Experimental And Numerical Investigation On Shear Behavior Of Mixed Soil

The thesis presents a study of the effect of gravel content(GC)on simple shear behavior of sand-gravel mixture and silt-gravel mixture.The test shows that the sand-gravel mixture and the silt-gravel mixture have great differences in strength and deformation properties,but both show the threshold of gravel content in shear behavior,that is,before the threshold gravel content,the shear strength of the soil-rock mixture increases with the increase of the gravel content,and after the threshold,the shear strength decreases with increasing gravel content.The phenomenon of gravel content threshold is analyzed from the change of porosity of soil-rock mixture,then a formula to calculate the gravel content threshold is proposed.A two-dimensional discrete element simulation was later established for the sand-gravel mixture,and the variation of contact anisotropy coefficient under different shear strains is analyzed.It was found that with the increase of the shear stress of the sand-gravel mixture,the main direction of the contact force chain in the sample is gradually biased toward the shear direction,and the contact anisotropy amplitude is also gradually increased.Subsequently,the variation of the internal force chain structure was studied.It was found that when the gravel content is less than the gravel content threshold,the increase of gravel content helps to form a strong contact force chain skeleton,which can effectively improve the shear strength of the sample.After the threshold,since the contact force skeleton has been formed,increasing the gravel content has little effect on the strong contact force skeleton,and the support of the weak contact chain for the contact skeleton is reduced because of the reduction in the number of particles,which leads to a decrease in the shear strength of the sand-gravel mixture.A three-dimensional discrete element model of a sand-gravel mixture was established and compared with the experimental results,to overcome the limitations of the two-dimensional discrete element model.Quantitative analysis was conducted of the effect of gravel content on the probability density distribution of the strong and weak force chain inside the sand-gravel mixture.The statistical interpretation of the gravel threshold phenomenon is obtained and the friction mobilization inside the sand-gravel mixture is analyzed from the point of view of friction mobilization rate.