Abstract

This chapter presents a state-dependent elastoplastic constitutive model for both saturated and unsaturated rockfill materials. The model, which is developed within an extended critical-state framework, uses two independent stress state variables: total stress and total suction. The loading-collapse (LC) curve proposed by Oldecop and Alonso for unsaturated rockfills is used herein. A unified hardening parameter, which could consider the effects of stress level, internal state (density) and relative humidity, is introduced to describe the state-dependent dilatancy of saturated and unsaturated rockfill materials. The details of the model formulation and parameters determination are described and reported. Numerical simulations on the triaxial tests, such as the drained shear tests on the saturated specimens with different initial dry densities, shear tests on the specimens with different relative humidity and wetting deformation tests under constant vertical strain rate, have been carried out using the proposed model. The numerical results show that the stress-strain relationships at both loose and dense, saturated and unsaturated states can be properly modelled with a single set of parameters. Additionally, the proposed model can also capture some other key features such as the strain-softening behaviour at the dense state and low confining stress, the sudden stress relaxing subjected to the flooding under a constant vertical strain.

Highlights

  • It is well recognised from the experimental studies and engineering practice that the influence of water on the mechanical behaviour of rockfill materials is significant

  • Considering an isotropic compression test on unsaturated rockfills, in which a rockfill sample at a given relative humidity is subjected to p-load increments along virgin states, which is in full correspondence with the compression behaviour of saturated rockfills, the specific volume will be given by v 1⁄4 1 þ e 1⁄4 N À λðψÞp where ν is the specific volume, e is the void ratio and N is the intercept of the normal compression lines with the ν-axis when p = 0

  • The triaxial tests on the saturated specimens with different initial void ratio, triaxial tests with different relative humidity and triaxial wetting tests under constant vertical strain rate were simulated by means of a hexahedral element

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Summary

Introduction

It is well recognised from the experimental studies and engineering practice that the influence of water on the mechanical behaviour of rockfill materials is significant. By virtue of the assumption of coaxiality of the strain rate tensor and the stress tensor, the strain components are estimated and translated into nodal forces, which are further applied to the finite elements to obtain the wetting deformation of the dam This so-called single curve method is widely used in dam engineering in China due to its practicality. The purpose of this chapter is to present an elastoplastic model for unsaturated rockfill materials by introducing a unified hardening parameter which could well capture the essential physical phenomena behind the observed collapse deformation and state-dependent dilatancy for saturated and unsaturated rockfill materials. The comparisons are conducted using the experimental data from a series of triaxial tests on saturated and unsaturated rockfill materials, and the capability of the proposed model to capture the state-dependent behaviour and collapse deformation is validated

Basic constitutive variables
Normal compression model
Loading-collapse yield curve
Yield surface
Unified hardening parameter
Elastic moduli
Determination of model parameters
Model validations
Behaviour of rockfill compacted to various initial void ratios
Behaviour of rockfill with various RH
Behaviour of rockfill during shearing and wetting
Findings
Conclusions
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