穿越紧邻隧道时盾构开挖面稳定性分析

当盾构近距离穿越邻近隧道时,由于存在既有隧道的刚度约束,隧道周围土体的破坏模式会受到既有隧道影响。考虑盾构近距离穿越紧邻已有隧道的特殊施工形式,构建三维弹塑性有限元计算模型,分析盾构处于不同位置时其开挖面失稳破坏形态、开挖面支护压力与盾构掘进位移之间的关系以及隧道上方地表沉降规律;基于极限平衡法,推导盾构近距离穿越紧邻隧道时开挖面极限支护压力变化模式,并对相关参数的敏感性进行验证讨论。研究结果表明:既有隧道的存在使得破坏区域受到抑制,沿开挖方向两滑动面不对称,靠近既有隧道的滑动面张开角比另一滑动面张开角小;随着楔形体倾斜角增大,相同内摩擦角条件下的开挖面支护压力不断增大,同时由于盾构掘进产生的土拱效应和盾构开挖面上方既有隧道的刚度约束,随着内摩擦角的不断增大,开挖面支护压力呈先增大后逐渐减小的抛物线形变化;相同参数条件下,盾构在黏性土层中掘进时,由于黏性土层中产生的土拱效应较弱,所需提供开挖面稳定的支护压力略大,开挖面支护压力较盾构在砂性土层中掘进时略大,随着埋深比的增加,维持盾构开挖面稳定的极限支护压力逐渐增大,且随着内摩擦角的增大,开挖面极限支护压力相应增大。研究成果可为类似盾构隧道工程建设提供一定的理论参考。

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.