Use of Numerical Modelling to Mitigate Ground Risk CECA MEETING - - PowerPoint PPT Presentation

Use of Numerical Modelling to Mitigate Ground Risk

Gavin & Doherty Geosolutions Ltd.

CECA MEETING – SEPT 2017

Overview

• Introduction to GDG
• Finite Element Modelling & Calibration
• Case Studies
• Flood Defences
• Retaining Walls
• High rise foundations
• Risk Analysis
• Conclusions

Todays Presentation….

GDG Introduction

• Gavin & Doherty Geosolutions (GDG) is a specialist

geotechnical & civil engineering consultancy

• Offices in London, Edinburgh, Dublin, and Belfast,
• GDG was formed in 2011 in a challenging market
• Grown throughout the last five years
• Team of 40 highly talented engineers
• Majority of our staff are PhD qualified
• We provide innovative geotechnical solutions & efficient

civil engineering designs for challenging projects About us ….

Engineering Design Services

Structures Infrastructure Offshore Renewables R&D

Engineering Design Services

• Concept Design
• Site Investigation Scoping
• Site Investigation

Interpretation

• Civil Engineering Design
• Temporary Works Design
• Numerical Modelling (FEA)
• Performance monitoring /

instrumentation analysis

• Expert Witness Services

INFRASTRUCTURE

INFRASTRUCTURE

• Geotechnical Interpretation & Ground

Modelling for Road, Railway and Flood Defence Schemes

• Geological Assessments & Mapping
• Earthworks Design
• Material Suitability
• Hydrogeological review
• Civil Engineering Design
• Numerical Modelling
• Soil-Structure-Water Interaction Analysis
• Back-analysis of failures & Root Cause Analysis

SERVICES & EXPERTISE

URBAN STRUCTURES

URBAN STRUCTURES

SERVICES & EXPERTISE

• Basement & Foundation Engineering
• Soil-Structure Interaction
• Ground Movement Assessments
• Retaining Wall Analysis
• Excavation Support and Propping Design
• Construction Sequencing & Temporary Works
• Pile Design & Piled Raft Analysis
• Tunnel and basement impact assessments
• Ground Improvement Engineering

OFFSHORE & MARINE

OFFSHORE & MARINE

SERVICES & EXPERTISE

• Analysis and Design of Ports & Harbours
• Quay Wall Numerical Modelling
• Offshore Substructure Analysis
• Offshore wind foundation engineering
• Gravity structures, monopiles, jacket piles, etc…
• Pile Installation analysis & Interpretation of
• ffshore driving data
• Site suitability assessments
• Jack-up vessel studies
• Back-analysis of failures & Root Cause Analysis

• NNG Wind Farm
• Rampion Wind Farm
• Zawtika Gas Jacket Pile Analysis
• Hornsea Met Mast
• Firth of Forth Wind Farm Forensics
• Dogger Bank Jackup Analysis
• Shell Conductor Installation Studies North Sea
• Horizont Jacket Pile FEED

RELEVANT PROJECTS RENEWABLES

RENEWABLES

SERVICES & EXPERTISE

• Site suitability and feasibility studies for
• nshore wind and onshore solar farms
• Geotechnical risk studies
• Peat stability assessments
• Earthworks engineering for roads, crane bases,

hardstands, etc.

• Foundation design for gravity and piled bases
• Interaction analysis for soil-structure-turbine

behaviour.

Technical Presentation Sept 2017 www.gdgeo.com

• What is Ground Risk ?

Ground Risk

Technical Presentation Sept 2017 www.gdgeo.com

• Analytical – Traditional Theoretical Hand (spreadsheet)

Calculations

• Empirical – Traditional Approaches based on experience
• f empirical evidence
• Numerical – Finite Element (or Finite Difference)
• Observational Design Approaches

Pick the most appropriate tool for your project (consider the limitations of the tool, the complexity of the project and the accuracy required)

