The Meso-simulations Of Triaxial Tests And Microstructure Study Of The Cohesive Soil

The cohesive soils are weakly bonded sediments formed by weathering effect of rocks and transferred in different ways in the natural environment. The granular units have great influence on its macroscopic mechanical properties. In this paper, conventional triaxial tests of clay are simulated by the three-dimensional ideal discrete element particle flow method. Also, the effect of stress-strain relationship, the law of body strain development and the contact strength, stiffness,friction coefficient and other microscopic parameter changes on macro-mechanical properties are investigated in this study. We have conducted a series of directional shear tests and pure principal stress cycle under different principal stress directions through Hollow Cylinder Apparatus (HCA),the Scanning Electron Microscopy (SEM) and Particles and Cracks Analysis System (PCAS). The microstructures of the samples under different principal stress directions on the same microscopic observation surface and the same samples were analyzed. The main conclusions are drawn as follows:1. The meso-simulations of the cohesive soil triaxial tests are carried out through three-dimensional ideal discrete particle flow method (PFC3D) to obtain the stress-strain curve consistent with the change trend of the indoor soil test. However, the intensity of the mesoscopic numerical test is slightly lower caused by the particle shape being simple. In the mesoscopic simulation, the initial porosity of the numerical sample has a considerable effect on the bulk strain.The increase of the friction coefficient between the particles will cause the peak intensity and the residual strength to increase obviously, and the strain softening will be developed. The increase of the bulk elastic modulus and the dilatancy characteristic of the material increase significantly,and the increase of the particle stiffness ratio mainly leads to the increase of the Poisson's ratio and the shear strength. The increase of the normal bond strength will significantly improve the peak strength and residual strength of the material, which also have a certain impact on the initial linear elastic modulus and shear shrinkage shear.2. In fixed principal stress direction tests, the orientation of the particles on the horizontal plane (RO) will be enhanced continuously with the increase of large principal stress angle a, the orientation of the large principal stress direction a will be increased, while the orientation of the horizontal plane (RO) will be improved and the ZO and ZR surface of it experiment a upward and downward trend. The arrangement of the particles is the best when a is 60 °, In pure principal stress rotation tests, the increase of the rotation angle a of the principal stress axis is mainly affected by the size, arrangement and shape of the particles on the ZO surface and the RO surface,and the influence on the RO surface may be neglected.3. The effect of the change of the principal stress direction on the microstructure of the particles reveals that the compressibility of the soil is the largest in the directional shear when a is 50 °, the law that the angle between macro-shear zone and large principal stress direction remains unchanged when the specimen is broken and other macro-micro-mechanism of action.