Use of Numerical Modelling to Mitigate Ground Risk CECA MEETING – SEPT 2017 Gavin & Doherty Geosolutions Ltd.
Overview Todays Presentation…. o Introduction to GDG o Finite Element Modelling & Calibration o Case Studies o Flood Defences o Retaining Walls o High rise foundations o Risk Analysis o Conclusions
GDG Introduction About us …. o Gavin & Doherty Geosolutions (GDG) is a specialist geotechnical & civil engineering consultancy o Offices in London, Edinburgh, Dublin, and Belfast, o GDG was formed in 2011 in a challenging market o Grown throughout the last five years o Team of 40 highly talented engineers o Majority of our staff are PhD qualified o We provide innovative geotechnical solutions & efficient civil engineering designs for challenging projects
Engineering Design Services Structures Infrastructure R&D Offshore Renewables
Engineering Design Services o Concept Design o Site Investigation Scoping o Site Investigation Interpretation o Civil Engineering Design o Temporary Works Design o Numerical Modelling (FEA) o Performance monitoring / instrumentation analysis o Expert Witness Services
INFRASTRUCTURE
INFRASTRUCTURE SERVICES & EXPERTISE o Geotechnical Interpretation & Ground Modelling for Road, Railway and Flood Defence Schemes o Geological Assessments & Mapping o Earthworks Design o Material Suitability o Hydrogeological review o Civil Engineering Design o Numerical Modelling o Soil-Structure-Water Interaction Analysis o Back-analysis of failures & Root Cause Analysis
URBAN STRUCTURES
URBAN STRUCTURES SERVICES & EXPERTISE o Basement & Foundation Engineering o Soil-Structure Interaction o Ground Movement Assessments o Retaining Wall Analysis o Excavation Support and Propping Design o Construction Sequencing & Temporary Works o Pile Design & Piled Raft Analysis o Tunnel and basement impact assessments o Ground Improvement Engineering
OFFSHORE & MARINE
OFFSHORE & MARINE SERVICES & EXPERTISE o Analysis and Design of Ports & Harbours o Quay Wall Numerical Modelling o Offshore Substructure Analysis o Offshore wind foundation engineering o Gravity structures, monopiles, jacket piles, etc … o Pile Installation analysis & Interpretation of offshore driving data o Site suitability assessments o Jack-up vessel studies o Back-analysis of failures & Root Cause Analysis
RELEVANT PROJECTS RENEWABLES • 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
RENEWABLES SERVICES & EXPERTISE o Site suitability and feasibility studies for onshore wind and onshore solar farms o Geotechnical risk studies o Peat stability assessments o Earthworks engineering for roads, crane bases, hardstands, etc. o Foundation design for gravity and piled bases o Interaction analysis for soil-structure-turbine behaviour.
Ground Risk • What is Ground Risk ? Technical Presentation www.gdgeo.com Sept 2017
Design Tools Available • Analytical – Traditional Theoretical Hand (spreadsheet) Calculations • Empirical – Traditional Approaches based on experience of 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) Technical Presentation www.gdgeo.com Sept 2017
Finite Element Method • 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 Technical Presentation www.gdgeo.com Sept 2017
Basics of Geotechnics • Soil is highly non-linear – Pick an appropriate constitutive model Elastic-Plastic Stress Real Soil Strain Technical Presentation www.gdgeo.com Sept 2017
Finite Element Method • FEM CALIBRATION – Simulation of Lab Testing – Look for repeatability – Use range of test types Technical Presentation www.gdgeo.com Sept 2017
Finite Element Method • FEM CALIBRATION – Simulation of Field Testing Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS • Access Shaft for TBM • Complex Ground Conditions • Underlying Aquifer • Base Heave a Serious Concern ! • Design Solution Needed Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • Model Calibration Non-Plastic Till Fine Sand to Silt Plastic Till Sand to Sand and Gravel 𝑬𝒔𝒃𝒋𝒐𝒃𝒉𝒇 𝑼𝒛𝒒𝒇 - Drained Drained Undrained Drained 𝑸𝒇𝒔𝒏𝒇𝒃𝒄𝒋𝒎𝒋𝒖𝒛 1 × 10 −6 4 × 10 −5 8 × 10 −8 3 × 10 −4 𝑛 𝑡 18 18 24 18 𝜹 𝒗𝒐𝒕𝒃𝒖 𝑙𝑂 𝑛 3 𝜹 𝒕𝒃𝒖 20 20 24.3 20 𝑙𝑂 𝑛 3 - 0.5 0.5 0.301 0.5 𝒇 𝟏 𝒔𝒇𝒈 𝑁𝑄𝑏 30 30 20 30 𝑭 𝟔𝟏 𝒔𝒇𝒈 𝑁𝑄𝑏 30 30 20 30 𝑭 𝒑𝒇𝒆 𝒔𝒇𝒈 𝑁𝑄𝑏 90 90 80 90 𝑭 𝒗𝒔 𝑸𝒑𝒙𝒇𝒔 (𝒏) - 0.5 0.5 0.5 0.5 𝑙𝑄𝑏 0 0 0 0 𝒅 𝒔𝒇𝒈 𝝌 ° 35 35 35.9 35 𝝎 ° 5 5 9 5 𝒒 𝒔𝒇𝒈 𝑙𝑄𝑏 100 100 100 100 - 0.9 0.9 0.9 0.9 𝑺 𝒈 - 1 0.8 1.2 0.8 𝒍 𝟏,𝒚 Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS • Undrained versus Drained Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS • Pore Pressures (a) End of Excavation (b) 10 weeks (c) 20 weeks (d) 50 weeks (a) (b) Technical Presentation (c) (d) www.gdgeo.com Sept 2017
CASE STUDY 1 • TORONTO SEWER NETWORK TUNNEL ACCESS SHAFTS • Failure Avoided • Facilitated Economic Construction Sequence • Observational Method Used to Minimise Risk Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 2 • NATIONAL GALLERY UNDERPINNING ANALYSIS 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 www.gdgeo.com Sept 2017
CASE STUDY 2 • NATIONAL GALLERY UNDERPINNING ANALYSIS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 2 • NATIONAL GALLERY UNDERPINNING ANALYSIS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 2 • NATIONAL GALLERY UNDERPINNING ANALYSIS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 2 • NATIONAL GALLERY UNDERPINNING ANALYSIS Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 2 • 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. Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 3 • Flood Defences Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 3 • Flood Wall Analysis • Stability Modelling • Seepage Analysis Deemed Critical Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 3 • Flood Defence Design Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 3 • Flood Risk Analysis Technical Presentation www.gdgeo.com Sept 2017
CASE STUDY 3 • Flood Risk Analysis 5.5 4.5 Design Flood Level 3.5 2.5 1.5 4 1.2 . 0.5 1 Gravel -0.5 Elevation (m) -1.5 -2.5 1 2.6 2.2 2 . 4 0.8 1.8 2 1.6 0.6 -3.5 Peat -4.5 0.2 -5.5 0.4 0.12612 m³/days 0 -6.5 Silt 2.8537 m³/days . 6 8 -7.5 2 0 2 -8.5 m ³ / -9.5 d a y -10.5 Gravel s -11.5 -12.5 -13.5 0 5 10 15 20 25 30 35 Distance (m) Technical Presentation www.gdgeo.com Sept 2017
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