Analysis Of The Relevance Between Macro-micro Parameters For Clays Based On Particle Flow Code Simulation

Red clay is a kind of highly plastic clay with special engineering properties^[1].Red clay its used as an ideal natural roadbed and a good building material because of its good mechanical properties in engineering,but at the same time it will have certain safety risks due to its engineering characteristics such as cracks and regional differences.The red clay particle unit has a great influence on its macro-mechanical properties from a meso point of view.In this paper,the research object is the filler red clay in the Petro China Yunnan Petrochemical Anning Refinery plant area,a numerical model is established based on the particle discrete element method?PFC3D?,and a number of plane unconsolidated undrained triaxial simulation tests are carried out for clays.The influences of different values of parameters?including friction coefficient,bonding strength,stiffness ratio,porosity and contact modulus?on macro mechanical properties are discussed.Through continuous inversion,the appropriate microscopic parameters are selected and the numerical simulation results are compared with the laboratory test results.Numerical model of PFC3D foundation soil based on meso parameter values has been set,simulation and analysis the surface settlement characteristics and the uneven settlement characteristics of foundation soil under preloading.The simulation results was consistent when we compared the numerical simulation results with the project example.The research results are as follows:1. A numerical model for triaxial shear test of red clay was established by using Particle Flow Code Three-dimension.The mesoscopic parameters,boundary conditions,contact types,etc.was selected conbined with the actual situation of indoor test,and the sensitivity of mesoscopic parameters was also analyzed,The stress-strain curve which is consistent with the trend of indoor geotechnical tests can be obtained,the Particle Flow Code three-dimensional numerical model of the triaxial shear test established in this paper is reasonable and effective.the research shows:The peak strength of the sameple will increase significantly with the increasing of confining pressure,friction coefficient and bonding strength;The axial strain corresponding to the peak strength will increase as the confining pressure,friction coefficient,bond strength,and stiffness ratio increase,while it reduced with the increasing of porosity;The increasing of friction coefficient and contact modulus will increase the initial tangent modulus of the specimen;The increasing of confining pressure,friction coefficient,and bonding strength will aggravate the stress softening phenomenon of the material,and the increase of porosity will weaken the stress softening phenomenon of the material;The increase of friction coefficient,bond strength,and stiffness ratio between particles will aggravate the amount of shear shrinkage and dilatancy of the sample;2. The shear strength indexes of red clay with different meso-parameters are calculated based on the stress-strain curve obtained from the triaxial shear numerical simulation test,and the correlation between the macro and meso-parameters is quantitatively analyzed,the research results show:The shear strength index of the soil is closely related to the meso-parameters;The internal friction angle of the clay will increase rapidly with the increas of the friction coefficient,and then stabilize;The increase of the porosity will make the internal friction angle decrease;The cohesion force is related to the friction coefficient,cohesion strength,and stiffness ratio,and the cohesion strength and the cohesion force are linearly related.3. A numerical model of the foundation soil was established based on themesoscopic parameters obtained from the shear triaxial numerical simulation test of red clay,the studies indicate:The numerical settlement results of the foundation's center surface are not only close to the data from the on-site monitoring results,but also have the same pattern,that is,the settlements show a sharp change in the initial stage,and then the settlement rate gradually weakens,finally,the settlement tends to be horizontal;The surface settlement increases with the stacking height;The settlement will gradually decrease with the depth of soil.