This Compilation of TAC Papers was prepared courtesy of

The Niagara Tunnel Project - An Overview

Russel Delmar, P.Eng.

Construction Manager, Hatch Mott MacDonald, Niagara Falls, ON, Canada

Harry Charalambu, P.Eng.

Project Manager, Hatch Mott MacDonald, Niagara Falls, ON, Canada

Ernst Gschnitzer, Ph.D.

Project Manager, Strabag, Niagara Falls, ON, Canada

Rick Everdell, P .Eng.

Project Director, Ontario Power Generation, Toronto, ON, Canada

Abstract:

The award of the design build contract for construction of Ontario Power Generation's (OPG)

Niagara Tunnel Project was made on September 1, 2005, after an eight month international

procurement process. The project requires delivery of a nominal 500 m3/s of water from the

Niagara River from an intake located upstream from Niagara Falls via a 10.4 km tunnel running

underneath two existing water delivery tunnels beneath the City of Niagara Falls, to an outlet at

the existing Sir Adam Beck generating station complex. The tunnel will be excavated by means

of the world's largest hard rock TBM, a 14.44m diameter open gripper machine. Vertical

alignment of the tunnel is constrained by an ancient buried gorge at the north end and existing

abandoned power generating facilities at the south end. Approximately 80% of the tunnel will be

in Queenston Shale, which exhibits both squeezing and swelling characteristics. The tunnel lining

will be a two-pass system with rock bolts, mesh, steel ribs and shotcrete as the primary lining and

cast-in-place concrete, with a double layer waterproofing membrane, as the final lining. Under the

contract, subsurface geotechnical risk is assigned by means of a negotiated Geotechnical Baseline

Report (GBR).

Keywords: stakeholders to the Niagara tunnel project; mandatory requirements and liquidated

damages/bonuses; construction schedule; geotechnical baseline report; scope of work; intake;

outlet; Cambrian, Ordovician and Silurian Sedimentary rocks; tunnel construction sequence;

tunnel lining; initial lining; support for rock; final lining; waterproofing membrane system;

contact grouting; interface grouting.

Delmar, R., Charalambu, H., Gschnitzer, E., Everdell, R. The Niagara Tunnel Project - An Overview. 2006 Tunnelling Association of Canada Proceedings.

The Niagara Tunnel Project - An Overview

Russel Delmar, P.Eng. Construction Manager, Hatch Mott MacDonald, Niagara Falls, ON, Canada

Harry Charalambu, P.Eng. Project Manager, Hatch Mott MacDonald, Niagara Falls, ON, Canada

Ernst Gschnitzer, Ph.D. Project Manager, Strabag, Niagara Falls, ON, Canada

Rick Everdell, P .Eng. Project Director, Ontario Power Generation, Toronto, ON, Canada

ABSTRACT: The award of the designlbuild contract for construction of Ontario Power Generation's (OPG) Niagara Tunnel Project was made on September 1, 2005, after an eight month international procurement process. The project requires delivery of a nominal 500 m3/s of water from the Niagara River from an intake located upstream from Niagara Falls via a lO.4~km tunnel running underneath two existing water delivery tunnels beneath the City of Niagara Falls, to an outlet at the existing Sir Adam Beck generating station complex. The tunnel will be excavated by means of the world's largest hard rock TBM, a 14.44·m diameter open gripper machine. Vertical alignment of the tunnel is constrained by an ancient buried gorge at the north end and existing abandoned power generating facilities at the south end. Approximately 80% of the tunnel will be in Queenston Shale, which exhibits both squeezing and swelling characteristics. The tunnel lining will be a two-pass system with rock bolts, mesh, steel ribs and shotcrete as the primary lining and cast-in-place concrete, with a double layer waterproofing membrane, as the final lining. Under the contract, subsurface geotechnical risk is assigned by means of a negotiated Geotechnical Baseline Report (GBR).

I THE NIAGARA RIVER - WATER DIVERSION AND GENERATION CAPACITY

1.1. Introduction The Niagara River is an international waterway fonning part of the boundary between Canada and the United States of America. The river is about 53 kilometers (lan) in length with an average flow of approximately 6000 cubic metres per second (m'/s).

The hydroelectric resource at Niagara is shared with the United States of America in accordance with the tenns of the 1950 Niagara Diversion Treaty. This treaty established priority for scenic, domestic and navigation purposes and allows the remaining flow to be used for power generation. The scenic flow requirement is 2832 m'ls during the daytime from April through October and 1416 m'ls at all other times. About two-thirds of the average Niagara River flow is available for power generation and is shared equally by Canada and the United States.

