The failure modes of granular material in undrained cyclic loading: a critical state approach using DEM

Cyclic liquefaction failure modes are directly related to the consequence of liquefaction and important for mitigation strategies. Two common failure modes, cyclic mobility (CM) and cyclic instability (CI), are well reported in the literature. However, recent experimental studies revealed three other failure modes, i.e. plastic strain accumulation (PSA) and two hybrid failures: CI followed by CM and CI followed by PSA. This study used discrete element method (DEM) which demonstrated all five different failure modes for cyclic loadings. The mechanics involved in these failure modes were evaluated in light of the Critical State Soil Mechanics (CSSM) framework using a series of drained and undrained triaxial simulations after isotropic and K-0 consolidation. The state parameter (psi) showed a good correlation with phase transformation (PT) and instability (IL) states. It was found that cyclic failure modes, particularly CM and CI, are closely linked with the PT and IL states, respectively. Some previous studies reported that the hybrid failure mode depends on the soil fabric influenced by the sample preparation method. However, all five different failure modes were observed for the assemblies prepared by the same technique. It was found that the failure modes depended on the location of the initial states of soil with respect to the critical state line in the classical e-log(p & PRIME;) space, where e is the void ratio and p & PRIME; is mean effective stress. Also, distinct zones for failure modes were observed in the SSR/CSR-psi space, which confirmed that the cyclic behaviour was strongly dependent on psi; where CSR is cyclic stress ratio and SSR is static stress ratio. Such observation allows the prediction of cyclic failure modes within the CSSM framework.

Automated summary

Cyclic liquefaction failure modes are directly related to the consequence of liquefaction and important for mitigation strategies. Two common failure modes, cyclic mobility (CM) and cyclic instability (CI), are well reported in the literature. However, recent experimental studies revealed three other failure modes, i.e. plastic strain accumulation (PSA) and two hybrid failures: CI followed by CM and CI followed by PSA.