Study of the Formation and Supporting Principle of Filter Cake in Slurry Shield Tunneling by Particle Flow Code

摘要

The formation process of filter cake in slurry shield tunneling was simulated by particle flow code in 3 dimensions (PFC_3D), and the supporting principle of filter cake for maintaining the stability of excavation face is discussed. The simulation results show that the formation of filter cake is mainly depended on the particle size distribution of slurry and the pore sizes of stratum. The well graded slurry particles can form more compact filter cake on the excavation face than the poorly graded slurry particles. The more compact filter cake can be formed on the surface of stratum with smaller pore sizes. Moreover, the thickness of filter cake decreases with the increase of pressure difference between slurry and stratum. The supporting principle of filter cake is that the sum of driving force applied by the water to the filter cake, which containing the force applied to filter cake particles by the pressure gradient and the interaction force between filter cake particles and water, provide the horizontal effective stress to balance the horizontal earth pressure in the ground. Therefore, the more compact the formed filter cake, the larger the induced pressure gradient in the filter cake, and then the bigger the resulted horizontal effective stress in the stratum for maintaining the stability of excavation face.