack's Basement Client:User Name:General: Hungry Jack's Basement

Extended NotesMinimate #BE9498Geophone #BG8646

Post Event Notes

PPVZC FreqDateTimeSensorcheck

Tran

0.31717

Feb 5 /0621:00:43Passed

Vert

0.58743

Feb 7 /0614:25:43Passed

Long

0.5715.4

Feb 7 /0616:25:43Passed

mm/sHz

Peak Vector Sum 0.592 mm/s on February 7, 2006 at 14:25:43

0.0Long

0.0Vert

0.0Tran

Feb 1 /0612:45:43

Feb 2 /0612:45:43

Feb 3 /0612:45:43

Feb 4 /0612:45:43

Feb 5 /0612:45:43

Feb 6 /0612:45:43

Feb 7 /0612:45:43

Feb 8 /0612:45:43

Time Scale: 1 hour /div Amplitude Scale: Geo: 0.200 mm/s/div Figure 79 – Increase in Vibration in Conjunction

with Commencement of Tight Radius Turn by TBM

Figure 80 - Vibration in KFC Basement in conjunction with tight radius turn, and TBM breakthrough.

Figure 81 – Location of Perth Rail Yard Geophone and TBM at First Recorded TBM Vibration

Monitoring Point

Location of TBM 30/5/06, 6:00am

0

1

2

3

4

5

6

7

8

9

10Ve

loci

ty (m

m/s

)

Peak PPV Vertical Vibrations

Reference Baseline

0

1

2

3

4

5

6

7

8

9

10

Velo

city

(mm

/s)

Peak PPV Tranverse Vibrations

Reference Baseline

0

1

2

3

4

5

6

7

8

9

10

26/0

5/20

06 1

2:05

26/0

5/20

06 1

8:05

27/0

5/20

06 0

:05

27/0

5/20

06 6

:05

27/0

5/20

06 1

2:05

27/0

5/20

06 1

8:05

28/0

5/20

06 0

:05

28/0

5/20

06 6

:05

28/0

5/20

06 1

2:05

28/0

5/20

06 1

8:05

29/0

5/20

06 0

:05

29/0

5/20

06 6

:05

29/0

5/20

06 1

2:05

29/0

5/20

06 1

8:05

30/0

5/20

06 0

:05

30/0

5/20

06 6

:05

30/0

5/20

06 1

2:05

30/0

5/20

06 1

8:05

31/0

5/20

06 0

:05

31/0

5/20

06 6

:05

31/0

5/20

06 1

2:13

31/0

5/20

06 1

8:33

1/06

/200

6 0:

331/

06/2

006

6:33

1/06

/200

6 12

:33

1/06

/200

6 18

:46

2/06

/200

6 0:

462/

06/2

006

6:46

2/06

/200

6 12

:46

2/06

/200

6 18

:46

3/06

/200

6 0:

463/

06/2

006

6:46

3/06

/200

6 12

:46

3/06

/200

6 18

:46

4/06

/200

6 0:

464/

06/2

006

6:46

4/06

/200

6 12

:46

4/06

/200

6 18

:46

5/06

/200

6 0:

465/

06/2

006

6:46

5/06

/200

6 12

:46

5/06

/200

6 18

:46

6/06

/200

6 0:

466/

06/2

006

6:46

6/06

/200

6 12

:46

6/06

/200

6 18

:46

Velo

city

(mm

/s)

Peak PPV Longitudinal Vibrations

Reference Baseline

Figure 82 – Measured Peak Vibration Data over 10 days as TBM Approaches and Passes Monitoring Point in Perth Rail Yard

The location of the TBM at 6am on 30/5/06 is also shown in Figure 81 as it concurs with the increase in vibration as the TBM approaches and passes the geophone shown in Figure 82. At this location, the initial deviation from background vibration was observed in the early hours of May 30 as shown on Figure 82., when the TBM was approximately at CH 298 PBup. The 6am position of the TBM was CH 301 PBup on May 30, and thus the approximate range of felt vibrations was 25 metres. This concurred with the experiences on the southern tunnel section. Despite the range of vibrations being similar, the peak vibrations were much greater, approximately 10 mm/s for the northern tunnel versus 0.5 mm/s for the southern tunnel. It is believed that this is consistent with relative effect the tight tunnel radius of 135m versus the minimum 220m radius for the southern tunnel section.

