The Macro And Meso Mechanical Characteristics And Nonlinear Elastoplastic Constitutive Model Of Soil-rock Aggregate

In recent years,with the continuous expansion of Chinese infrastructure construction,a lot of ultra-high fill projects have emerged in the complex-geological southwest area of China where some airports in mountainous region are newly built or expanded.In these projects,soil-rock aggregate is widely used which is complexly formed in geology,diversely constituted in ingredient and extremely uneven in structure.Thus,the correct evaluation of stability of the high fill slope which is formed in soil-rock aggregate has become one of the main problems to be solved.In this paper,a high fill slope project built on an airport in southwest mountain area is concerned based on a development project of"the key construction technology of subway tunnel crossing under the backfill area deeply and longly in mountain city"sponsor by China Railway Science and technology of Limited by Share Ltd.Through the laboratory test,theoretical analysis and numerical simulation,the macro and micro shear strength characteristics of the soil-rock aggregate and its shear strength generation mechanism,shear deformation characteristics and constitutive model,the stability of the high embankment slope are systematically and thoroughly researched.The main research contents and achievements are as follows:?1?The large scale direct shear test,sieve test,acoustic emission test and three-dimensional laser scanning test of shear surface are conducted to study on the macro shear mechanics properties of the soil-rock aggregate in Chongqing area,such as diverse rock contents P₅,moisture contents w,rock lithology R_c,intial void ratios e₀ and stress conditions?_n.The variation law of particle breakage and relative breakage rate,the particle breakage developing law of shear process,the three-dimensional feature of shear surface and the fractal law of the soil-rock aggregate are obtained.?2?Based on the results of direct shear test of the soil-rock aggregate,shear strength and strength parameters are researched.It is shown that the shear strength can not completely satisfy the linear M-C strength criterion,but meet the modified M-C nonlinear strength criterion,and the nonlinear characteristic is related to the particle breakage.With the influence of the rock content,water content,rock lithology,initial void ratio and so on,the variation law of cohesion,initial internal friction angle and nonlinear internal friction angle are obtained.?3?Based on the numerical simulation of the particle flow code in the direct shear test,the meso shear behavior and the strength generation mechanism of the soil-rock aggregate with different rock contents are studied.In details,the strengths and weaknesses of formation of the 3 blocks i.e.Ball,Clump and Cluster are comparatively analyzed.In the shear process,the particle movement and its breakage law,the rupture evolution of the contact bond,the crack development,the evolution of energy conversion,the shape and evolution of the shear surface,the distribution and evolution of the contact force are acquired,which can be mutually verified and replenished with the experimental results of the direct shear test results.Combined with the fractal law and the force chain distribution of the shear surface,formulas of the strength generation mechanism are deduced,and then the variation law of the strength parameters of the indoor direct shear test are explained.?4?With the large scale triaxial test,the consolidation rebound deformation properties and the triaxial shear stress and strain characteristics of the soil-rock aggregate with different rock contents are studied.Under the conditions of different rock contents of the soil-rock aggregate,the law of body strain-stress compression and springback,the relationship between deviatoric stress and shear strain,the relationship between volumetric strain and shear strain are obtained.The energy equation considering particle breakage is established.According to the elastic-plastic incremental theory and nonlinear strength criteria,a nonlinear elastic-plastic constitutive model of soil-rock aggregate with different rock contents is deduced.It is verified that the model can adaptively simulate the stress-strain relationship of the soil-rock aggregate.?5?Based on the finite difference theory,the expressions of nonlinear elastic-plastic constitutive model are deduced.Using the fluent secondary development platform of FLAC^3D and the VC++6.0 program,a procedure of the nonlinear elastic-plastic constitutive model is developed,and the dynamic link calculation program of the model is realized,and the correctness of the procedure is verified by the experimental results.?6?The strength reduction method is adopted to put forward the definition method of safety factor of the soil-rock aggregate in the high fill slope when using the nonlinear elastic-plastic constitutive model.The energy mechanism of material damage in thermodynamic theory is introduced in slope engineering,and a procedure of several slope failure criteria based on energy catastrophe witch can applied to complex three-dimensional high fill slope is developed with FLAC^3D.Then,the three-dimensional numerical model of the high fill slope is built in FLAC^3D.Based on the strength reduction method,the developed procedure of nonlinear elastic-plastic constitutive model and energy criteria are used in evaluate the slope stability.the influence of rock content,water content,rock lithology,initial void ratio on the slope stability are analyzed.