How To Undertake Finite Element Based Geotechnical Analysis

Mar, A

First Published - November 2002
Softback, 58 Pages

The aim of this book is to guide both new and experienced analysts on the use of finite element techniques to solve geotechnical problems.

Finite element analysis has been used within the realm of geotechnical engineering for some time. Universities and various specialist organisations now have experts in this field. More recently, however, there have been significant increases in the availability and affordability of computer power, and a proliferation of finite element packages that are relatively easy to use thus drastically reducing the learning curve for a novice user. This combined with the increased pressure for ever more efficient structures is leading to the use of finite element analysis becoming far more widespread.

This book is intended to be an introductory text for new users of the software, many of whom will fall into one of two groups. Those who have a wealth of geotechnical engineering experience, but are relative novices in the art of numerical analysis and “young engineers” who have recently graduated from University and have typically spent a short time since graduation performing linear static finite element analysis. Some basic geotechnical aspects have been described and a glossary summarising the geotechnical terms (shown in bold italics) used in this booklet has been included. However, non-geotechnical engineers are advised to refer to other texts for a more detailed description.

Potentially there is a dangerous consequence of software becoming too easy to use in that such packages may be used completely as a “black box” without some knowledge of the underlying mechanics. As such, it is recognised that a need to understand the principles of the finite element method is required to help analysts in converting a real world problem into a representative finite element model. The aim of this booklet is to fulfill that need. It is assumed that the reader understands a little Finite Element jargon, including the terms such as node, element etc. If this is not the case, the reader is strongly advised to refer to other booklets such as ‘How to get started with Finite Elements’, ‘How to model with Finite Elements’ and ‘How to understand Finite Element Jargon’

Contents

1. Introduction

2. Background

3. Approaches For Geotechnical Analysis

• 3.1 Traditional Methods
• 3.2 Numerical Methods

4. Geotechnical Concepts

• 4.1 Spring-Dashpot Model for Soil
• 4.2 Effective Stress Analysis
• 4.3 Total Stress Analysis
• 4.4 Dry and Wet Unit Weights
• 4.5 Pore Fluid Pressures
• 4.6 Drained Analysis
• 4.7 Undrained Analysis
• 4.8 Groundwater Flow Analysis
• 4.9 Consolidation Analysis
• 4.10 Sign Convention

5. Modelling Concepts

• 5.1 Plane Strain Analysis
• 5.2 Axisymmetric Analysis
• 5.3 Three-Dimensional Analysis
• 5.4 Non-Soil Structural Components
• 5.5 Interfaces
• 5.6 Modelling Construction and Excavation
• 5.7 Undrained or Consolidation Analysis
• 5.8 Failure Mechanism and Factor of Safety
• 5.9 Geometric non-linearity

6. Soil Modelling

• 6.1 Mohr-Coulomb
• 6.2 Drucker-Prager
• 6.3 Cam-Clay and Modified Cam Clay
• 6.4 Choice of Material Model

7. Worked Examples

• 7.1 Smooth Rigid Strip Footing on an Elastic Soil
• 7.2 Smooth Rigid Strip Footing on an Elastoplastic Soil
• 7.3 Drained Excavation of a Building Pit in Sand

Glossary

Bibliography

Appendix 1: Effective Stress and Pore Pressure Calculation