Design Tools Available

Technical Presentation Sept 2017 www.gdgeo.com

• Numerical Modelling Procedure to Determine Soil-

Structure Response

• Modern Software Capable of Considering Complex

Geometries

• The geometry is discretised into a mesh and the stresses

and strains are resolved as loads/actions are applied

• Can accurately determine ground movements and

structural stresses, provided the model is well calibrated

• Calibration requires (a) DATA and (b) EXPERTISE

Finite Element Method

Technical Presentation Sept 2017 www.gdgeo.com

• Soil is highly non-linear

– Pick an appropriate constitutive model

Basics of Geotechnics

Stress Strain Real Soil Elastic-Plastic

Technical Presentation Sept 2017 www.gdgeo.com

• FEM CALIBRATION

– Simulation of Lab Testing – Look for repeatability – Use range of test types

Finite Element Method

Technical Presentation Sept 2017 www.gdgeo.com

• FEM CALIBRATION

– Simulation of Field Testing

Finite Element Method

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS
• Access Shaft for TBM
• Complex Ground Conditions
• Underlying Aquifer
• Base Heave a Serious Concern !
• Design Solution Needed

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• Model Calibration

CASE STUDY 1

Non-Plastic Till Fine Sand to Silt Plastic Till Sand to Sand and Gravel 𝑬𝒔𝒃𝒋𝒐𝒃𝒉𝒇 𝑼𝒛𝒒𝒇

• Drained

Drained Undrained Drained 𝑸𝒇𝒔𝒏𝒇𝒃𝒄𝒋𝒎𝒋𝒖𝒛 𝑛 𝑡 1 × 10−6 4 × 10−5 8 × 10−8 3 × 10−4 𝜹𝒗𝒐𝒕𝒃𝒖 𝑙𝑂 𝑛3 18 18 24 18 𝜹𝒕𝒃𝒖 𝑙𝑂 𝑛3 20 20 24.3 20 𝒇𝟏

• 0.5

0.5 0.301 0.5 𝑭𝟔𝟏

𝒔𝒇𝒈

𝑁𝑄𝑏 30 30 20 30 𝑭𝒑𝒇𝒆

𝒔𝒇𝒈

𝑁𝑄𝑏 30 30 20 30 𝑭𝒗𝒔

𝒔𝒇𝒈

𝑁𝑄𝑏 90 90 80 90 𝑸𝒑𝒙𝒇𝒔 (𝒏)

• 0.5

0.5 0.5 0.5 𝒅𝒔𝒇𝒈 𝑙𝑄𝑏 𝝌 ° 35 35 35.9 35 𝝎 ° 5 5 9 5 𝒒𝒔𝒇𝒈 𝑙𝑄𝑏 100 100 100 100 𝑺𝒈

• 0.9

0.9 0.9 0.9 𝒍𝟏,𝒚

• 1

0.8 1.2 0.8

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS
• Undrained versus Drained

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS
• Pore Pressures

(a) End of Excavation (b) 10 weeks (c) 20 weeks (d) 50 weeks

CASE STUDY 1

(a) (b) (c) (d)

Technical Presentation Sept 2017 www.gdgeo.com

• TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS
• Failure Avoided
• Facilitated Economic Construction Sequence
• Observational Method Used to Minimise Risk

CASE STUDY 1

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Facilitate basement extension

• Geotechnical interpretation
• Geophysical profiling
• 3D Settlement Analysis of

Construction Stages

• Recommendation about

underpinning construction

• Final settlement design for

temporary and permanent works.

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING ANALYSIS

CASE STUDY 2

Technical Presentation Sept 2017 www.gdgeo.com

• NATIONAL GALLERY UNDERPINNING
• Settlements predicted to be less than 10mm in worst

case

• Generally less than 5 mm
• Concrete underpinning shown to be appropriate,

however construction quality control critical

• Monitoring system tailored to target critical area of the

building and critical point in the construction timeline

• Constant monitoring compared to design predictions

with target levels set to stop construction if required.

