Abstract:
The stress strain behaviour of soil is reviewed. A mathematical model is presented to study the stress strain behaviour of over consolidated soil. The model is a macroscopic model, developed from a constitutive relation for a work hardening plastic material. The critical state concepts are introduced as a framework for the description of the observed soil stress strain behaviour. Mathematical expressions are formulated to describe the observed soil stress strain behaviour. These expressions result in the functions required by the constitutive relation. The soil model is presented in terms of a three dimensional principal stress system. The soil model is assessed by comparing the model predictions with the results from laboratory apparatuses. The comparison is made for soil tested in the oedometer, the triaxial cell, the biaxial apparatus and a true triaxial apparatus. A finite element method of analysis is developed to study continuum problems in geomechanics. A two dimensional, parabolic isoparametric element is used. A frontal solution algorithm is programmed to solve the simultaneous equations. The nonlinear load deformation history is analysed with a Euler incremental solution procedure. A two dimensional (plane strain and axisymmetric) version of the soil model is formulated as the material law for the finite element program. This finite element program is used to study continuum problems, a shallow tunnel in soft clay and several well documented embankment trials. Comparisons are made between the predicted and measured values for the prefailure deformations and pore pressures. The predicted stress paths in the continuum are examined. For many civil engineering problems the expense of a finite element analysis is not warranted. The stress path method is introduced as a simpler alternative to the finite element method An appropriate stress path for the foundation is postulated and the soil model is used to integrate the strains for that stress path.