1.2. Developing More Power In the 1980's, Ontario Hydro, the predecessor to Ontario Power Generation (OPG), began exploring the possibility of developing more power at the Sir Adam Beck (SAB) Niagara generating complex.

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Preliminary engineering and an environmental assessment (EA) were undertaken on the proposed new Niagara River Hydroelectric Development (NRHD). The NRHD EA was approved by Ontario's Ministry of Enviromnent in October 1998. The approved project included construction of two additional diversion tunnels and an underground generating station north of the existing SAB generating stations.

Table l. Diversion and Generation Capacities

In-Service Diversion Station Annual Year Capacity Capacity Energy

(m'/s) (MW) (GWh) SAB 1 1922 625 487 2,700 SAB2 1954 1,200 1,472 9,200 SABPGS 1958 122 100 Current Totals 1,825 2,081 11,800 Niagara Tunnel 2009 500 1,600 Future Totals 2,325 2,081 13,400

In July 2004, OPG decided to proceed with the Niagara Tunnel Project, a designlbuild project for one of the diversion tunnels. This tunnel will divert a nominal 500 m'ls of water to OPG's SAB Generating

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Station complex allowing more efficient use of the Niagara River flow available to Canada for power generation, facilitating an increase in average annual energy output of about 1600 GWh (14%), which is enough to supply the annual needs of a city of approximately 160,000 residents. The second diversion tunnel and underground powerhouse could be constructed in the future, depending on energy requirements and project economics. I

The flow in the Niagara River that is available to Canada for power generation varies from about 1000 m'/s to 3000 m'/s and as indicated in Figure I, exceeds the existing SAB diversion capacity (canal and two tunnels) about 65% of the time. With the addition of a nominal 500 m'ls diversion capacity from the new tunnel, the available flow will exceed SABs diversion capability only about 15% of the time.

Niagara Rjvcr .OPO;> En(d!emen! _ Monthly flow Dunrtion Curvo P«iO<t.llfl1n6·0<02003

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Fig. 1. Water Availability in the Niagara River

2 THE NIAGARA TUNNEL PROJECT -DESIGNIBUILD PROPOSAL PROCESS

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In July 2004, OPG decided to proceed with Phase 1 of the Niagara Tunnel Project which was to procure a contractor based on the following objectives: • to minimize the project duration • to capture contractor experience and innovations • to appropriately allocate project risks • to provide as much price certairity as possible.

It was, therefore, decided to proceed with a design/build process as this was considered the best approach to achieving these objectives. The proposal process included a number of distinct stages: • an international invitation for expressions of interest • a prequalification process • proposal preparation and submission • proposal evaluation and negotiation culminating in

the award of a designibuild contract.

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Of the seven contractors that submitted expressions of interest, four were pre-qualified to submit proposals on the basis of a number of evaluation criteria that included relevant design and build experience and safety performance. Three proposals were received after a five month proposal period and this was followed by proposal evaluation and negotiations with all three proponents. Evaluation criteria included the design and construction approach, cost, risk profile, tunnel flow capacity, schedule, project team, health & safety management, environmental management and quality management. A recommendation of a designlbuild contractor was made to OPG Board of Directors in July 2005 and the project was approved by OPG and the Government of Ontario by August 17,2005.

Phase 2, the detailed design and construction of the project, commenced on August 18, 2005, with the award of the design/build contract to Strabag AG of Austria with local sub-contractor, Dufferin Construction, assisted by designers ILF from Austria and Morrison Hershfield of Toronto.

2.1. Stakeholders to the Niagara Tunnel Project A number of stakeholders, as summarized in Table 2, will influence the successful completion of the project.

Table 2. Key Stakeholders

Stakeholder Responsibility OPG Shareholder

Government of Ontario Provide Direction to OPO

-""6'~neriop'eraior""'"""'-'''""-and Financing .............. .. __ "._

... "Proy""id"e-Proj'ect 'Direction and Oversight OPGfNiagara Plant

Group Operate and Maintain New Tunnel and Gates

·· .. O;ner·;·s .. ·R'ep"reseni"atl've .... · ""''''''Admini'ster''i5esl'gnJfiu'fid'''" Hatch Mott MacDonald Contract with Hatch Acres Review Design and Monitor