Due to the large period covered by Figure 82, the lack of vibration when the TBM stopped during the ring build phase can not be seen, but when a smaller interval is analysed the distinct lack of vibrations during the ring build phase can be seen as shown in Figure 83.

Figure 84 also details the typical response spectra of the vibrations as the TBM passes the geophone with distinct pulses occurring 2-3 times per second and resultant ground vibration frequencies in the 40-80Hz range. Figures 82, 83 and 84 also highlight the principal direction of wave propagation, with the horizontal waveform being substantially greater than the vertical waveform, with vertical vibrations only noticeable when the TBM is directly under or adjacent the geophone, and the degree of induced vertical vibration remains very small relative to background vibrations from traffic and trains.

Printed: April 19, 2007 (V 7.1 - 7.1) Format Copyrighted 1996-2003 Instantel Inc.

Histogram Start TimeHistogram Finish TimeNumber of IntervalsRangeSample RateJob Number:

11:18:42 May 31, 200614:47:07 May 31, 200641 at 5 minutes Geo :31.7 mm/s1024sps1

Serial NumberBattery LevelCalibrationFile Name

BE9498 V 7.1-4.35 MiniMate Plus6.8 VoltsSeptember 9, 2005 by Standards & Testing Lab.K498B6AC.R60

NotesLocation: Railyard (under 1st Aid)Client: LKJVUser Name:General:

Extended NotesTBM MonitoringGeophone #BG8646

Post Event NotesVIBRATION DUE TO TBM IN CLOSE PROXIMITY. SENSOR AT CH 321 PBup. CUTTER FACE AT CH 318 PBup AT 12:00

PPVZC FreqDateTimeSensorcheck

Tran

6.6739

May 31 /0611:58:42Disabled

Vert

1.5764

May 31 /0612:03:42Disabled

Long

5.9457

May 31 /0613:28:42Disabled

mm/sHz

Peak Vector Sum 7.16 mm/s on May 31, 2006 at 11:58:42

0.0Long

0.0Vert

0.0Tran

May 31 /0611:23:42

May 31 /0613:23:42

May 31 /0614:43:42

Time Scale: 5 minutes /div Amplitude Scale: Geo: 1.000 mm/s/div

Printed: April 19, 2007 (V 7.1 - 7.1) Format Copyrighted 1996-2003 Instantel Inc.

Date/TimeTrigger SourceRangeRecord TimeJob Number:

Tran at 15:08:57 May 31, 2006Geo: 3.00 mm/sGeo :31.7 mm/s9.0 sec at 1024 sps1

Serial NumberBattery LevelCalibrationFile Name

BE9498 V 7.1-4.35 MiniMate Plus6.9 VoltsSeptember 9, 2005 by Standards & Testing Lab.K498B6AN.EX0

NotesLocation: Railyard (under 1st Aid)Client: LKJVUser Name:General:

Extended NotesCombo Mode May 31, 2006 15:03:10TBM MonitoringGeophone #BG8646

Post Event NotesVIBRATION DUE TO TBM IN CLOSE PROXIMITY. SENSOR AT CH 321 PBup. CUTTER FACE AT CH 318 PBup AT 12:00,CUTTER @ 320.5 @ 18:00 31/5

PPVZC FreqTime (Rel. to Trig)Peak AccelerationPeak DisplacementSensorcheck

Tran

3.0847

0.0010.0795

0.00939Disabled

Vert

0.88964

0.0190.0348

0.00388Disabled

Long

1.9764

0.0190.0878

0.00554Disabled

mm/sHzsecgmm

Peak Vector Sum 3.10 mm/s at 0.001 sec

USBM RI8507 And OSMRE

Velo

city

(mm

/s)

Frequency (Hz)

