Analytical solution for seepage field and spewing discrimination during propulsion process of earth pressure balance shield

Considering the excess pore water pressure generated by the additional thrust on the shield front during the propulsion process, the shield spewing problem is analyzed by the analytical method. The seepage field in soil chamber is divided into two regions, the superposition principle and the separation variable method are used to obtain the explicit level solution for the water head in the soil chamber, the flow field inside the screw conveyor is regarded as one-dimensional seepage, and the analytical solution for the shield seepage field is determined by using the continuity condition of the intersection between the soil chamber and the screw conveyor. The correctness of the solution is verified through the numerical simulation results, and the parameters are analyzed. The parameter analysis shows that the ratio of shield thrust fluctuation frequency to soil consolidation coefficient in the normal tunneling state is about 0.1~10 m^-2, which corresponds to the permeability coefficient 10^-3~10^-5 cm/s, when the ratio is greater than 20 m^-2, the influences of the excess pore water pressure can be ignored, and when the ratio is less than 0.01 m^-2, the water pressure distribution approximates in the steady-state seepage state, but for the ratio near 1 m^-2, the excess pore water pressure will have a significant impact. Combined with the existing spewing researches, the critical permeability coefficient of a typical shield in different ratios thrust fluctuation frequency to soil consolidation coefficient is given. By comparing the shield spewing examples, the spewing discrimination of the analytical solution is proved to be effective.