Plasticity modeling of the effect of sample preparation method on sand response

Abstract

Experimental evidence shows that different preparation methods produce sand samples with distinctly different stress-strain response. This paper explores and draws conclusions from the measured differences on the monotonic undrained triaxial response of Toyoura sand, prepared by different methods at the same values of void ratio and initial effective stresses. This is achieved by comparing data and simulations performed with a recently developed plasticity constitutive model, which accounts for the effect of inherent fabric anisotropy on the mechanical response. The inherent fabric anisotropy is represented by a second order symmetric fabric tensor, and its effect on the response at different loading directions is expressed by an appropriate dependence of certain constitutive ingredients on a joint isotropic invariant of the loading direction and the fabric tensor. Use of this constitutive scheme to simulate the aforementioned data on Toyoura sand exploits the fact that the preparation method affects both the dilatancy and the hardening response in a systematic manner. Under the premise that these effects are due to the different inherent fabric created by the preparation method, it follows that the foregoing simulations do not require changes in constitutive equations or entirely different sets of model constants. On the contrary, only model constants related to this inherent fabric anisotropy scheme need readjustment, providing insight to how the sample preparation method affects the response and what can be done to model it.