1 2 5 10 20 50 1001

2

5

10

20

50

100

200254

Tran: + Vert: x Long: ø

+

+ ++

++++

+ +++

++

++

+

++

+++ +++

+

+++

++++

+++

+

+++

+ ++

++

+

+++

++ø

øø

øø ø

øøøøøø

øø øø

øø øøøø

øøøøøøøø

ø

øøø ø

øøøøøøøøøøøø

øøøøøø

øø

øøø

ø

øø ø

øøøøøø

øøøø

øø

øøø ø

øøøøøø

øøøø

>

0.00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

Trigger =

0.0Long

0.0Vert

0.0Tran

Time Scale: 0.50 sec/div Amplitude Scale: Geo: 1.000 mm/s/div

Figure 83 - Detailed Vibration Response during Tunnelling and Ring Build Stages

Figure 84 - Typical Response Spectra and Waveforms from TBM vibrations

Similar vibrations were expected on the second tunnel run in Perth Rail Yard, and monitoring was configured accordingly. However, field observations indicated that vibration was not consistent and varied from being distinct one day to indiscernible the next, despite no changes in tunnelling. These observations were confirmed by monitoring at additional locations in the Perth Rail Yard and Perth Rail Station. Measurements were also taken at the same location as for Tunnel 1 and did not show the

build up in vibrations as seen in the first tunnel run. Thus it can be concluded that whilst vibrations are clearly a function of turning radius, the vibrations can not be reliably predicted to occur. Given this evidence, the detailed response spectra, and feedback from tunnel crew, it is concluded that the TBM cutter is not the likely source of any vibration in the sandy soils, rather the perceived caused of the vibration is the pulse of the tail void grout as squeezes in between the outside of the shield and the surrounding soil, and/or the ring grease injection as it squeezes between the inside of the shield and the as built rings due to the tight space between the shield and the constructed rings.

5.7 Settlement due to Sheet Pile Extraction

During design, it was anticipated that ground movement caused by extraction of the sheet piles would be relatively minor and would typically lead to settlement of about 10 to 15 mm. This movement was allowed for when using an empirical method to estimate ground surface settlement behind a retaining structure.

Measurements of ground surface settlement in response to sheet pile extraction were undertaken at the TBM Launch Box, Esplanade Station, Foreshore Area 2, Foreshore Area 7 and Perth Yard Receival Box/ Cut and Cover Areas. Significant surface settlements in response to sheet pile removal were noted, especially in close proximity to the sheet piles. The measured surface settlements from all the areas are shown in Figure 85. The results were consistent across each of the areas and do not appear to be dependent on geology.

Analysis of the data indicates that the average volume of the settlement depression is approximately 0.46 m3 per metre length of wall, as calculated from the fitted curve shown in Figure 85. For volume comparison and using a nominal 20m long sheet pile, the notional volumes of PU18, PU25, and PU32 sheet pile wall are 0.33, 0.40 and 0.48 m3 per metre length of wall respectively. Thus the average volume loss on this project is slightly greater than the volume of the sheet piles that were extracted on the project (PU 16, 20, 24 and 32 were used). This additional volume loss was expected as some material stuck to each of the sheets on removal and thus contributed to the additional volume loss.

y = 32.615Ln(x) - 90.933Volume = 0.46 m3 per metre of wall

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

00 5 10 15 20 25 30

Distance from Sheet Pile (m)

Gro

und

Mov

emen

t (m

m)

Launch Box North Wall Esplanade StationForeshore Area 2 Perth Rail YardFreeway DiveLog.

Range of volume loss = 0.22 to 0.75 m3 per metre of wall

Figure 85 - Surface Settlement Due to Extraction of Sheet Piles.

Thus a empirical relationship for from estimating volume loss and ground settlement in response to sheet pile removal is proposed, whereby the predicted volume loss is equivalent to volume of sheet pile removed multiplied by an appropriate factor to account for soil adhesion. This factor is an estimate at present, with experience on the project indicating it could vary between 1 and 2.

The expected shape of the settlement curve would be in the form shown in Figure 86 and can be determined using Figure 87 and the method described below: It should be noted that this relationship is notionally only valid for predicted volume losses between 0.1 and 1.0 m3 per metre of wall.

