By using state-dependent yield function and dilatancy function

a state-dependent non-associated elasto-plasticity hardening model is proposed to simulate the undrained behaviors of saturated soils with different initial densities and confining pressures. According to the second-order work theory

the criteria for potential instability and static liquefaction of saturated soils are proposed. The proposed model and criteria were employed to predict a series of undrained triaxial tests on loose sands. The results showed that the static liquefaction occurs at the hardening stage before the plastic limit

the onset of static liquefaction accompanies with the peak of shear stress; and then the pore water pressure increases and the shear stress decreases with further loading. The stress-strain relationship of the municipal solid waste under undrained condition was also analyzed; the potential instability line was obtained and the onset of static liquefaction was predicted.