Construction -j)-esignlBuilct Contractor Execute DesignfBuiid

Strabag AG Contract -Regulato'rs-"--------;Mc-i'o"'n~ito.::r:::C;-o-m-p-;Ji~a-n-ce-w~it:ch-

MOE, MNR, DFO, EA Approval NPCA Issue Permits/Certificates

~,--~c.~~~:c-___ ~o,,-,f Approval _.~=--~ __ Host Municipalities Manage Forecast Tourism

Niagara Region Impacts Niagara Falls Provide Agreed Municipal Niagara~on-the~Lake Services

Issue Municipal Petmits

The Ontario Government, as OPG's sole shareholder and project financier, endorsed and approved the project as being consistent with its objective of promoting the development of cost competitive, environmentally friendly sources of

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electricity generation. OPG and its Niagara Plant Group (NPG) are the Owner and facility Operator respectively. OPG selected Hatch Mott MacDonald in association with Hatch Acres as its Owner's Representative to administer the design/build eontraet and provide engineering review and construction monitoring services. Strabag AG from Austria was awarded the designJbuild contract. A number of regulatory agencies are responsible for monitoring the terms of the Environmental Assessment Approval and for issuing permits. In addition, the projeet is hosted by a number of local municipalities that include the Regional Municipality of Niagara, City of Niagara Falls and Town of Niagara -on-the-Lake.

A Community Impact Agreement (CIA) was signed in December 1993, between Ontario Hydro (~ow OPG), the Regional Municipality of Niagara, the City of Niagara Falls, and the Town of Niagara-on­the-Lake. The CIA outlines eompensation for anticipated project impacts, and addresses: • Municipal Approvals • Liaison Committee • Monitoring and Remedial Programs • Tourism Impact Management • Transportation Impact Management • Municipal Sewage Collection and Treatment • Municipal Water Supply • Municipal Garbage Disposal • Emergency Services (where permitted and cost

effective).

Milestones "

3 DESIGNIBUILD CONTRACT

3.1. Mandatory Requirements and Liquidated Damages/Bonuses

Proposals for the Niagara Tunnel Project were based on an invitation for proposal document that mandated a number of key technical requirements including: • construction of a 10.4-km long TBM driven tunnel

from an outlet on OPG property near the existing SAB generating stations, along a mandated horizontal alignment, to an intake in the Niagara River

• design life of the fueility to be 90 years including measures to deal with swelling rock conditions in the local shale units

• tunnel to deliver a nominal 500 m'ls water flow. For construction scheduling, the Invitation

required contractors to propose substantial completion dates which were then taken into account during proposal evaluation (earliest substantial completion was evaluated most beneficially). This date was then used as the contractual substantial completion date for the successful contractor. Similarly, proponents were required to propose a guaranteed flow amount, based on the prevailing hydraulic heads and their selected tunnel diameter and final lining characteristics. These flow amounts were also taken into account during proposal evaluation (largest guaranteed flow amount was evaluated most beneficially) and this flow amount was then adopted as the contractual guaranteed flow amount. The contract includes bonuses for exceeding the guaranteed flow amount and for early substantial completion, and liquidated damages for failure to achieve the same.

3.2. Construction Schedule A summary level project schedule is provided in Figure 2.

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Fig. 2. Summary Schedule for the Niagara Tunnel Project

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3.3. Geotechnical BaseNne Report The geotechnical baseline report (G BR) was produced by means of a nego tiated process whereby: • an initial GBR (G BR-A), prepared by OPG, was

included in the Invitation that allowed proponents to revise the GBR as required to suit their proposed means and methods.

• a proposal, GBR (G BR-B) submitted with the proponents proposal and reviewed and evaluated as part of the proposal evaluation with changes made during the negotiation process.

• the fina l negot ia ted GBR(C) (the GBR) was then included in the designlbu ild contract.

3.4. Scope of Work The project comprises three major clements of work, namely, Intake fac il it ies, Outlet facilities and Di version Tunnel.

