Experimental and numerical study on slurry fracturing of shield tunnels in sandy stratum

A series of 2D model tests on slurry fracturing of shield tunnels in the sandy stratum with different cover depths were conducted to investigate the slurry fracturing mechanism, the displacements of the ground surface, and the earth pressure distribution in the stratum. According to the test results, the slurry fracturing mechanism is that the dense sandy stratum and the filter cake on its surface (the filter cake-sandy stratum) is formed due to the pressurized slurry penetrating into the sandy stratum around excavation space, and then the filter cake-sandy stratum is pushed by the slurry to tensile and shear failure. The fracture pressure increases linearly with the increase of the cover depth. The fracture initiates on the top edge of the cutter head and propagates up to the ground surface in acclivitous direction directly, or first in straight and then in acclivitous direction. Based on a self-developed finite element program for simulating slurry fracturing, the 2D numerical models were established referring to the model tests, the numerical results including the morphology of the fracture propagation which agreed with the test results, and the vertical and horizontal displacements in the stratum were obtained. The numerical results show that the vertical displacement mainly distributes in a triangle region bounded by the fracture surface above the cutter head, while the horizontal displacement mainly distributes in the excavation face. Copyright ©2020 Journal of Zhejiang University (Engineering Science). All rights reserved.