Step 1: Determine the cross sectional area of the pile per metre length of wall, X. i.e. PU 32 =0.242m2

Step 2: Determine the length of the pile, L. i.e. 20m

Step 3: Determine the volume of sheet pile per metre of wall, VP= X * Y = 0.48 m3.

Step 4: Allow for adhesion factor (f) of say 1.5, then Expected Volume Loss, VL = VP * f = 0.72 m3 per metre length of wall.

Step 5: Determine the Settlement Curve parameters A and B from Figure 86 or via the equation

A = VL / [0.0075*LN(VL) + 0.0199] and B = A*[0.5331*LN(VL) + 3.1597]

Thus for 0.72m3, A= 41.3, and B = 123.2.

Step 7: Plot the expected Settlement Curve in the form Settlement (mm) = A* Ln (m) - B, where m is the distance from the wall in metres. An example of the predicted settlement curve due to sheet pile extraction for a 20m long PU 32 sheet pile is shown in Figure 87.

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0 0.2 0.4 0.6 0.8 1

Volume Loss (m3) per metre width of wall

Vol

ume

Loss

/ A

2

2.4

2.8

3.2

3.6

40 0.2 0.4 0.6 0.8 1

B /

A

Volume/A B/A Log. (B/A) Log. (Volume/A)

Figure 86 - Ground Settlement Curve Parameter Determination

20m Long PU 32 Predicted Settlement Curve

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

00 5 10 15 20 25 30

Distance from Sheet Pile (m)

Gro

und

Mov

emen

t (m

m)

Figure 87 - Example Ground Settlement due to Sheet Pile Removal Prediction

6 SUMMARY

Instrument and Monitoring on the New MetroRail – City Project was a complex and difficult task requiring a high degree of technical and management skill. In order to achieve this a management approach focussed on outcomes and reasons for monitoring was adopted together with the production and use of detailed management plans to ensure that feedback to all parties was being achieved in a timely and productive manner whilst ensuring the safety of all personnel on the project and the surrounding public.

Significantly higher quantities of instrumentation were installed above to the minimum quantities specified in the SWTC to ensure the quality of the output was meaningful, and could be used by all parties to monitor the project progress. The regular high quality output produced, and ongoing feedback by the monitoring team was a prime factor in the high standard of construction results achieved on the project especially with respect to the world’s best practice tunnelling results.

A high degree of automation was also used on the project to ensure cost effective quality monitoring could be achieved on sensitive buildings and heritage structures. The lessons learnt from the project clearly indicate that automated EL Beams and Prisms are the most cost effective, reliable and accurate means of monitoring ground and building movement and should be adopted as minimum requirements on similar tunnelling and/or construction projects. Automated groundwater and structural monitoring was also found to be highly cost effective, reliable, and accurate, providing substantially greater detail on ground and structural response than any manual instrument. The use of manual surveying and monitoring methods should only be used for very small projects, or as a control and redundancy measure for automated instruments on larger projects.

Innovative methods were also developed on the project to tackle difficult situations and/or save on time and money, whilst other new innovations were adopted and used with great success. These were:

• Vacuum extraction drilling; which was found to be extremely quick and cost effective means of installing deep settlement points and forming shallow excavations.

• Vibratory probing with a small Geo-Probe rig was used to achieve continuous coring to 20+ metres and to install high quality piezometer nests being achieved in less than half the time and cost of traditional methods.

• An innovative piezometer installation method was also developed to ensure high quality installations which isolate the aquifer being monitored, and also allows for determination of the degree of hydraulic confinement of the aquifer being monitored. The installation method also allows for retrieval of automated piezometers at the end of the project.

• The sonic coring method, which was new to Perth, was used with great success to install inclinometers, core pavements and continuously sample jet grout and soil mix columns which are normally extremely difficult to recover, whilst achieving minimum disturbance or environmental impact.

• Wireless EL beams and Tilt Meters were also adopted and found to have accuracies so small and sensitive that the building response to earthquakes more than 5000 km could be detected. The frequencies used on the projects also extended the known range of these instruments by several hundred metres.