Intake The tunnel Intake facilities consists of a submerged re inforced concrete bell-mouth intake structure in the Niagara River, beneath Bay I of the existing Interna tional Niagara Control Works (fNCW) structure, and a 170 m long underwater approach channel in the river bed. The intake structure

accommodates sectional gates for closure of the tunnel when required for dewatering. To facilitate construction of the In take in the dry, a temporary cofferdam will be installed upst ream from Bay 1. Extensive curta in grouting o f the high ly permeable bedrock fornlations will be required prior to drill and blast excava tion down to tunnel invert e leva tion, a depth of approximately 40 111. A 5 m minimum diameter x 250 111 mini mum length grouting ga llery will be drill and blast excavated a long the diversion tunnel axis to enable pre­grouting prior to arriva l of the TBM. Depending on Intake works productivity, schedule, design, envi ronmental and logistica l considerations, a fu ll diameter grouting ga llery may be excavated thereby reduc ing critical path TBM tunnelling. Other work at the Intake inc ludcs removal of an exis ting 520-111 long ice accelerat ing wall that extends upstream from Pier 4 of the (NeW structure and insta llat ion of a para llel new precast concrete accelerat ing wall upst ream of Pier 5. A new 360-m long precast concrete approach wall wi ll also be constructed along the shoreline. Work on the approach channel, accelerat ing and approach walls will be carried out as a marine-based operat ion.

Fig. 3. Niagara Tunnel Project - Elements and Layout of the Work

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Outlet The tunnel Outlet consists of a reinforced concrete outlet structure discharging into a 390 m long canal, excavated in rock, connecting to the existing Pump Generating Station canal near the SAB Generating Stations. A closure gate and hoist will be provided at the Outlet to permit closure of the tunnel for emergencies and for dewatering. During construction, the outlet canal also acts as the. assembly and launch site for the TBM and as the staging area for logistics to and from the bored tunnelling operation. A 40 m long rock plug, between the new and existing PGS canal, will be left in place for the duration of construction. One of the final construction activities will be removal of this plug at the time of watering up of the tunnel.

Diversion Tunnel The approximately 10A-km long Diversion tunnel will be constructed as a two-pass tunnelling system with boring taking place from the Outlet canal to the Intake excavation. A 14.44 m diameter Robbins open gripper rock machine will be used. This will be the largest diameter rock machine in the world to date. An initial rock support lining will be installed from the TBM and trailing gear followed by an in­situ placed concrete lining after completion ofTBM tunnelling. Approximately 1.7 million cubic metres of excavated spoil material will be transported from the TBM by conveyor belt and disposed on OPG property between the two existing power canals. Five dewatering shafts of 0.75 m diameter will be constructed at the lowest point of the tunnel to allow tunnel dewatering if required.

3.5. Geology The Niagara Region is underlain by Cambrian, Ordovician and Silurian sedimentary rocks having a total thickness of app(oximately 800 to 900 m. The Niagara River Gorge, the main physiographic feature, and the Niagara Escarpment control the topography of the project area. The generally flat lying bedrock strata consists of dolostone, dolomitic limestone, sandstone and shale in which the diversion tunnel will be excavated with about 80% of the tunnel length in the Queenston Formation, a siltstone/mudstone with an unconfined compressive strength ranging from 19 to about 45 MPa.

The present Niagara River Gorge was formed by erosion during the last major ice retreat, about 12,000 years ago. The buried St. Davids Gorge represents an earlier river course that has been in­filled with glacial outwash materials. Away from the gorge areas, the bedrock is covered almost entirely by glacial lake sediments.

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The buried St. Davids Gorge is similar in shape to the Niagara River Gorge and extends from Lake Ontario through the village of St. David's to the Whirlpool. The St. Davids Gorge is oriented in a northwest direction and varies in width from 350 to 630 m in the vicinity of the Niagara River. Depth to bedrock is in the order of 125 m in the vicinity of the proposed tunnel alignment and in excess of 200 m where it intersects with the present Niagara River at the Whirlpool. The gorge is completely in­filled with deposits of glaciolacustrine, glacial and glaciofluvial origin. The bedrock (Queenston Formation) over the width of the St. Davids Gorge is slightly weathered and relatively more fractured to a depth of between 15 to 25 m below the bottom of the gorge. Below this depth, the rock is generally fresh and of excellent quality.

Bedrock in the project area has generally well­defined bedding with a southerly dip of about 6m1km and an east-west strike. Sheared, weak bedding planes exist between many of the rock formations and within the Queenston Formation. There are. no known occurrences of any major faulting within the project area, some near-surface thrust with minor vertical displacement are known to occur and are probably related to stress relief associated with the gorge formation and the high horizontal residual stresses in the area. Some shearing of this type is expected in the area of the St. Davids Gorge. Three major near-vertical joint sets, which strongly influenced the physiography of the project area, have been identified. These sets strike parallel to the Niagara River; the St. Davids Gorge and the Niagara Escarpment. Vertical joints are generally widely spaced. The joint surfaces are generally rough and fresh to slightly weathered.

