introduction to civil engineering - emucivil.emu.edu.tr/courses/insa100/geotechnical...

Introduction to Civil

Engineering

Geotechnical Engineering

by

Eriş Uygar

01 June 2015, EMU, Famagusta

• Studied Civil Engineering in the Eastern Mediterranean University, Mağusa, specialised in the field of Geotechnical Engineering after recieving MSc and PhD in the same university;

• Worked in an international and multidisciplinary engineering consultancy firm in the UK from 2005 to 2014, across various sectors of the business including: buildings and infrastructure, oil and gas and metros and civils.

• Experience and research interests include; soil-structure interaction modelling, soil insitu testing and monitoring of ground and structure displacements, potential damage assessment for buildings and tunnels.


Who am I ?


Contents

• First things first: what is Geotechnical Engineering ?

• Project 1: Mirdiff City Centre Mall, Dubai, UAE

• Project 2: Asia Petroleum Hub, Tanjung Bin, Malaysia

• Project 3: Crossrail 1, Contract C138, Moorgate and

Liverpool Street.

Do you think you can bear with me for a 1 hour long

presentation ?



This is a cliche but let’s ask

the key question once

again;

Is there any CIVIL

ENGINEERING structure

which doesn’t rest on soil

and rock or doesn’t interact

with soil and rock ?

All CIVIL ENGINEERING structures require consideration of principles of

GEOTECHNICAL ENGINEERING and SOIL & ROCK MECHANICS.

Geotechnical Investigation Investigation of Ground and Groundwater conditions,

Geological and Hydrological Setting and Environmental Considerations.

So, have you watched the movie called AVATAR ?

Floating forests, the Land of Pandora


Probably we

don’t need to

worry about soil

mechanics here

Zhangjiajie National Forest Park, China, planet Earth


These massive cliffs are created by

mother nature, (oops, or from the eye

of a Geotechnical engineer);

-by weathering and erosion of

rocks particularly due to wet

climate and thermal changes

all year round leading to

freeze-thaw of moisture in

rock causing cracks and

fracture of rock, a typical

example for -

Physical/Mechanical

Weathering.




Ground Investigation

Foundation Design

Ground Stabilisation

Tunneling and Deep

Excavation Design

Slope Stability and

Retaining Wall Design

Earthworks, Reinforced Earth and Landfill Design

Geotechnical Earthquake Engineering

not an exhaustive list !

Deals with Soil and Rock

Mechanics to provide the

following;


Geotechnical Engineering – Ground Investigation

• Site Walkover Survey and Report.

• Desk Study Report, including study of;

• historical maps, hydrological and geological setting, old mining

maps and reports, aquifer classification, flood risk assessment,

ecological surveys, records of past contaminating events, historical

exploratory hole records, ground stability hazard maps, ground gas

risk assessment.

• Design of Ground Investigation and Ground Investigation Report;

Factual Report by Ground Investigation Contractor and Ground

Investigation Report by Geotechnical Engineer.


Geotechnical Engineering – Ground Investigation – Site Walkover Survey

• Usually carried out at Feasibility Stage for Visual Assessment of;

• topography and superficial ground & groundwater conditions,

• Access arrangements for ground investigation equipment,

• Land use and permissions for investigation works,

• Sketches and photos of any visually identifieable features, hazards and risks.

Geotechnical Engineering – Ground Investigation – Site Walkover Survey


Black Country UTC Building Development

Geotechnical Engineering – Ground Investigation – Desk Study Sketch


Black Country UTC Building Development



• Simplest form of investigation carried out by studying any existing excavations in the

area and historical exploratory hole logs,

• Exploratory holes for sampling can be in the form of; • Trial pits, boreholes (cable percussion, which is an old skool way of drilling holes in the

ground or by dynamic sampling)

A trial pit Cable percussion rig Comacchio rig

Dynamic

sampling +

rock coring



• Data recorded during drilling to classify the ground profile based on visual

observations and laboratory testing.



• Insitu tests may one or few of the following; • Standard Penetration Test (SPT), Vane Shear Test (VST), Static Cone Penetration Test

(CPT), Pressuremeter Test (PMT), Dilatometer Test (DT).

Source: http://www.fhwa.dot.gov/engineering/geotech/pubs/05037/images/f038.gif

http://www.fhwa.dot.gov/engineering/geotech/pubs/05037/images/f038.gif



A typical PiezoCone Data with interpretation on soil classification

Typical Pressuremeter Data and Analysis

for undrained shear strength and unload-

reload modulus, example taken from a

test in Bangkok Clay (Blue Line Tube

extension tender, 2010).

