Study on seepage force and stability of shallow shield tunnel excavation face at the varied water level

In order to analyze the stability of the shallow buried shield excavation face under the influence of seepage force in the permeable strata in riverside area, combined with the typical section of the shield tunnel of the pipe gallery along the east river road in Anqing City, the three-dimensional fluid-solid coupling numerical model of the shallow buried shield was established, the influence of water level change and soil mechanical properties on the stability of the excavation face and the change pattern of seepage force were analyzed, the instability form of the excavation face with the permeability of the shallow buried shield was clarified, and the mathematical model of the round platform-arc rotation was established, which was different from the traditional failure model. Compared with the existing research, the feasibility of the method was verified, and the influence of water level, soil mass mechanics and shield tunneling parameters on the limit support pressure were analyzed. The results show that the height of the failure zone significant decreases with the increase of cohesion and internal friction angle, while the height and length of the failure zone increase with the increase of water level. The seepage force on the excavation surface increases with the increase of the distance from the vault, and the seepage force changes linearly with the water level, and the average seepage force change rate with the water level to 2.75 kN·m-3. Combined with the mechanical properties of the soil layer in front of excavation, the limit support pressure changes rate with the water level of 5.11-5.75 kPa, which is consistent with the measured soil silo pressure change rate of 6.38 kPa and the control of the soil silo pressure above 80 kPa can effectively keep the stability of the excavation face. © 2024 Central South University. All rights reserved.