3.6. Bedrock Stratigraphy and Structure In descending order from surface, the sequence of rocks is as presented in Table 3.

The Queenston Formation extends well below the deepest section of the tunnel with thickness greater than 300 m being reported in the literature.

Primary bedding planes are defined as major bedding planes between lithological units above the Queenston Formation and between sub-units within the Queenston Formation. Sheared primary bedding planes refer to those planes where some differential displacement has occurred. Within the Queenston Formation, the primary bedding planes are major discontinuities occurring at spacing of about 5 m to somewhat greater than 20 m and locally affecting the rock mass quality.

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Table 3. Rock Sequence to be Encountered During Tunnelling

Sequence DescriEtion Thickness Guelph Dolostone 2 t03 m Lockport Dolostone 43 to 45 m DeCew Dolostone 2 to 3m Rochester Shale 17to 19m Irondequoit Limestone 2 t04m Reynales Dolostone 3.5 to 4.5 m Neahga Shale 1.5 to 2 m Thorold Sandstone 2 to 3.5 m Grimsby Sandstone 12.5 to 15m Power Glen Shale IO to 12 m Whirlpool Sandstone 4.9 to 8.5 m Queenston ShalelMudstone >300m

These planes often exhibit features such as gouge or breccia (a rew millimetres to 2 to 3 em) and slickensides that are consistent with lateral structural dislocation.

Groundwater conditions in the project area are influenced by depth and lithology, and vary between the rock formations above the Queenston Formation, but are relatively consistent in the Queenston Formation. The only.known aquifers are the Lockport and DeCew (dolostone) Formations, whereas the remaining strata below the DeCew are generally considered to be aquitards. Hydraulic conductivity ranges from <10" to 10-3 cmls in the upper dolostone and limestone formations and from 4 x 10'3 cmls to practically impermeable «10" cmls) in the shale formations. In general, the groundwater below the DeCew Formation is highly corrosive.

Natural gas has been encountered in some of the formations, particularly in the Rochester and Grirnsby Formations, with some minor amounts of gas being encountered in other formations, including the Queenston.

High in-situ stresses exist in the project area bedrock. Measurements along the tunnel horizon show that maximum horizontal stress in the Queenston Formation range from 10 to 24 MPa, with a maximum horizontal/vertical stress ratio varying from 3 to 5. In general, the orientations of the maximum horizontal stresses along the alignment of the diversion tunnel lie within the NE­SW quadrant. The orientations of the local stresses are influenced by the presence of major physiographic features, namely the buried St. Davids Gorge and the Niagara River Gorge.

The formations in the project area are subject to time-dependent deformations, initiated by the relief of the relatively high in-situ stresses and swelling on the uptake of fresh water. There is a well-

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documented history of rock "squeeze" affecting surface excavations. The swelling potential of shale units in the Niagara area is also well documented. Swelling involves the volume increase in shale units and is initiated by the relief of the high in-situ stress in the presence of freshwater. The process is associated with chloride ion diffusion from the connate pore water in the rock.

4 TBM, TRAILING GEAR AND BACKUP EQUIPMENT

Strabag selected a Robbins Open Gripper TBM for the project. The machine, with specifications as reflected in Table 4, was fabricated in a number of countries including the USA (predominantly in Robbin's factories in Ohio), England (Markham facilities), Canada and Europe.

Table 4. TBM Specifications

__ .,Q,"~!'!ip~ion_, ___ Deta~~, .. ____ ._ HARD ROCK TBM - DESCRIPTION

Machine Diameter New cutters 14.44

(worn cutters) 14.41 Main Bearing - three roller (3 axis)

Bearing life > 13,000 Ll 0 hrs @ 224

Cutters Number of cutters

Loading Individual cutter load

kN cutter load

85 x 19"/20" (483/508 mm)

311 kN Average cutter spacing 89 mm

Cutterhead - Recommended Operating Cutterhead thrust 18,426 kN Maximum thrust 27,900 kN

Maximum IQipper force 71,500 kN Cutterhead Drive - Variable Frequency Description Cutterhead

Drive/Electric Motors/Gear

Cutterhead power Cutterhead Torque

at 2.4 rpm at 5.0

Breakout Torque Thrust Cylinder Stroke

Transformer (TBM Drives)

Transformer Backup

RedueersNF Drive 15x315 kW = 4,725 kW

18,670 kNm 8,960kNm 28,000 kNm

1.82 m 2 x 2500 kVA

I x 1000kVA

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Description

Capacity Belt width

Conveyor

TBM weight (approx.)

