硬岩地层地铁暗挖车站施工过程力学分析

Construction Process Mechanical Analysis of Subway Underground Excavation Station in Hard Rock Stratum

地铁暗挖车站因其埋深浅、开挖尺寸大,隧道围岩应力演化剧烈且复杂,塌方事故风险大,隧道支护设计面临极大挑战。为精细化模拟地铁暗挖车站分部开挖及初期支护全过程,以青岛地铁6号线海港路站为对象,建立三维数值模型,结合现场监测数据,研究硬岩地层暗挖大跨隧道施工过程力学特征。结果表明:拱部上导洞开挖造成围岩强度储备显著降低,引起拱顶及地表沉降量占最终值的54%和56%,左、右导洞开挖对应的拱顶围岩应力变化较小,引起拱顶沉降分别占最终值的30%和13%,直墙部等后续施工影响更小,从总体过程来看上导洞开挖对隧道沉降控制最为关键。全部贯通后,拱顶围岩强度储备值高于其他部位,边墙围岩强度储备值接近极限状态,从隧道各部位围岩强度储备角度上看,边墙最为关键需支护。总体上,地铁暗挖车站虽跨度大、埋深浅,但由于硬岩地层围岩强度高而几乎没有产生塑性区,锚喷格栅初期支护即可使隧道达到较高的稳定状态。

Underground excavation subway station because of its size, buried depth, excavation tunnel surrounding rock stress evolution intense and complex, collapse accident risk big, the tunnel support design is faced with great challenge. Taking the hard rock underground excavation station of Haigang Road Station of Qingdao Metro Line 6 as the object, a three-dimensional numerical model was established to simulate the whole process of divisional excavation and initial support. Combined with the field monitoring data, the mechanical characteristics of the construction process of long-span tunnel in hard rock stratum were studied.The results show as follows. The excavation of the upper pilot tunnel in the arch results in a significant reduction in the strength reserve of the surrounding rock, resulting in 54% and 56% of the final value of the vault and surface settlement. The stress change of the surrounding rock of the arch crown corresponding to the excavation of the left and right pilot tunnels is small, resulting in 30% and 13% of the final value respectively. The subsequent construction of the straight wall has less impact. From the overall process, the pilot tunnel excavation is the most critical to the control of the tunnel settlement. After all the tunnels are connected, the strength reserve value of surrounding rock at the vault is higher than that at other parts, and the strength reserve value of surrounding rock at the side wall is close to the limit state. From the perspective of strength reserve of surrounding rock at each part of the tunnel, the side wall is the most critical and needs support. In general, although the subway underground excavation station has a large span and shallow buried depth, there is almost no plastic zone due to the high strength of surrounding rock in hard rock stratum. The initial support of bolt shotcrete grid can make the tunnel reach a high stable state.