Excavations and Foundations in Soft Soils – Hans-Georg Kempfert (TCE0003)

Excavations and Foundations in Soft Soils – Hans-Georg Kempfert, CONTENTS:

1        Introduction 

1.1     General

1.2     Safety regulations in geotechnical engineering

1.2.1   The ultimate and serviceability limit states

1.2.2   Total safety concept

1.2.3   Partial safety concept and the German Code

1.2.4   European code of standard

1.2.5   Comparison between Eurocode EC 7-1 and German Code DIN 1054

2        Material properties of soft soils   

2.1     General

2.2     Sampling

2.3     Basic index properties

2.4     Compression properties

2.4.1   General

2.4.2   One-dimensional compression

2.4.3   Two and three-dimensional compression

2.5     Strength properties

2.5.1   General

2.5.2   Total and effective stress analysis

2.5.3   Undrained strength

2.5.4   Drained strength

2.6     Deformation properties

2.6.1   General

2.6.2   Drained and undrained behaviour

2.6.3   Effect of depth on modulus of elasticity

2.6.4   Effect of anisotropy on modulus of elasticity

2.6.5   Constrained Modulus from one-dimensional compression

2.6.6   Unloading/reloading modulus of elasticity

3        Constitutive soil models and soil parameters   

3.1     Constitutive soil models

3.1.1   Introduction

3.1.2   Linear elastic stress-strain law

3.1.3   Non-linear elastic stress-strain law

3.1.4   Variable elastic stress-strain law

3.1.5   Elasto-plastic stress-strain law

3.1.6   Elasto-visco-plasticity

3.1.7   Hypoplasticity

3.1.8   Cap models

3.1.9   The constitutive soil models used in PLAXIS FE-program

3.1.10 Requirement for constitutive soil models – example excavation

3.1.10 Constitutive relations for interface elements

3.2     Derivation of soil parameters for numerical analysis

3.2.1   General

3.2.2   Determination of compression parameters

3.2.3   Determination of strength parameters

3.2.4   Deformation parameters under deviatoric loading condition

3.2.5   Contact behaviour between wall material and soft soil

3.3     Calibration of soil parameters

3.3.1   Drained test behaviour

3.3.2   Undrained test behaviour

4        Supported excavations in soft soil deposits      

4.1     General

4.2     Unsupported excavations

4.3     Excavation retaining systems in soft soils

4.3.1   Type of wall

4.3.2   Type of wall support

4.3.3   Recommendations for retaining structures according to EAB

4.4     Behaviour of excavations

4.4.1   General

4.4.2   Earth pressure, reaction and section forces

4.4.3   Movements in and around an excavation

4.4.4   Excavation stability in soft soils

4.5     Execution of excavations

4.6     Safety factor in design of retaining structures

4.7. Drained/undrained analysis of excavation

4.7.1   General

4.7.2   Is drained or undrained behaviour most critical for design of supported excavations?

4.7.3   The time limit for undrained and drained condition

4.7.4   Determination of the earth pressure in short term using the effective strength and the pore pressure parameters

4.7.5   Earth pressure in short term using the undrained strength

4.7.6   Comparison of the different approaches

4.8     Stress paths in excavations

4.9     Some reviews of FE-analysis of excavations

4.9.1   General

4.9.2   Factors affecting the performance of excavations

4.10    Parameter study

4.10.1 General

4.10.2 System geometry

4.10.3 Sensitivity study of the hardening soil model parameters

4.10.4 Effect of berms on deformation of excavations

4.10.5 Effect of the bottom support

4.10.6 Comparison of drained and undrained analysis

4.10.7 Mobilization of the passive resistance of a cohesive soil

4.11    German recommendation for excavation in soft soils

4.11.1 General

4.11.2 The shear strength and the coefficient of earth pressure at rest

4.11.3 Earth pressures and reactions

4.11.4 Water pressure

4.11.5 Embedment depth and section forces

4.11.6 Basal failure

4.11.7 Drainage measures in excavation

4.12    Case histories

4.12.1 General

4.12.2 Project-I: Damgasse – Constance

4.12.3 Project-II: Markgrafenstrasse – Constance