Details

1600 tph 1400 mm

1900 t

The trailing gear was manufactured by ROWA of Switzerland with fabrication carried out in Slovenia and Hungary. Additional backup equipment such as the muck conveyor was procured from H+E Logist ics of Gemlany, the rubber tired transporters from Plan and Teco of Gemlany and ventilation equipment from Cogemacollstic of France.

5 TUNNEL DESIGN AND CONSTRUCTION

5./. Alignment Constraints Vertical alignment of the tunnel, as reflected in Figure 5, is constrained by a number of existing s tructures and geological features. In profile, at the north end the tunnel passes beneath the buried SI. Davids Gorge with bedrock at an approximate elevation of 100 m. This requires an initial tunnel downgrade of 7.82% from the Outlet portal to pass beneath the buried gorge with minimum rock cover of approximately 10 111. At this lowest point the tunnel axis is approximately 135 111 below ground surface.

Progressing southward, the tunnel rises at an upgrade of 0.1% to a point beneath the existing diversion tunnels I and 2 where the cover between new and existing tunne ls is approximately 24 m. In this vicinity the tunnel also croSSC$ under the decommissioned Toronto Power Station which features a 50 111 dcep turbine pit and tailrace tunnels. From these crossings the tunnel rises at an upgrade of7.15% to the Intake portal beneath Bay I of the INCW structure. These alignment constraints result in the tunnel being located predominantly in Queenston Shale.

Fig. 4. Schematic - Robbins Open Gripper TBM

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Horizontal alignment is predominantly constrained by a combination of the existing tunnel right-of-way (for existing diversion Tunnels I and 2), the Niagara River, orientation of the tunnel intake to the existing TNCW tructure and minimum radii curves to suit TBM tunnelling. In plan. at the north end from Sta 0+000 to St. I +426 the alignment parallels the existing OPG power canal on OPG property. At Sta 1+426 the alignment curves southward and converges beneath the existing divcrsion tunnels following an existing easement along Stanley A venue beneath the downtown core of the City of Niagara Falls. From Sta 7+950 the alignment curves eastward on an azimuth perpendicular to the existing INeW structure within an easement beneath Niagara Parks Commission property. The final design alignment uses minimum horizontal curve radii of 1000 m to facilitate muck transportation by conveyor belt.

5.2. TUlJnel Construction Sequence The Diversion Tunnel will be excavated by an open gripper TBM of 14.44 m diameter with bored tunnelling progressing from the Outlet end to the Intake in the Niagara River. Concurrent with bored tunnelling, a "grout tunnel" will be excavated by drill and blast technique from the Intake. This will enable grouting of the highly penneable rock fonnations adjacent to the river near the Intakc, to be carried out before arrival of the TBM .

Initial lining rock support, to suit encountered rock conditions, will be insta lled from the TBM and trailing gear. Excavated muck will be transported from the TBM to the surface disposal area by muck conveyor.

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In order to meet the construction schedule the invert portion of the -:.ast-in-place final lining will be constructed concurrent with bored tunneling. This will be carried oul some distance back fromlhe TBM trai ling gear and will include cleaning of the invert, diversion of water secpage, installation and te ling of the waterproofing membrane system, installation of invert formwork and placing of concrete. For this purpose, a moving bridge will be installed allowing transportation to and from the TBM to cross this work area.

Once bored tunnelling is completed, construction of the top section of final lining will be carried out using 4 x 12 III long fomls . The sequence of membrane installation and concrete placement essentially follows the same pattern as the invert concrete production. Aftcr the final lining is installed. contact and interface grouting wi II be

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done as final activities prior to flooding of the tunnel and flow testing. Further details of the initial and final lining operations are provided below.

5.3. Tllnnel Lining The tunnel lining will be eonslructed by means of a two pass tunnel lining system that comprises the following components:

An initial lining that includes a combination of steel wire mesh, steel ribs, rock bolts and shOlcrete.

A final cast-in-place unreinforced concrete lining with a waterproofing membrane system to ensure that both water seepage from the tunnel and diffusion of chloride ions from the rock to prevent time dependent rock defonnation (swelling) does not occur.

Contact grouting carried out along the top of the final concrete lining after completion of concreting

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to close all voids in the crown and to provide a tight interface between rock mass, initial lining and final lining.

