Critical State Soil Mechanics for Cyclic Liquefaction and Postliquefaction Behavior: DEM study: Fid-Bau Portal

Critical State Soil Mechanics for Cyclic Liquefaction and Postliquefaction Behavior: DEM study

Rahman, M. M. / Nguyen, H. B. K. / Fourie, A. B. / Kuhn, M. R.

Discrete-element method (DEM) simulations of three-dimensional (3D) assemblies of ellipsoid particles were used to evaluate the critical state (CS) for both drained and undrained (constant volume) conditions. A series of conventional triaxial cyclic liquefaction tests with symmetrical cyclic deviatoric stress ( $σ_{d}$ ) with initial $q = 0 kPa$ were simulated to develop a relationship between the cyclic stress ratio ( $C S R = σ_{d} / 2 σ_{0}^{'}$ ) and the number of cycles required for initial liquefaction ( $N_{L}$ ), where $σ_{0}^{'}$ is the mean effective normal stress at the end of consolidation. Both cyclic mobility and instability type behaviors were observed depending on the initial void ratio ( $e_{0}$ ) and $σ_{0}^{'}$ . The micromechanics quantities, i.e., the coordination number ( $C N$ ), von Mises fabric ( $F_{v M}$ ), fabric anisotropy intensity ( $α_{c}$ ), and stress-strain behavior, suggested that cyclic mobility and instability may depend on the phase transformation and instability state, respectively. The cyclic resistance ratio ( $C R R_{15}$ ), i.e., $C S R$ at $N_{L} = 15$ , showed a unique relation with the initial state parameter ( $ψ_{0}$ ), irrespective of $e_{0}$ and $σ_{0}^{'}$ . Two series of postliquefaction monotonic simulations with and without reconsolidation exhibited a unique CS, which perfectly matched with the original CS line. The $F_{v M}$ also reached a unique, narrow range at the CS. The postliquefaction settlement during reconsolidation also showed a linear relation with $ψ_{0}$ .