Abstract: In order to get accurate numerical simulation parameters of the modified Mohr coulomb model, based on a deep foundation pit engineering example, each soil layer of soil samples of a deep foundation pit was taken to carry out the triaxial shear test, unloaded-load test again and consolidation test, respectively, under different confining pressure. The secant modulus and unloading elastic modulus were obtained from the stress-strain relation curve, following the comparison between the model parameters and compression modulus. It can be concluded that:under different confining pressures, the silty soil in the test is softened. Under the confining pressure of 200 kPa, there was no peak point in the effective deviation-strain curve of fine sand, showing hardening failure. Before the soil is damaged, the stress-strain curve form of the soil is hardly affected by the process of unloading and reloading, with nearly the same unloading and reloading modulus before and after the obtained deviant stress peak point. The tangent modulus, secant modulus, and compression modulus of the test silty soil are approximately equal. With the increase of the reference stress, the ratio of the unloading modulus to the compression modulus increases in a quadratic function. The accuracy of the parameters is verified by numerical simulation, so experimental research is an important way of parametric precision.

Key words: modified mole coulomb model, soil parameters, experimental research, unloading die, numerical modeling