Finally, a high pressure interface grouting system is installed to pre-stress the final concrete lining and surrounding rock such the entire lining system remains in compression over the design life of the tunnel thereby eliminating the need for reinforcing steel.

5.4. Initial Lining The TBM and trailing gear arrangement allows for installation of rock support at two locations namely Location I and Location2. Ll is between 4 to 7 m back from the excavation face and L2 between 20 to 40 m back. Due to proximity to sensitive TBM electronic and mechanical components and limitations to TBM advance, installation of rock support in general and shotcrete, in particular, at Ll is limited to the minimum required for personnel safety. In the interests of tunnel advancement, the preference is for installation of the majority of rock support at L2. The assessment of installation of initial lining rock support at locations Ll and L2 takes into consideration the requirements for personnel safety and the rate of tunnel advancement. Depending on encountered rock conditions, this will result in progressive installation of rock support at Ll and L2 with full support being completed 40 m behind the excavation face.

Six rock conditions have been baselined in the OBR for which rock support types have been designed as follows:

i Support for Rock Condition 1 «0.2% of Tunnel) Applied in stable rock conditions with a uniaxial compressive strength comparable to lean concrete. A 50 mm thick sealing layer of shotcrete reinforced with mesh applied from L2 if roek is sensitive to water or will degrade when exposed to air.

ii Supportfor Rock Condition 2 «3% of Tunnel) Applied in Ll to provide safety for personnel working at the front of the TBM where blocks of ground are differentiable in otherwise stable rock conditions. It consists of steel ribs (C 100 x II steel channels) bolted with a limited number of 2.4 m long rock bolts to the tunnel crown and steel wire mesh fixed with the bolts. At L2, 70 mm of shotcrete is applied and additional rock bolts are installed. If necessary in ground sensitive to water, sealing shotcrete is applied to the invert section similar to Support Type I.

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iii Support for Rock Condition 3 (approximately 11 % o.fTunnel) Applied in L1 in friable ground, where small blocks of ground tend to fall from the tunnel crown if left unsupported. It consists of steel C150XI6 channels installed at 1.2 m intervals, 4.0m long rock bolts and steel wire mesh. Every second steel channel is extended to springline. At L2, 100 mm of shotcrete and more rock bolts are installed to support the full circumference of the tunnel.

iv Support for Rock Type 4 (approximately 29% of Tunnel) Applied at Ll where the tunnel crown and primary bedding planes are close to intersecting and an increasing number and size of unstable blocks are expected. Consisting of steel C150XI6 channels at 0.9 m intervals in the crown and 1.8 m intervals to the sidewalls (installed full round in the Queenston Formation as Type 4Q), 4.0-m long rock bolts and steel wire mesh in the tunnel crown. At L2, 130mm of shotcrcte and additional rock bolts are installed to complete full support of the tunnel.

v Support for Rock Type 5 (appoximately 47% of Tunnel) Applied in Ll in squeezing ground, where slabbing and spalling is experienced soon after excavation. It consists of steel ribs in form of mid weight W150X37 steel beams around the full circumference of the cross section at 1.8 rn intervals. As for support, Types 3 and 4 steel wire mesh and 6 m long rock bolts are installed in the tunnel crown to provide safety of the personal working at the front of the TBM. At L2, 160 mm of shotcrete is applied.

vi Support for Rock Type 6 (approximately 10% of Tunnel) Applied in L1 in exceptional ground conditions, where spalling and slabbing is experienced even in front of the excavation face. Heavy W200X59 steel beams, 6-m long rock bolts and 100 mm of shotcrete reinforced with steel wire mesh. An additional 160 mm of shotcrete and one additional layer of mesh reinforcement is installed at L2.

5.5. Final Lining The final lining consists of cast in place unreinforced concrete with a waterproofing membrane between the initial and final lining and both contact and interface grouting after concreting.

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I'l8 Mil .. • • " • • • • • • • • • • .. .. .. • .. .. .. .. .. .. .. .. • • • • • .. .. .. " • .. .. • • • •

(i) Waterproofing Membrane System The waterproofing membrane is designed to act as an impermeable layer between the initial and final lining preventing seepage of fresh water and diffusion of chloride ions to and from the surrounding rock that is susceptible to swelling thereby ensuring that time dependent deformation of the rock does not occur. The waterproofing membrane system consists of regulating shotcrete, where necessary, to smooth corners and edges and I

prevent damage of the waterproofing membrane during placement, membrane-backed geotextiIe fleece to protect the waterproofing membrane against the shotcrete, a double layer waterproofing membrane of 2 mm and 1.5 mm thickness respectively consisting of a Poly-Olefine (or polyethylene) product, produced in 2 m wide strips and heat welded together by double seams.

