Research Of Critical State Characteristics Of Rockfill And Constitutive Model Of Particle Breakage

Under the action of self-weight and huge water load,rockfill particles break up,which significantly affects its stress-strain behavior.The data of conventional triaxial tests with high quality and axial strain of about 25%are scarce,which makes it difficult to derive the constitutive model and determine the parameters of the model.The test data under low confining pressure will lead to smaller dam deformation,which is not conducive to the safety assessment of the dam.Therefore,the study of constitutive model of particle breakage under conventional triaxial stress path has become a hot issue in recent engineering.In this paper,taking Shu ibuya dam as an example,the stress-strain characteristics of rockfill materials are studied by conventional triaxial tests,and a constitutive model considering particle breakage of rockfill materials is constructed.The main work of this paper is as follows:1)A large-scale triaxial test of the dam material of Shuibuya Dam,the highest concrete face rockfill dam in the world,was carried out.Nine new and more accurate stress and strain data were obtained,and the conventional triaxial test data obtained are reviewed.2)Based on the analysis of high-quality triaxial test data,the stress-strain law of granular crushed rockfill material is obtained,including:It is verified that:（1）The logarithm of mean principal stress P is linear with the ratio of pore ECS in critical state;（2）The relationship between critical state shear stress q and mean principal stress P is power function.（3）The relationship between the friction angle of rockfill and the particle breakage rate satisfies the power function.With the increase of the breakage rate,the internal friction angle decreases.It is found that:（1）Particle breakage B_r is power function with confining σ₃;（2）Critical state stress ratio M_f is logarithmic with confining σ₃.（3）The predicted results of the formula show that the rock-fill material will also break up to a certain extent under high confining pressure,but it is far less intense than imagined.3)It is proposed for the first time that the"volume change invariability"is the best criterion for judging whether the rockfill material with a large number of particle breakage under high confining pressure meets the critical state criterion,and the"shear stress invariability"criterion in the traditional critical state theory is abandoned.4)The Wan and Guo formulas previously proposed by the laboratory were checked and revised.After introducing the particle breakage correction term,the fitting effect of triaxial data under medium and high confining pressures is better.The particle breakage law of rockfill under triaxial stress path is studied.5)On the basis of absorbing the existing theory and improving the relevant constitutive model,a fitting formula is proposed to modify the original Duncan-Chang model,and an elastic non-linear constitutive model for particle breakage is proposed.