CASE STUDY 2

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Defences

CASE STUDY 3

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Wall Analysis

CASE STUDY 3

• Stability Modelling
• Seepage Analysis

Deemed Critical

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Defence Design

CASE STUDY 3

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Risk Analysis

CASE STUDY 3

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Risk Analysis

CASE STUDY 3

0.2 0.4 0.6 0.8 1 1.2 1 . 4 1.6 1.8 2 2.2 2 . 4 2.6

Design Flood Level

Gravel Gravel Silt

Peat

. 6 8 2 2 m ³ / d a y s 2.8537 m³/days 0.12612 m³/days

Distance (m)

5 10 15 20 25 30 35

Elevation (m)

• 13.5
• 12.5
• 11.5
• 10.5
• 9.5
• 8.5
• 7.5
• 6.5
• 5.5
• 4.5
• 3.5
• 2.5
• 1.5
• 0.5

0.5 1.5 2.5 3.5 4.5 5.5

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Risk Analysis

CASE STUDY 3

0.2 0.4 0.6 0.8 1 1.2 1 . 4 1.6 1.8 2 2.2 2 . 4 2.6

Design Flood Level

Gravel Gravel Silt

Peat

. 6 8 2 2 m ³ / d a y s 2.8537 m³/days 0.12612 m³/days

Distance (m)

5 10 15 20 25 30 35

Elevation (m)

• 13.5
• 12.5
• 11.5
• 10.5
• 9.5
• 8.5
• 7.5
• 6.5
• 5.5
• 4.5
• 3.5
• 2.5
• 1.5
• 0.5

0.5 1.5 2.5 3.5 4.5 5.5 . 4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2 . 4 2.6 2.8

Gravel Gravel Silt

Peat

Distance (m)

5 10 15 20 25 30 35

Elevation (m)

• 13.5
• 12.5
• 11.5
• 10.5
• 9.5
• 8.5
• 7.5
• 6.5
• 5.5
• 4.5
• 3.5
• 2.5
• 1.5
• 0.5

0.5 1.5 2.5 3.5 4.5 5.5

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Risk Analysis

CASE STUDY 3

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Wall Analysis

CASE STUDY 3

• Conceptual hyrogeological model developed
• Model Developed for Current Condition
• Model Calibrated Against Dynamic Borehole Records

Current Ground Level

Distance (m)

5 10 15 20 25 30 35 40 45 50 55

Elevation (m)

• 9.55
• 8.55
• 7.55
• 6.55
• 5.55
• 4.55
• 3.55
• 2.55
• 1.55
• 0.55

0.45 1.45 2.45 3.45 4.45 5.45

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Wall Analysis

CASE STUDY 3

• Calibration Process
• Consider River Levels
• Tidal Variations

Technical Presentation Sept 2017 www.gdgeo.com

• Flood Wall Analysis

CASE STUDY 3

• Model Storm Events
• Consider River Levels
• Tidal Variations
• Design Options
• 1

1 2 3 4 5 6 12 18 24 30 36 Head (m) Time (hours)

The change in Head (m) over time (hours)

• 0.2

0.2 . 4 0.6 1

Low River Level -0.20 mOD Gravel Design Flood Level 3.80 mOD Gravel Silt Swale River Wall Flood Defence Wall Golf Course Road Hight Tide 1.54 mOD

0.32512 m³/days . 2 8 5 2 9 m ³ / d a y s

Distance (m)

5 10 15 20 25 30 35 40 45 50 55

Elevation (m)

• 9.55
• 8.55
• 7.55
• 6.55
• 5.55
• 4.55
• 3.55
• 2.55
• 1.55
• 0.55

0.45 1.45 2.45 3.45 4.45 5.45

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• 32 Storey High Rise Development
• Several Concentrated Column Loads

with very high forces

• High wind moment on tower
• Piled-Raft deemed most

appropriate solution

• Stratigraphy consisted of London

Clay

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• Non-linear soil model used
• Moment applied as an

eccentric force on a lever arm above the raft

• Pile Design optimised

iteratively

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• Designed to a settlement criteria rather than

to a capacity value

• S<35mm

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• Examine pile utilisation & optimise design
• Piles shortened by 7m

Technical Presentation Sept 2017 www.gdgeo.com

• Piled-Raft for High Rise Development

CASE STUDY 4

• Analyse the impact of

the new raft on existing contiguous wall along site boundary

• Contig wall predicted

to displace by approximately 9 mm

• Existing inclinometer

casings used as a cheap/efficient monitoring solution

Technical Presentation Sept 2017 www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS
• Redevelopment of Harbour, involving residential & office buildings on

piled pier

• Focus on estimating settlement of pipe piles

CASE STUDY 5

Technical Presentation Sept 2017 www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS

