Pore Water Pressure Responses in Sand Stratum during Shield Tunnelling: A Case Study

When shield tunnelling is in a water-rich sand stratum with poor bearing capacity, instability is easily generated, and even ground collapses may occur. The variation of pore water pressure in a water-rich sand stratum during shield tunnelling was analyzed based on a large-scale cross-river shield tunnel in China, which was also investigated by a three-dimensional fluid-solid coupling finite element model. The results show that the influence range of the pore water pressure in front of the excavation face is approximately 2.0 times the excavation diameter and 1.5 times on both sides of the shield. The tunnelling steps would cause obvious variation in the pore water pressure and lead to great disturbance to the surrounding fine sand stratum. The quality of filter cake and the set of support pressure imposes an important impact on the nonlinear variation in the pore pressure, which could cause great disturbance to the stratum. To ensure the safety of the subsequent tunnelling in the fine sand layer, effective treatment should be taken.