Mathematical modelling of cyclic behaviour of soils

SYNOPSIS : A constitutive law which may describe the behaviour of either clay or sand under cyclic loading is presented. The proposed constitutive model combines an elasto-plastic constitutive law which belongs to the family of the models extended from Cam Clay and a suitable piecewise path independent law, valid within the current yield locus, which was especially conceived to model the hysteretic behaviour of soils. The model allows a better understanding of the decay of undrained cohesion of a normally consolidated clay on the type of test, the number of pre-shearing cycles, the intensity of the cyclic loading. The predictions concerning the variation of pore pressures and shear moduli with number of cycles are discussed. Moreover, it is shown that the same model may describe the behaviour of a sand under cyclic loading at constant strain or stress amplitude, and consequently the prediction of the number of cycles necessary to cause liquefaction is possible.