Moving Critical and Phase-Transformation Stress State Lines of Saturated Sand During Undrained Cyclic Shear

Abstract

A new formulation is presented for realistically modeling the mobilized maximum stress and phase-transformation stress states of saturated sands subjected to cyclic undrained shear on the basis of analysis of laboratory tests. It was found that, with the development of induced shear strain, the effective stress path associated with positive dilatancy asymptotically moves in parallel with and tends toward the critical stress state line. Such a material response is quantitatively described as a Moving Critical Stress state Line (MCSL) and a Moving Phase-Transformation Line (MPTL). It has been shown that 1) MCSL and MPTL are two straight lines fixed in the moving stress space whose coordinate origin is shifted along the normal stress axis by a “reference stress” pr’, 2) the reference stress pr is a hyperbolic function of an “accountable shear strain increment”∆ γα and is dependent on the initial density; and 3) the slope of MCSL depends mainly on the initial relative density, while that of MPTL is independent of the density for a given sand. This formulation is further confirmed to be also suitable for irregular cyclic loading conditions.