-100

100

300

500

700

900

1100

1300

-0,20 -0,10 0,00 0,10 0,20 0,30 0,40

Pre

ssure

(kP

a)

Strain

Pressure v Cavity Strain

Pressure v Volumetric/Shear Strain

Shear Stress v Shear Strain

2Cu + P0

0

200

400

600

800

1000

1200

1400

1600

1800

3,00 4,00 5,00 6,00 7,00 8,00 9,00

Pre

ssure

(kP

a)

r (cm)

Axis Shifted with Cavity Radius Correction Unloading fitted Guess for Iterations Manually Fitted

0

200

400

600

800

1000

1200

1400

1600

1800

2,68 3,68 4,68 5,68 6,68 7,68

Pre

ssure

(kP

a)

r (cm)

Raw Data

Guess for iterations


Geotechnical Engineering – Foundation Design


• Consider concepts on; • Shear Strength, compressibility Bearing Capacity, Settlement and Expansion.

Mohr-Coulomb Theory on Shear Failure of soil and rock

Source:

http://images.books24

x7.com/bookimages/i

d_23746/fig4-1.jpg

Source: http://www.aboutcivil.org/imajes/soil-shear-strength.jpg

Terzaghi’s theory of one dimensional

consolidation.

• Saturated soil mechanics,

effective stress in soil and

dissipation of excess pore

water pressure.

Geotechnical Engineering – Foundation Design


• Types of foundations; • Shallow foundations (pad, strip, mat), deep foundations or pile foundations (bored, driven)

Shallow foundation for a

bridge viaduct, Worksop

2014, UK.

Pile foundations used as a retaining

measure and holding down anchorage

for a deep excavation and basement

in London Clay, Notting Hill 2012, UK.

Geotechnical Engineering – Ground Stabilisation


• Some examples of ground stabilisation include; shallow soil mixing, deep soil mixing,

stone columns, preloading, grouting, consolidation by prefabricated drains or vacuum

consolidation, dynamic compaction etc.

Shallow soil mixing, usually with cement and lime. https://youtu.be/jfG-jERhJBs?t=245

https://youtu.be/jfG-jERhJBs?t=245





Deep soil mixing, usually using pumped

cementitious binder slurry. https://youtu.be/UAs76Et9XWM

https://youtu.be/UAs76Et9XWM



Stone Columns, FARRS, ECML 2014, Doncaster, UK. https://youtu.be/F_kI6vQ5_gE

https://youtu.be/F_kI6vQ5_gE



Stone Columns, FARRS, ECML 2014, Doncaster, UK. https://youtu.be/F_kI6vQ5_gE

Countours of long term settlement

due to embankment weight in

millimetres.

Assessment of slope of ground

movement trough along a section

through the ECML

https://youtu.be/F_kI6vQ5_gE



Preloading and reinforced earth, Morfa to Berwick Link Road,

Llanelli 2006, Wales.

Reinforced earth, colliery spoil for embankment fill of approximately 12m height, proximity to

railway lines on two sides, monitoring with magnet extensometers and inclinometers, staged

construction allowing for consolidation and shear strength increase in the underlying soft clay.

Project 1 – Mirdiff City Centre Mall


• Sensitive structures + tight project budgets = need for value engineering.

• Significant savings can be attained, e.g. if shallow foundations are used instead of

piled foundations.

• Prediction of foundation settlements often difficult; need for use of sophisticated

methods; lack of transparency/sometimes reliability when using computer software.

• Practicable hand calculations required to control risks.

• Project fact sheet,

• 283,000m2 gross floor area

(excluding car parks).

• 6,700 labour force, 23 tower cranes.

• Overall duration design and

construction 35 months from concept

masterplan approval.

• Developer Majid Al Futtaim Group.

• Archtitects RTKL.

• Actual costs = a lot !.



• Concept of Nonlinear Stiffness Degradation; how can this concept be adopted in hand

calculations ?

• Nonlinear stiffness degradation curves can be obtained using extensive data from;

• Cone penetration testing, Menard pressuremeter testing, Shear wave velocity

testing, Large diameter Plate load testing.



• By using some of the published methods; Mayne et al (1999), O’Brien and Sharp

(2001), Lehane and Fahey (2002) and Loughlin and Lehane (2010).

• Stiffness mobilisation in sand, Fahey and Carter (1993), Shear stress

mobilisation in sand, Duncan and Chang (1970), Failure criterion: Mohr Coulomb.

• A methodology developed for the project, with verification using full size pad test

data by Briaud & Gibbens (1997) and Briaud (2007).

• Methodology also allowing for stiffness increase with depth.

-10

-5

0

5

10

15

20

0 200 400 600 800

Emax (MPa)

Lev

el

(m D

MD

)

Zone - 1Zone - 2Zone - 3Zone - 4Groundwater Level

variation in level of top of

weathered/extremely weak

sandstone

General trend of Emax within

weathered/extremely weak

sandstone

0.01

0.1

1

0.0001 0.001 0.01 0.1 1 10

Axial Strain (%)

E/E

max

Shear w . v. & SPTPLT resultsPMT results

Eq [14] Fit, at sm':100 kPaEq [14] Fit, at sm':39.6 kPaEq [14] Fit, at sm':16.5 kPa

c':0

f':35˚

Emax:150MPa

Example paramter plots

with depth derived from

insitu test data.



Photos from site during construction.

Project 2 – Asia Petroleum Hub, land reclamation


Reclaimed land off south coast of Malaysia.



Typical section through the

reclaimed fill.

