Numerical investigation of diffuse instability in sandy soil using discrete element method under proportional strain path loading

Abstract

The Loose sandy soil can manifest static liquefaction phenomenon under undrained condition, in which the onset of instability is within the failure line, and there is no obvious shear band. This type of failure mode, very different from localized instability that occurs in dense sand, is called the diffuse instability. In this paper, a series of proportional strain tests and fully drained tests under different initial void ratio were simulated using the discrete element method. The influence of strain increment ratio and the initial void ratio affecting the instability of sandy soil were discussed in detail. The development mechanism of pore water pressure in proportional strain tests was analyzed by comparing with the volumetric curve of fully drained test. Finally, a unified mechanism of diffuse instability of sandy soil in proportional strain tests was explained. Numerical results indicate that the strain increment ratio and the initial void ratio work together affecting the instability of specimen. The occurrence of diffuse instability is the result of effective stress reduction due to the development of pore water pressure, which depends on the difference of volumetric strain between fully drained tests and proportional strain tests. The increment of pore water pressure is determined by the difference of strain increment ratio, which can be used as an index to reflect the liquefaction potential of sandy soil.