• Photogrammetry, with auto-target recognition software was also used with success on the project, adding to the quantity of data obtained on a busy 4 lane road, whilst reducing the survey time and reducing the risk to survey personnel

The monitoring on the project also highlighted a number of phenomena associated with construction and tunnelling which are applicable to similar projects and should be noted. The main findings were:

• Vibration due to EPB tunnelling in sandy and sandy clay materials is predominantly due to turning radius and vibrations in straight driving could be determined. The depth of cover was also found to be unrelated to the degree of vibration. The predominant direction of induced vibration was horizontal, with induced vertical vibrations being very small even in tight radius turns.

• Numerical Modelling was found to be inadequate in modelling the effect of construction traffic adjacent excavations and a nominal 40-50mm should be allowed for traffic consolidation when predicting settlements adjacent large excavations.

• Numerical modelling was found to be poor at estimating lateral movements and settlements due to excavations in cantilever and caution needs to be adopted when using the results of these models in these cases.

• Acceptance Criteria and/or Alert Levels should not be based on a percentage of the design value, i.e. 80%, 100% or 120%, rather, the acceptance criteria should be based on a the design value plus a percentage of maximum design value, i.e. maximum allowable = design value + 20% of maximum value). An empirical relationship illustrating a predicted maximum settlement curve incorporating consolidation due to construction traffic was developed.

• Numerical predictions of settlement and lateral deformation using undrained parameters were found to be very distant from reality, thus not fit for purpose. This is due to the rapid increase in strain and deformation associated with deep excavations resulting in the rapid transformation to drained condition.

• Deformations and settlements due to the installation of preventative TAM grouting can be greater than that due to tunnelling. Detailed management of the installation process is required and should not be left to the contractor alone. The installation density of TAM pipes was found to be directly related to induced settlements.

• Jet grouting can be very successful in improving sands with minimal heave if procedures on curing are followed. It was found that adjacent jet grout columns should not be jetted within 2 days of each other, otherwise excessive heave would develop. If this procedure was followed it was found that very minimal increases in heave occurred. The soil mix and jet grouted blocks were also found to be very effective in providing ground and pressure control as the EPB TBM departed and entered the stations.

• A relationship between the trough width parameter “K” in volume loss predictions and the depth of cover was observed. The process of superposition of predicted gaussian settlement troughs was shown as valid.

• Tunnelling with soil cover of less than 0.5 Tunnel Diameters can be achieved with minimal settlement when high quality tunnel management and expertise is combined with high quality monitoring.

• A relationship between sheet pile removal and ground settlement was observed, and a empirical relationship was developed to predict the ground settlement curve due to sheet pile removal This relationship is applicable to other sites and can be used as a predictive tool for future construction projects.

An excellent result was achieved in terms of construction success and public image on the project due to the high degree of quality monitoring and the effort put in by the monitoring team.

7 REFERENCES

Boscardin, M.D., and Cording, E.G., 1989. Building Response to Excavation Induced Settlement. Journal Geotechnical Engineering, ASCE, vol 115.

Burland, J.B., 2001 Assessment Methods Used in Design. In Building Response to Tunnelling – Case Studies from Construction of the Jubilee Line Extension, London. Vol 1, Chp. 3 pp 23-44.

McGough, P.G., 2007. Thermal Calibration of Strain Gauges. Proc. 10th Australia New Zealand Conference on Geomechanics, Brisbane, 21-24 October 2007.

Nobes, C., & Williams, M., 2007. Compensation Grouting for Building Protection. Proc. Seminar on New MetroRail City Project, Tunnelling and Structures, Perth, 13 September 2007.

Peck, R. B., 1969. Deep Excavations and Tunnelling in Soft Ground - State of Art Report, 7th Int Conference SMFE, Mexico.

Sigl, O., Nobes, C., McGough, P.G., 2007a. Jet Grouting. Proc. Seminar on New MetroRail City Project, Tunnelling and Structures, Perth, 13 September 2007.

Sigl, O., Aikawa, F., Amon, A., Bo, H., and Stewart, D., 2007b. Temporary Strutted and Anchored Sheet Piling. Proc. Seminar on New MetroRail City Project, Tunnelling and Structures, Perth, 13 September 2007.