7.1 Introduction

The mechanical behaviour of soils may be modelled at various degrees of accuracy.Hooke's law of linear，isotropic elasticity，for example，may be thought of as the simplest available stress⁃strain relationship.As it involves only two input parameters，i.e.Young's modulus，E and Poisson's ratio，ν，it is generally too crude to capture essential features of soil and rock behaviour.For modelling massive structural elements and bedrock layers，however，linear elasticity tends to be appropriate.