4.12.4 Project-III: Seeuferhaus – Constance

4.12.5 Project-IV: Seearkaden Starnberg

4.12.6 Project-V: Karstadt building in Rosenheim

5        Shallow foundations on soft soils

5.1     General

5.2     Historical foundation on soft soil deposits

5.3     Type of shallow foundations

5.4     Settlement calculations – the serviceability limit state

5.4.1   Soft soils deformation behaviour and calculation methods

5.4.2   Stresses and settlements due to external load

5.4.3   Time settlement behaviour, magnitude and components of settlements of shallow foundations

5.4.4   Allowable settlements, tilts and angular distortions

5.5     Case histories of buildings on raft foundations

5.5.1   General

5.5.2   Soil condition

5.5.3   Review of settlement observations

5.5.4   Summary of the back analyses results

5.5.5   Effect of load increment and rate on settlement prediction

5.6     Two case histories with excessive settlements

5.6.1   General

5.6.2   Case A: office building

5.6.3   Case B: Storage tanks

5.6.4   Numerical analysis

5.7     Case history of an embankment

5.8     Case history of settlement due to shrinkage

5.9     Safety of shallow foundations

5.10    Design of raft foundation

5.10.1 General

5.10.2 Parameter study

5.10.3 Numerical analysis using the FEM

5.10.4 Verification of the modified subgrade reaction method on selective projects

5.10.5 Effect of creep of the soil on flexural stress of a plate

5.11    Summary and recommendations

6        Pile foundation       

6.1     Introduction

6.2     Pile types and construction methods

6.2.1   Selection of appropriate pile type

6.2.2   Displacement piles

6.2.3   Bored piles

6.2.4   Micropiles

6.3     Pile bearing behaviour

6.4     Axial pile resistance

6.4.1   General

6.4.2   Pile resistance from static Load Tests

6.4.3   Dynamic pile testing

6.4.4   Pile resistance against horizontal loadings

6.4.5   Determination of pile resistance

6.4.6   Change of the bearing capacity of piles with time

6.5     Negative skin friction

6.5.1   General

6.5.2   Neutral point

6.5.3   Actions arising from negative skin friction

6.6     Lateral loads and settlement bending

6.8     Special pile foundations in deep soft soil deposits

6.9     Raft foundation on floating injection piles (RFIP)

6.10    Case histories on RFIP-foundation system

6.10.1 General

6.10.2 Project I (RFIP-foundation system)

6.10.3 Project II (RFIP)     ‘

6.10.4 Project III (Floating displacement piles)

6.10.5 Project IV (excavation and old building stabilisation with RFIP).

6.10.6 Summary

7        Soil stabilisation with column-like elements    

7.1     General

7.2     Reinforced embankments on pile-like elements

7.2.1   General

7.2.2   Load transfer mechanism

7.3     Stone columns and sand compaction piles

7.3.1   General

7.3.2   Principles of design and analysis

7.4     Geotextile encased sand/gravel columns (GEC)

7.4.1   General

7.4.2   Installation method

7.4.2   The bearing system of the GEC

7.4.3   The analytical calculation approach

7.5     CSV Method

7.5.1   General

7.5.2   The method of installation

7.5.3   The bearing system

7.5.4   Design and analysis

7.6     Deep mixing method (DMM)

7.6.1   Introduction

7.6.2   Dry deep mixing method

7.6.3   Wet deep mixing method

7.6.4   Jet pile method

7.7     Unreinforced pile like elements

7.7.1   Grouted stone/gravel column

7.7.2   Ready-mixed mortar columns

7.7.3   Unreinforced concrete columns

7.8     Displacement and bored piles

7.9     Case histories

7.9.1   Muehlenberger loch – geotextile-encased sand columns (GEC)…

7.9.2   Hamburg-Berlin railway line: reinforced embankment on pile like elements

7.9.3   City road Trasa Zielona in Lublin-Polen: wet deep soil mixing

7.9.4   A multistory building on wet deep mixing columns

7.9.5   Pad and strip foundations on wet deep mixing columns

7.9.6   Highway bridges supported on wet deep mixing columns

7.9.7   Restoration of an offshore retaining wall with CSV-columns

7.9.8   Stabilisation of 5-storey building foundation and underground parking with CSV-columns