Some applications of Cam-clay in numerical analysis
The research described in this thesis investigated some applications of Cam-clay in numerical analyses. Single element analysis using the program CASIS was conducted to model undrained and drained triaxial compression tests to investigate the relative importance of the critical state soil parameters and streis history on the calculated soil behaviour. The values of these parameters covered the range of most commonly occurring natural soils. The investigation was extended to finite element modelling of plate loading tests using the computer program CRISP to examine the relative importance of the critical state soil parameters and stress history on the calculated undrained plate-soil behaviour. The capability of finite element coupled consolidation analysis of boundary value problems was demonstrated by the simulation of laboratory hydraulic fracturing experiments. The effects of rate of cavity water pressure increase, bore size, confining pressure and overconsolidation ratio on fracturing pressures were examined. The results of the parametric study of triaxial compression tests and plate loading tests were quantified in terms of stiffness (or tangent modulus), strength (or bearing pressure) and strain (or settlement) at the initial, yield, peak and ultimate states in the stress-strain (or pressure-settlement) response and allowed the comparison of these quantities for changing values of the soil model parameters. The studies revealed that the parameter x/A was the most influential because the initial states of soil were dependent on the values of ic and A and this dependence affected the subsequent stress-strain behaviour. In the prediction of movements of soil structures, the parameters x, A and a' are the most influential and their values should be critically evaluated for input in numerical analyses. In prediction of stability, the values of x, A and M are the most important ones. The work showed that the hydraulic fracturing phenomenon can be modelled by finite element coupled consolidation analysis. The computer program CRISP was validated against closed-form solutions and was found to predict the hydraulic fracturing phenomenon with a reasonable. degree of accuracy when the results were compared with the experimental data obtained by Mhach (1991). It was found that the rate of cavity water pressure increase had a significant influence in the prediction of fracturing pressure. The confining pressure was an important factor whereas the effects of bore size and overconsolidation ratio had some effects but were not as significant as the first two.