Fully undrained cyclic loading simulation on unsaturated soils using an elastoplastic model for unsaturated soils

Veerayut Komolvilas,Mamoru Kikumoto,P Delage,A.-M Tang,S Ghabezloo,J.-M Pereira,Y.-J Cui

doi:10.1051/e3sconf/20160917008

Veerayut Komolvilas, Mamoru Kikumoto + Show 5 more

Open Access

https://doi.org/10.1051/e3sconf/20160917008

Copy DOI

Abstract

Several researchers have reported that Bishop’s mean effective stress decreases in unsaturated soils under fully undrained cyclic loading conditions, and unsaturated soils are finally liquefied in a similar manner as saturated soils. This paper presents a series of simulations of such fully undrained cyclic loading on unsaturated soils using an elastoplastic model of the unsaturated soil. This model is formulated using the Bishop’s effective stress tensor incorporating the following concepts: the volumetric movement of the state boundary surface containing the normal consolidation line and the critical state line due to the variation in the degree of saturation, a soil water characteristic curve model considering the effect of specific volume and hysteresis, the subloading surface model, and Boyle’s law. Comparisons between the simulation results and the experimental ones show that the model agreed well with the unsaturated soil behavior under cyclic loading. Finally, the typical cyclic behavior of unsaturated soils under fully undrained conditions, such as the mechanism of liquefaction of unsaturated soils, the compression behavior, and an increase in the degree of saturation, are described through the proposed simulation results.

Highlights

Soils are often subjected to a cyclic loading under unsaturated conditions in actual fields such as the deformation of embankments and reclaimed grounds during an earthquake
All the studies reviewed here support the hypothesis that the mean value of the Bishop's effective stress of the unsaturated soil gradually decreases under fully undrained cyclic loading conditions and the soil is liquefied in a similar manner as the saturated soil
The decrease in the effective stress under fully undrained cyclic loading is caused by an increase in pore-air and pore-water pressures, and the liquefaction of the unsaturated soil will occur when both air and water pressures reach the initial value of the total confining pressure [5]

Summary

Introduction

Soils are often subjected to a cyclic loading under unsaturated conditions in actual fields such as the deformation of embankments and reclaimed grounds during an earthquake. The main purpose of this paper is to present a series of simulations of fully undrained cyclic loading on unsaturated soils using an elastoplastic constitutive model for unsaturated soils [9] This model is formulated using the Bishop's effective stress tensor incorporating the following concepts: the volumetric movement of the state boundary surface containing the critical state line due to the variation in the degree of saturation, a soil water characteristic curve model considering the effects of specific volume and hydraulic hysteresis, the subloading surface model, and Boyle's law. The typical cyclic behavior of unsaturated soils under fully undrained conditions, such as the mechanism of liquefaction of unsaturated soils, the compression behavior, and an increase in the degree of saturation, are described through the proposed simulation results

Basic concepts

Elastoplastic stress-strain relationship for unsaturated soil

Simulations

Conclusion