Research on Particle Flow Simulation for Excavation Face Instability of Slurry Shield

Aiming at excavation face stability and ground surface settlement for large-diameter slurry shield driving in sand gravel stratum in Beijing, particle flow code PFC2D was conducted to examine the micro-parameters of particle flow model for sandy cobble ground. Moreover, the friction coefficient and contact modulus of soil particle, the thickness and strength of mud membrane, were used for analyzing and evaluating the effect of tunnel face. Results show that: the friction coefficient and contact modulus of soil particle as well as the thickness and strength of mud membrane have significant influence on the stability of excavation face. The smaller the friction coefficient and contact modulus of soil particle are, the more serious failure of the excavation face is and the larger the boundary of ground collapse becomes, and the deeper ground settlement trough is. When the friction coefficient of soil particle reaches to 2.4 and its contact modulus reaches to 12×107 N·m-1, the excavation face tends towards stabilization. Moreover, the curve of settlement trough is flat and the vertical displacement of ground surface is smaller. The smaller the thickness and strength of mud membrane are, the more obvious the extrusion of the excavation face is, which can easily cause a wide range of ground deformation, and directly leading to ground collapse. When the thickness of mud membrane reaches to 20 mm and its strength reaches to 1 400 N·m-1, the stability of excavation face can be ensured during construction. © 2017, Editorial Department of China Railway Science. All right reserved.