Coarse Granular Soil Constitutive Model Incorporating Particle Breakage

The coarse granular soil is applied widely in rockfill dam, high way, railway, aerodrome and dyke, because of the engineering properties such as suitable compactibility, high hydraulic permeability, high density, high shearing strength, and small settlement. The coarse granular soil is susceptible to particle breakage in high compressive strength, which modifies its structure directly, influencing its dilatancy, friction angle, strength and permeability. With the height of the rockfill dam increasing, the coarse granular soil, which is the main material in dam engineering, suffer higher stress. Therefore the particle breakage of the coarse granular soil gets increasingly notable. The traditional constitutive model, incorporating no influences of particle breakage, is not appropriate to describe the stress and strain of the coarse granular soil under the high stress. In this paper, the particle breakage energy is incorporated in the energy formulation, on which the constitutive model for the coarse granular soil incorporating particle breakage is developed according to the energy fomulation.In this paper, the particle breakage rule and breakage energy are studied during triaxial shearing, on which the associated equation is established. Combined with the triaxial test, the friction coefficient formulation incorporating particle breakage is developed according to the energy balance during shearing, which determines the model parameters and verifies the correction of the model.The breakage parameters are studied and the test data are simulated in this paper, on which the relationship of breakage energy and breakage parameters is established. The breakage energy is introduced in the energy balance formulation during shearing. And the yield function is deduced with the application of associated flow rule. The hardening rule is developed according to triaxial test result, on which the constitutive model is developed. The parameters of the model are determined by the mutation particle swarm optimization algorithm according the triaxial test results. The model developed is proved to reflect the stress-strain-volume strain relationship comparing with the test curve.The shearing features of coarse granular soil are influenced not only by particle breakage but the inner states, on which the unassociated flow rules constitutive model is developed in this paper. With the adoption of the equal stress ratio yield function developed by Pender, the shearing yield features are described. And the flow rules are deduced according to the energy balance equation incorporating particle breakage energy. With the critical state line in v-p plane developed by Chavez, the difference between the current void ratio and the critical state void ratio corresponding to the current stress is determined to be the state parameter. The breakage energy and state parameters are introduced in the hardening rules developed by Wood, on which the strain-softening behavior of the soil can be described, and the coarse granular soil constitutive relationship incorporating the influence of the particle breakage and the inner state is established.In order to make up the associated flow rules constitutive model lacking in describing the state-dependent features, the relationship between model parameters and initial state parameters is developed, and the influence of the inner state on the shear features is introduced in the associated flow rules constitutive model developed. The initial state parameters are calculated with the critical state line established by Ishihara. Therefore, the relationship between initial state parameters and breakage parameters, and the relationship between initial parameters and hardening parameters are developed, which are determined by the triaxial test curve simulation. The triaxial curves in different initial states are calculated, verifying the validation of the model. The calculation results indicate that, the constitutive model developed can describe the shearing features of coarse granular soil in different initial conditions.