Study On The Mechanical Properties And Constitutive Model Of Soil-Rock Mixture

Since the 21 st century,with the rapid development of chinese domestic economy and the continuous improvement of people's living standards,the development and construction of urban infrastructure is getting faster and faster.The requirements for the stability of foundations such as buildings,roads,bridges and subway high-speed trains are also getting higher and higher.However,in some areas of southwest China,due to the impact of topographic conditions,a large number of soil-rock mixture are distributed with uneven grain size change,and the complex particle composition.It is one of the important research topics to understand the mechanical properties of soil-rock mixture and effectively determine the strength and deformation characteristics parameters of soil-rock mixture.The thesis takes the soil-rock mixture in the area of Baihetan Hydropower Station in Sichuan Province as the research object.Through the indoor medium-sized direct shear tests,discrete element numerical simulation and theoretical analysis,the strength and deformation characteristics of soil-rock mixture are studied,and the following main research contents are obtained:1.The indoor medium-sized direct shear tests are carried out on natural soil-rock mixture and saturated soil-rock mixture respectively,and it is concluded that the strength failure modes of the soil are all strain hardening types.The vertical pressure has a greater influence on the peak value of shear stress.With the increase of vertical pressure,the peak value of shear stress also increases,and the shear strength also increases.With the increase of stone content,the peak value of shear stress of soil-rock mixture appears the trend of decreasing after increasing,but the peak value of the shear strength of the saturated soil-rock mixture is smaller than that of the natural soil-rock mixture.With the increase of the stone content,the cohesive force first decreases and then increases and then decreases the trend of change,the internal friction angle shows a trend of increasing first and then decreasing.2.Through the discrete element numerical simulation studying on the soil-rock mixture,the main conclusions are: the discrete element numerical simulation is carried out on the indoor medium-sized direct shear tests scheme,and the numerical simulation results are compared and analyzed with the indoor test results.It is suitable for discrete element numerical simulation parameters of soil-rock mixture;the simulation parameters of the numerical test obtained by the indoor direct shear test are used as the meso-parameters for simulating the triaxial test.The simulation effects of the rock-bearing soil-rock mixtures are all good.The curve change rule is consistent with the macro tests change rule,and reliable strength and deformation parameters are obtained.3.The Duncan-Zhang model and the modified Cambridge model are respectively used to analyze the applicability of the stress-strain relationship of the soil-rock mixture.The main conclusions are that compared with Duncan-Zhang model,the modified Cambridge model is better in simulation the relationship between deviatoric stress and axial strain,and the two models are generally applicable to the stress-strain relationship of the soil-rock mixture.4.Based on the nonlinear strength criterion,the modified Cambridge model is improved,and a new elastoplastic constitutive model is derived.The model deduced in this paper is based on the modeling idea of the modified Cambridge model,and its dilatation equation is modified to better reflect the dilatancy characteristics of the soil-rock mixture.The model has many parameters,which are determined by curve fitting or laboratory tests easily.5.The numerical results of the new modified constitutive model are compared with the results of the triaxial simulation test of the soil-rock mixture.The following conclusions are drawn: compared with the modified Cambridge model,the new elastoplastic constitutive model is more effective in verifying the relationship between deviation stress and axial strain.