Stability Analysis of Excavation Face During Shield Passing Through Adjacent Tunnels

When shield tunnels pass through adjacent tunnels at close distance, the failure modes of soil around tunnels are affected by the rigidity constraints of existing tunnels. A three-dimensional elastic-plastic finite element model was used to analyze the failure modes of the shield excavation surface. The relationship supports that the pressure of the excavation surface and the displacement of shield excavation, ground settlement, and law are higher than those of the tunnels. On the basis of the balance method, the variation model of the ultimate abutment pressure of the shield tunneling face was deduced when shield tunneling approached the tunnel, and the sensitivity of relevant parameters was verified and discussed. The results show that the existing tunnel restrains the damage area, the asymmetrical sliding surfaces along the excavation direction, and the opening angle of the sliding surface near the existing tunnel is smaller than that of the other sliding surface. With the increase of the inclination angle of the wedge, the supporting pressure of the excavation face increases continuously at the same internal friction angle. At the same time, owing to the soil arch effect caused by shield tunneling and the rigidity constraint of the existing tunnel above the shield excavation face, with the increase of the internal friction angle, the supporting pressure of the excavation face first increased and then decreased gradually. Under the same parameters, when the weak soil arch affects shield tunneling in the clay layer, the support pressure needed to provide stable excavation face is slightly larger, and the support pressure of the excavation face is slightly larger than that of shield tunneling in sandy soil layer. With the increase of burial depth ratio, the role of maintaining the stability of the shield excavation face is maintained. The limit support pressure gradually increased, and with the increase of the internal friction angle, the limit support pressure of the excavation face increased correspondingly. The research results provide a theoretical reference for similar shield tunnel construction. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.