Rigorous and comprehensive quality assurance and quality control testing is required to ensure that the selected waterproofing membrane material and installation provides a final lining system that is 100% waterproof and diffusion resistant and includes: • laboratory testing to demonstrate chloride

diffusion barrier characteristics • in-situ pressure testing of each double weld seem • 100% in-situ vacuum testing of each panel of the

double layer membrane system, where the inner layer is manufactured with dimples to allow vacuum testing between the two membrane layers .

(ii) Final Lining Construction The sequence of final lining installation includes initial placement of invert concrete (and invert waterproofing membrane), concurrent with TBM tunneling, followed by placement of the remainder of the concrete lining system after completion of tunnelling. The invert will be cast in 12 m or 24 m long bays. A bridge across the invert concreting operation will facilitate transportation and material supply to the TBM while placement of the invert concrete system is in progress. Final lining of the tunnel section above the invert will commence once the tunnel is excavated. Before the final lining system is installed above .the invert, the preset rings for interface grouting and the waterproofing membrane system will be fixed to the tunnel walls and crown. Twelve metre long, adjustable diameter, steel forms, placed on the previously installed invert concrete, will be used for concreting the top section of the tunnel. Steel forms will be used to provide the smooth concrete finish required to limit friction losses to the flow of water in the tunnel. The

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adjustable diameter formwork allows adjustment of the diameter up to 260 mm to accommodate the variable thickness initial lining and provide a 600 to 700 mm thick final lining.

5.6. Contact Grouting After placement of final lining concrete, cement grout contact grouting of voids in the crown between the initial and final lining will be. carried out via grouting pipes attached at regular intervals to the intrados of the waterproofing membrane and extending through the final lining.

5.7. Interface Grouting Interface grouting of the final lining is required to create a continuous pre-stressed compression concrete support ring able to sustain internal water pressure without requiring steel reinforcement thereby eliminating the risk of corrosion of structural reinforcement within the 90 years design life. Grout, at specific pre-determined pressure (up to 30 bar), will be injected through a system of grout-hose rings installed between the initial lining and the waterproofing membrane system at 3 m centres. The grout-hose rings have pressure valves at 3 m circumferential centres that open under pressures releasing grout into the joint between initial lining and the "geotextile fleece" backing of the waterproofing system. The ends of the grout hoses penetrate through the waterproofing membrane system and the cast-in-place final lining into the tunnel. Grout blocking rings will be installed every 12 m to control the longitudinal flow of grout.

Interface grouting pressure for each individual section of tunnel are calculated taking the following considerations into account: • required long term pre-stressing pressure and

associated tunnel convergence • anticipated short term pre-stressing pressure and

associated tunnel convergence including deformation allowance for shrinkage of concrete and temperature contraction after watering up

• acceptable differential deformations including the shrinkage of concrete before watering up.

Interface grouting will be controlled by precise in-situ measurement of lining deformation during and after interface grouting. Pumping pressures as defined by structural analysis, will thereby be controlled within allowable limits. Regrouting will be required if the tunnel deformations (convergence of tunnel lining) are less than the values anticipated before watering up (Le., differential deformation associated with the conservation of the minimum

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long teml pre-stressing pressure including temperature contraction after watering up).

Interface grouting will be carried out in two phases with initial grouling through every second grout hose and re-h'fouting, if required, through intermediate unused hoses.

6 PROJECT UPDATE

As of June 2006, approximately nine months into the project, Phase 2 de ign and construction work is on schedule. At the Outlet, excavation of the Outlet canal is complete (except for the rock plug); dclivery of the TBM major components is approximately 50% complete and TBM assembly has commenced. Most of the tunneling support equipment has been delivered, including trailing gear, ventilat ion equipment, gantry crane, conveyor

equipment and transfonmers. A new 13.8-kY overhead power line and a 200-111m diameter water supply line have also been constructed.

At the Intake, marine-based work has commenced on the installation of the new ice acceleration wall , demolition of the existing acceleration wall. drill and blast excavation of the Intake approach channel and preparation for installation of sheet pile cofferdam cells.

7 ACKNOWLEDGMENTS

The authors would li ke to thank Ontario Power Generation (OPG) for their penmission to publish this paper.

Fig. 6. Outlet Site - June 2006

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