Quantitative Evaluation Of Coarse-grained Soil Structure And Its Structural Study Of Strength

In this paper,based on the field geological survey and the previous scholars'research results,the structural characteristics of coarse-grained soil with different genetic types are analyzed.According to the idea of coarse particle content evolution and contrasting the structure types summarized through geological origin,the classification of coarse grained soil structure is loose skeleton structure,dense skeleton structure,embedded structure,filling structure of four basic structure types.So as to study the strength characteristics of different structure shown,we design the corresponding laboratory tests and the particle flow code program are used as the tools to carry out the research on micromechanics of granular matter with different structures.The following conclusions are obtained:?1?according to the coarse soil genesis,particle composition,particle arrangement and contact law,the basic structure of the coarse grained soil type are summed up:skeleton structure,mosaic structure and filling structure.?2?according to the quantitative evaluation of coarse grained soil structure,a comprehensive analysis results is acquired.Based on the evolution characteristics of coarse particle content?P₅?and the force chain structure,as when P5=70%,the coarse grained soil structure as the skeleton structure;30%<P5<70%,coarse grained soil structure type for the embedded structure?mosaic structure?;P5=30%,the coarse grained soil structure type filling structure.For the skeleton structure,according to whether the pore is filled with fine particles,it can be further divided into skeleton dense structure and skeleton loose structure.?3?the strength characteristics of cohesionless coarse grained soil with different structure types are explored by designing the laboratory strength test.In the selection of artificial gradation of irregular shape particles as the sample material under the premise,the indoor medium direct shear apparatus is adapted.Finally we obtained the filling structure,embedded structure,skeleton dense structure,skeleton loose structure of the 4 kinds of curves of shear stress-displacement.Through the analysis of the stress-strain curve,eventually the strength indexes of 4 kinds of structure is got.Besides it found that the filling structure of cohesionless coarse grained soil samples has the smallest internal friction angle,the embedded structure and the skeleton dense structure internal friction angle increases gradually,the skeleton loose structure of internal friction angle appears decreasing trend.?4?By the particle flow code?PFC?to establish the model of numerical experiments,which are consistent with indoor test.Based on the simulation results agree well with the indoor test results,we found that the force chain evolution characteristics of each structure types under different vertical load force chain:?1?The filling structure is mainly fine-grained,and the coarse particles are separated from each other.In the dense state,the compression pore cell shape changes little,the porosity change is very small,the increase of load leads to the weak force chain into the strong force chain.So,the particle position adjustment is very small can only play through the particle itself strength to withstand external load;?2?Mosaic structure:the content of the coarse and fine particles in the mosaic structure is close.In the dense state,after the compression the change of the pore cell which were formed by strong force chain is small.the increase of the load will lead to the decrease of the number of weak force chain and the increase of the number of strong chain,then show that the increase in the strength of the strong force chain.That is,after the compression of fine particles to adjust the position of the formation of more weak chain to bear the load,with the further increase of the load,coarse particles through their own strength to withstand the role of external load;?3?The skeleton dense structure is mainly coarse particles,and the content of small particles is less.In the dense state,the change of the pore cell is small,the increase of the load will firstly lead to the increase of the strength chain,and then the number increase of the strong chain and the weak force chain into the strong chain.That is,after the pressure the variation of pore is very small,The coarse particles began to play their own strength to withstand the load,with the increase of load,adjusting the position of coarse particles to form a strong chain and more fine particles also play their own strength to withstand loads;?4?The skeleton loose structure is coarse.In the dense state,the pore cell changes obviously after compression.The increase of load leads to the number increase of the strong force chain.That is,after the compression of coarse particles by adjusting the location of the formation of a number of strong chain to withstand external load.?5?we found that the force chain evolution characteristics of different types of structures in the process of shearing:four kinds of structure with the increase of the content of coarse grain structure by filling structure evolution to loose skeleton structure,their force chain evolution have the similarities and differences of in the process of shearing:?1?The commons were that the four structures in the shear process,the weak force chain has been broken reconstruction constantly,strong chain along the diagonal direction of shear box concentration changes,and the peak after the show of force chain and fault reconstruction,to maintain a stable number of boxes to the diagonal direction along the shear strength of chain.?2?The differences were that before the peak,the filling structure mainly by adjusting the position of the fine particles to increase the number of strong chain to increase the shear strength;Before fitting the peak values,the shear strength of the embedded structure was increased by adjusting the position of the fine particles and coarse particles in the shearing process;Before the peak,the skeleton dense structure,firstly with fine particles and coarse particles occur at the same time to adjust the position of the formation of strong chain more.then the force chain structure is stable,the fine particle position adjustment to increase the strength of the strong force chain to improve shear strength;Before the peak of the skeleton loose structure,the number of the strong chain is increased to a certain number through the adjustment of the position of the coarse particles,and then the adjustment of the position of the coarse particles makes the strong chain more stronger,but the number of changes is small.