Research On Coarse Granule About Its Stress Reacting To The Structural Changes In The Process Of Shearing

Coarse particles have a good engineering characteristics and it is also an important component of debris flow.As a kind of discontinuous material,the structural characteristics of the coarse particles greatly affect on its mechanical properties.When loading on it,the changes between the structure and the stress show dynamic response.Finding out indicators that can represent macro and micro structural characteristics of coarse particles.Discussing the relationship between stress and structural changes of coarse particles during the process of shearing.It is conducive to optimizing the constitutive model of coarse particles,monitoring the structural features to describe the stress state,and then evaluating the structural safety of coarse particles.In this thesis,the structural characteristics and mechanical effects of coarse particles are discussed based on previous research results.According to the composition of particle size and the shape outline of coarse particles,the coarse-grained soil is divided into four basic structure types: skeleton-gap structure,skeleton dense structure,mosaic structure and suspended dense structure.Based on the structural characteristics and its quantitative indicators which previous researchers has found about the coarse grained soil,fractal dimension is used as a comprehensive quantitative index to describe the structure of granular materials.In order to get the structural characteristics of particles in the shearing process conveniently,3 kinds of skeleton structure particles were selected to design direct shear tests in laboratory.The fractal dimension of the outline shape of the particle structure during the shearing process was calculated by MATLAB software,and the law of fractal dimension changing with stress were discussed.Studying the responsing relationship between the stress and the structural change during the shearing process of coarse particles by this.(1)According to the physical properties of the particles themselves and the composition characteristics of the bulks,the type of particle structure is summarized as four basic types: skeleton-gap structure,skeleton dense structure,mosaic structure and suspended dense structure.(2)The morphology parameters,shape index and volume fullness are used respectively for describing the particle shape,and the roughness of the particles for describing the particle surface,both be part of microstructure.The particle size distribution,the surface contact characteristics between particles and the particle arrangement characteristics are used for describing the macroscopic structural characteristics of the particles.The influence factors of the shear strength that coarse-grained soil are further analyzed through the description of the whole structure and structural characteristics of the single particles of coarse-grained soil.The mechanical effect of coarse grained soil depends on its particle size,particle shape,distribution of particles and the surface properties of particles,it is also closely related to the composition of particulate matter.(3)Summarizing kinds of quantitative indexes of particle size,shape,surface characteristics and spatial arrangement of the single particles,as well as the quantitative indexes of particle size distribution,particle contact state and the degree of particle breakage are proposed by predecessors.However,there are many kinds of evaluation indexes,and most of them only focus on one aspect.According to the fractal characteristics of the particle structure,fractal dimension is used as a fractal quantitative index to describe the general structural characteristics of the particles.(4)By direct shear test using 3 kinds of 10 ? 20 mm single grade coarse grained soil without viscous fine particles,the strength characteristics and shearing strength parameters of coarse-grained soil were obtained.The motion characteristics of the particle during shearing are obtained by the digital image processing technology,analysing the spatial distribution characteristics of the particles before and after shearing,and the ordering of the particles is described with the probability entropy.(5)The MATLAB software is used to deal with the images obtained in the direct shearing process,and calculate the fractal dimension of various particles in different stress states,so the relationship between the stress value,shearing strength,shearing strength parameter,residual strength and the fractal dimension value is discussed.And a simple numerical simulation using PFC2 D is carried out to verify the test results.