Mesoscopic Characteristics And Macroscopic Application Research Of Sandy Pebble Soil Based On Discrete Element Method

In this paper,laboratory test and the Particle Flow Code software are combined to research the microscopic characteristics and the macro application of sandy pebble soil.The main contributions are as follows:(1)Research the particles shape,the connection and contact,the force-chain network of sandy pebble soil by means of particle modeling and numerical simulation.The particle shape has influenced on the porosity,the coordination and the contact force of soil,so that the granular system has different stability and accumulation performance.In the particle contact type,contacts of two points is the most easily broken,and contacts of two surfaces is the most stable.Moreover,in the particle system,there are tension-pressure force,bend torsion and shear force.The angle of geometrical contact can reflect the microscopic contact state of particles.The distribution frequency of the geometrical contact angle of sandy pebble soil changes less than the spherical particles after the load application,so the stability of sandy pebble soil is better.The connection mode of force chain can be summarized as linear connection,branched connection and annular connection.The length of force chain is inversely proportional to the contact force between particles.(2)Laboratory stacking test and numerical simulation of sandy pebble soil were experimented.Particle accumulation test was experimented under conditions of different fine content,different grading and different initial porosity.The natural angle of repose formed after stacking was measured to judge the stacking performance of sandy pebble soil under different parameters.Under the condition of different fine content,different gradation and different friction coefficient,the inclined plate pile-up test was carried out.The fine content,the gradation,the initial porosity and the friction coefficient of the gravel soil with the best stacking properties were determined.(3)Experimenting with tunnel excavation indoor and contribute a box model with full of sandy pebble soil.On the basis of suitable span,we set up three cases with different fine contents,different gradations and different friction coefficients then observed the settlement and collapse of the arch and surrounding soil during the excavation.In the numerical simulation experiment,we monitor the changes ofvertical soil pressure,coordination,unbalanced force and displacement in different location and come to the most stable conclusion.All that can provide theoretical basis for the quality of soil.(4)When using PFC software to discuss the effects of different micro parameters,we changed the values of micro parameters and observed changes of the macroscopic system,then contact both them and fit their relationship curve.Finally,we researched the relationship between friction coefficient and cohesive force,the relationship between contact modulus and cohesion and so on.