CASE STUDY 5

Technical Presentation Sept 2017 www.gdgeo.com

• MARINA PILE SETTLEMENT ANALYSIS

CASE STUDY 5

• Using state of the art

settlement models to assess foundation performance (in-house design tools)

• Excellent prediction
• Confirmed pile

acceptability

Technical Presentation Sept 2017 www.gdgeo.com

• Risk Modelling on a Large Scale (Rail Network)

CASE STUDY 6

2,800Km Track 4,900 Earthworks 5,100 Bridges 900 Level Crossings

Technical Presentation Sept 2017 www.gdgeo.com

Portarlington Derailment Aug 2008 Manulla Junction Landslide Aug 2007 Wicklow Derailment Nov 2009 Rushbrooke Rock Falls March 2014

• Recent Failures

CASE STUDY 6

Technical Presentation Sept 2017 www.gdgeo.com

Waterford Rockfall Dec 2013 Kilkenny Waterford Line Landslip Dec 2013 Tullamore Soil Slips and Rock Falls 2011/2012 Cabra Slope Failures 2012

CASE STUDY 6

Technical Presentation Sept 2017 www.gdgeo.com

PROBABILISTIC MODELLING

• High Level of Uncertainty Across the

Asset Characteristics

• Consider COV of input parameters

depending on data source

• Develop quantifiable risk profiles
• Hasofer Lind method used to

calculate the probability of failure associated with each asset and its coupled limit state

• Outputs: reliability index (β),

probability of failure

CASE STUDY 6

g(X) = R-S Pf probability

• f failure

ßs[g(x)] E[g(x)] E[g(x)]

s[g(x)]

ß[g(x)] =

Outputs: reliability index (β), probability of failure

Technical Presentation Sept 2017 www.gdgeo.com

• Risk Modelling on a Large Scale (Rail Network)
• Possible to quantify ground risk
• 4000 Assets
• No excuses for individual sites!

CASE STUDY 6

Technical Presentation Sept 2017 www.gdgeo.com

• Karst Risk Analysis
• Importance of Desk study research

CASE STUDY 7

Technical Presentation Sept 2017 www.gdgeo.com

CASE STUDY 7

Soil Profile from Intrusive Investigation Layer No. Depth below ground level (bgl) Soil Type Description 1 0.6 to 0.9 m Made Ground Grey sandy GRAVEL with cobbles 2 0.9 m to 4 m* Dynamic Probe No. T2 encountered soft soil to 11.1 m bgl. Glacial Till The till comprises reddish brown sandy gravelly, low plasticity CLAY. The fines content of the soil was between 35 and 50%. 3 Below 4 m Waulsortian Limestone Light Grey, massive reef

• LIMESTONE. The rock is strong to

very strong, with strong evidence

• f karst solution features

Technical Presentation Sept 2017 www.gdgeo.com

CASE STUDY 7

Soil Profile from Intrusive Investigation Layer No. Depth below ground level (bgl) Soil Type Description 1 0.6 to 0.9 m Made Ground Grey sandy GRAVEL with cobbles 2 0.9 m to 4 m* Dynamic Probe No. T2 encountered soft soil to 11.1 m bgl. Glacial Till The till comprises reddish brown sandy gravelly, low plasticity CLAY. The fines content of the soil was between 35 and 50%. 3 Below 4 m Waulsortian Limestone Light Grey, massive reef

• LIMESTONE. The rock is strong to

very strong, with strong evidence

• f karst solution features

Technical Presentation Sept 2017 www.gdgeo.com

CASE STUDY 7

• Geophysics used to map risk

Technical Presentation Sept 2017 www.gdgeo.com

CASE STUDY 7

• Pragmatic Construction Regime Proposed

Technical Presentation Sept 2017 www.gdgeo.com

SUMMARY

• Advanced design tools have a place in the right projects
• FEM can allow more efficient design, save money and decrease risk
• Calibration is critical
• Recommend numerical modelling coupled with observational

approach

• Monitoring provides the confidence to allow construction to proceed
• n time and in budget

Technical Presentation Sept 2017 www.gdgeo.com

• QUESTIONS ???

Contact: Paul Doherty pdoherty@gdgeo.com

Conclusions