Numerical Analysis Of Vertical Reinforced Sand In Direct Shear Tests Using Particle Flow Code

Geosynthetic encased sand columns is an efficient and economic method of foundation treatment, whose shear properties are researched rarely. Vertical reinforced sand direct shear tests are researched to understand the interface shear characteristics between bag body and pile soil and to provide further research on the shear characteristics of geosynthetic encased sand columns with vertical loads. This paper is to study reinforced sand direct shear tests in the microscopic particle level by PFC2D,revealing the microscopic phenomenon and mechanism. In this paper, work and research results are as follows:(1) The macro shear strength variations on the influence of mesoscopic parameters are fully analyzed from the following several aspects:particle grading, particle contact stiffness, particle contact stiffness and particle shape.(2) The granules of particle friction coefficient value is0.2-10, and the relationships between material peak angle of internal friction value and the particle friction coefficient are gained in the direct shear tests. The problem of particle rotation is discussed and the particle sliding and rolling failure mechanisms are provided and researched. The particle size effect is also discussed. Because of the inherent defect in PFC2D that circular particle is use to simulate the actual irregular sand, four methods to improve the stress ratio are put forward. The critical loading rate is also analyzed.(3) Numerical analysis is put on vertical reinforced sand direct shear tests. In the macroscopic circumstances, the changes of shear stress-displacement curve are observed due to the influence of reinforced layer, compactness, reinforcement material tensile modulus and reinforcement material friction coefficient. In the microscopic circumstances, mechanical properties in the shear process are gained and discussed in the aspects of particle contact state, particle distribution state, particle motion state and principal stress deflection. The influence of reinforcement is analyzed relatively from the macro and micro aspects.The innovation point lies in using the particle flow program PFC2D to do some analysis for sand direct shear tests. A layer of vertical reinforcement and two layers of vertical reinforcement are separately carried on the concrete analysis. Emphatically, the changes of the microscopic mechanism are discussed in detail in the process of reinforced soil shear from the particle level.