• Reclaimed island on 18m of compressible Marine Clay

• 3m settlement during construction and 500mm in the long term

• Two main challenges;

• Unknown history, time application of the reclamation fill;

• Creep of soft Marine Clay in the long term causing negative skin friction on pile

foundations and settlement.



• Conceptual illustration of the problem;



• Design strategy;

• Segmental, spun concrete, driven piles for settlement sensitive large diameter

Oil and Petrol tanks.

• Ground stabilisation with Prefabricated Vertical Drains (PVDs) to facilitate

settlement and help manage site levels in the long term.

Spun concrete piles. PVDs.



• Design strategy;

• Trial embankment, adaptation of observational method of design, ongoing

monitoring and verification testing, regularly updated predictions, value

engineering during construction.

24 April 2015, METU NCC, Kalkanlı


• Results from site trials, monitoring data

and settlement prediction;

• Design: 0.8m PVD spacing, triangular

grid, Preloading with of 6.5m fill, eq to

120kPa, waiting period of 5 months to

achieve OCR:1.2, target U: 70%.

• Trials achieved: OCR:~1.3 and U >

80%, hence design spacing relaxed

to 1.0m.

Results from site trials, monitoring data and settlement prediction;

Prediction of working pile capacity by:

Project specific CAPWAP versus static load test correlation

Site specific dynamic pile formula versus static load capacity correlation, using PDA monitoring results

Static load test analysis


• Crossrail 1 is the largest infrastructure project in Europe, with an estimated budget of 15 Billion Pounds.

• It involves construction of new and development of a total of 15 underground and overground train/tube stations.

• Involved in the contract C138 including; New Moorgate Station excavation design category 2 check, Moorgate sewer diversion design and settlement mitigation of historical sewers, and Liverpool Street Queen Victoria Tunnel Ground Movement Impact Assessment and Mitigation Designs.

• Also involved in assessment of ground movement impact assessment for the new Cable Tunnel and London Underground Structures (switchrooms, communication rooms and substation).

Project 3 – Crossrail 1

• Moorgate Shaft, approximately 40m wide and 42m deep access shaft .

• The shaft will provide ventilation and emergency access to the new ticket hall.


https://youtu.be/HnE8_X5RjZg

• Very congested site in Central London, historical/listed buildings and new sky scrapers with glass façade around the shaft.

https://youtu.be/HnE8_X5RjZg

• Support design for the excavation and the ground movement effects to the surrounding structures are key drivers for the design.


• Staged construction design using finite element modelling, employing soil constitutive models.

• London Clay modelled considering degree of weathering with depth.

• Key checks involved estimations of mobilised lateral ground pressure at the face of the retaining structures and resulting support forces developed. Modelling considered staged construction and a coupled analysis is carried out to account for the drainage characteristics of the ground.

• Limit State approach is used following EN 1997 Eurocode 7 – Geotechnical Design.


Ultimate Limit State Serviceability Limit State EC7-DA1-C1

Partial Factors All factors 1.0 except for favourable

actions, which is to be 0.0 EC7-DA1-C2

Ground Parameters

Moderately conservative Shear Strength Moderately conservative

Worst Credible

Lower and upper limits considering a typical strain range between 0.05% to 0.1%

Stiffness Lower and upper limits considering a

typical strain range between 0.05% to 0.1%

Elastic perfectly plastic, Mohr-Coulomb Material Models

Elastic perfectly plastic, Mohr-Coulomb

Ground Behaviour

Strata Active side Passive side Strata Active side* Passive side

LC1 D UD/S LC1 UD/S UD/S LC2 D UD/S LC2 UD/S UD/S LG1 D UD/S LG1 UD/S UD/S LG2 D UD/S LG2* D UD/S

LG3 D D LG3 D D LG4 D D LG4 D D

Notes: EC7-DA1-C1: Eurocode 7 design approach 1 combination 1 EC7-DA1-C2: Eurocode 7 design approach 1 combination 2 LC1: London Clay A3/B, LC2: London Clay A2 LG1: Lambeth group upper mottled beds, LG2: Lambeth group interbedded layers, LG3: Lambeth group sand channels LG4: Lambeth group Upnor formation D: drained, UD: undrained, S: softened

• Remarks and closure;

• Geotechnical Engineering is often called as “Black Art”, as there are many unknowns involved in a geotechnical design.

• Ground conditions rarely reflect homogeneous and isotropic conditions and yet most of the geotechnical concepts can’t deal with anything more sophisticated than these conditions.

• Unlike calculated and well know nature of any other building material, soil and rock always vary unpredictably and hence a risk based approach should always be adopted in a geotechnical design. Predictions carried out on soil behaviour should consider a range of variation.

• Geotechnical input to projects is essential and can provide significant cost savings.

• Geotechnical Engineering should be regarded as an essential integral part of any civil engineering project especially in areas where ground conditions are poor and seismicity is a concern.

Are you up for the challenge then ?

Don’t be afraid to become a Geotechnical Eng.

introduction to civil engineering - emucivil.emu.edu.tr/courses/insa100/geotechnical...

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