Analytical study on the seepage field of EPBS and preliminary discrimination of spewing

Abstract

Considering the two-dimensional seepage effect of a soil chamber, the spewing problem of an earth pressure balance shield (EPBS) is analysed by an analytical method. In this paper, an explicit analytical solution of the two-dimensional shield seepage field considering the water level distribution at the cutter surface is derived by using the separation of variables method and the superposition principle, and the unknowns in the analytical solution are solved by constructing a non-homogeneous system of equations. The correctness of the solution is verified by using the experimental and numerical simulation results, and a parameter analysis was conducted to investigate the effect of shield geometry and water head at the center of the cutter surface. The results show that water head on the cutter surface, screw conveyor angle, screw conveyor length and screw conveyor in the water flow and water pressure with an approximate linear relationship, reducing the screw conveyor diameter is most conducive to prevent spewing. On the basis of previous studies, the analytical solution can calculate the critical permeability coefficient for the occurrence of a spewing, and use the undisturbed soil or predicted permeability coefficient to preliminarily discriminate whether a spewing will occur. By comparing with the shield spewing example and with the shield one-dimensional analytical solution, it is proven that spewing discrimination based on this analytical solution is effective and more accurate. Since the analytical solution considers the water level distribution on the cutter surface, it can be used to discriminate the spewing of shields of any size.