Experimental And Theoretical Analysis Of Multi-scale Deformation Characteristics Of "Membrane Model" Soil

Soil is a special multi-phase material composed of solid particles,pore water and pore gas,with the basic characteristics of granularity and structure.Due to the different interaction modes between particles of different scales,complex micro-and microstructures are formed,resulting in huge differences in soil macroscopic deformation and strength characteristics,highlighting the multi-scale characteristics of soils.In this paper,a combination of experiment and theoretical analysis is used to study the multi-scale deformation characteristics of "membrane model" soil.First,the solid particles in the soil are divided into matrix particles(bentonite particles)and reinforced particles(quartz sand particles)according to the energy division criterion,and the "membrane model" soil which belongs to coarse-grained soil is formed when the volume ratio of reinforced particles(the ratio of the volume of reinforced particles to the total volume of the soil)is more than 0.4;based on the "membrane model" framework,a series of triaxial and direct shear tests are designed to analyze the physical mechanism of soil deformation and strength characteristics from microscopic and macroscopic;a multi-scale theory that conforms to the "membrane model" soil mechanical properties0 is established,and a fitting analysis of the test results is performed to verify the applicability of the multi-scale theory of the membrane model.The main research work and results of this paper are as follows:(1)The comparative test between the sampling method and the freezing method shows that the freezing method can not only ensure the integrity of the "membrane model" soil sample,but also will not have a major impact on its deformation and strength characteristics,which is a reasonable and feasible method of sample preparation for "membrane model" soil.(2)From the triaxial compression test results of the "membrane model" soil,it can be seen that with the increase of the strengthening particle content,the deformation of the soil exhibits softening characteristics,and the shear strength gradually increases;with the increase of the strengthening particle size Increasing,the deformation of the soil exhibits enhanced characteristics,and the shear stress gradually decreases;with the increase of dry density or the decrease of the intergranular gas phase void ratio,the peak stress of the soil increases.(3)From the direct fast shear test results of the "membrane model" soil,it can be seen that with the increase of the strengthening particle content,the cohesion of the soil shows a decreasing trend,and the internal friction angle shows an increasing trend;the increase or the decrease of the gas-phase void ratio between grains will increase the cohesion and internal friction angle of the soil;and the change of the reinforced particle size has little effect on the shear strength index of the soil.(4)The "membrane model" soil equivalent matrix membrane thickness is related to the reinforced particle size and matrix content,and can comprehensively reflect the characteristics of soil granularity and structure.With the increase of the equivalent matrix membrane thickness,the triaxial peak stress gradually decreases,and there is a strong correlation between the two.(5)The experimental analysis shows that the "membrane model" can describe the multi-scale deformation characteristics of the soil,and then a fitting analysis is performed on the results of the test by using the established formula of multi-scale theory,which is preliminarily verified that the model has good applicability and effectiveness to the soil with a large amount of reinforced particles.