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

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