A finite element study of the pressuremeter test in sand using a nonlinear elastic plastic model

The stress–strain behaviour of sands is highly nonlinear, even at stresses well below the peak strength of the sand. The hyperbolic model is a reasonable conceptual model for representing the stress–strain behaviour of sand, but some empirical curve fitting is required to obtain a more realistic model for calculation purposes. This can readily be performed for reconstituted samples of sand using laboratory tests. Recent evidence shows that the stiffness of natural sands is often much greater than that of the same sand when reconstituted at the same density and stress state in the laboratory, and it is therefore necessary to use in situ testing methods to determine the stress–strain behaviour of such sands. In this paper, the finite element method is used to simulate pressuremeter tests in a soil modelled using a hyperbolic-type model. It concentrates on the behaviour in unload-reload loops, which are often included in pressuremeter tests to measure shear modulus. The effect on the whole unload-reload loop of varying some of the model parameters is examined. The results are compared with a high-quality pressuremeter test in sand. It is concluded that, though the results to date are encouraging, some further experimental work is required to verify some of the features of the model. Key words : pressuremeter test, hyperbolic model, nonlinear behaviour, initial shear modulus, sand behaviour.