Abstract: The strength and deformation behavior of granular soil have an important influence on the safety and stability of earth-rock dams, slopes and subgrade. For the strength and deformation behavior of granular soil under complex stress state, a state-dependent bounding surface plasticity model was established for granular soil by incorporating the state parameter and dynamic critical state line in the framework of the bounding surface plasticity theory and the critical state theory. The established model can not only predict the strain hardening and volumetric contraction, but also well describe the strain softening and volumetric expansion behaviors. Based on the secondary development platform of ABAQUS, the UMAT subroutine of the bounding surface plasticity model was developed by using the modified Euler integration algorithm with error control. The accuracy and convergence of the modified Euler integration algorithm were analyzed with different strain increments and integration error tolerance values. Finally, the rationality of the modified Euler integration algorithm with error control applied to the bounding surface plasticity model was verified by simulating the triaxial drained shear tests of granular soil under different densities and pressures, which laid a foundation for further engineering application.

Key words: granular soil, bounding surface, state-dependent, modified Euler integration algorithm, UMAT