Research On Analytical Constitutive Model Of Rockfill Material Based On Microstructure Contact Theory

As a common dam type, earth-rock dam is widely used in hydraulic projects for its advantage of low investment, relatively simple construction technique, short construction period and low requirement for topography and geological conditions. However, rockfill material shows very complicated behavior. Its properties of nonlinearity, elasto-plasticity, dilatancy, rheological behavior, strain hardening or strain softening and anisotropy are the key features to establish the constitutive model for rockfill material.By far, most of the models in application are established based on macro-phenomenological theory. They cannot account for the nature of rockfill’s strength, deformation and failure for their lack of microstructural analysis, which limits their wider application. Analytical constitutive model of rockfill material based on microstructure contact theory can well describe the mechanical behavior of rockfill and this approach reveals the microcosmic mechanism of rockfill’s deformation and strength development. Some work based on this theory are as follows:1) The theoretical framework of rockfill’s microstructural analytical model is established. The local behavior is assumed to follow Hertz’s elastic law and a Mohr-Coulomb’s plastic law. The hardening function is defined by a hyperbolic curve in k-△αp plane. The interlocking influence is described by packing void ratio affecting the peak friction angle between neighboring particles. The macro-micro relationship between strain and inter particle displacement for an assembly is derived by using "best fit hypothesis" and then the macro-micro relationship between stress and inter particle contact force is obtained by using principle of complementary energy conservation. Finally, the relationship between stress and strain is obtained.2) The main parameters are determined through two methods:some parameters which have relatively clear physical meanings are derived from experimental results and the other parameters which are relatively empirical can be selected by Particle Swarm Optimization method. In this paper, the numerical simulation of conventional triaxial compression test for three kinds of different rockfill material are presented. 3) To establish a more clear cognition of the main parameters, the sensitivity analysis is conducted. The results reveals the influence on numerical simulation of every main parameter. Also, we summarize some simulation experience and the potential ability of this model is predicted.4) Exploration in simulating more complicated experiment is carried out. According to experimental results under paths of constant stress ratio, a new initial hardening stiffness and some other hypothesises are assumed. Then we simulated the stress-strain relationship of experiment under paths of constant stress ratio.