深圳地铁近接隧道暗挖施工地表沉降控制

Study on Control of Ground Surface Settlement:Case Study on Adjacent Tunnel Tubes of Shenzhen Metro

为研究变净距近接隧道暗挖施工中开挖工序对地表沉降的影响,以期得到最优开挖工序,以深圳地铁近接隧道施工为工程背景,运用理论分析、FLAC3D数值模拟和现场实测数据反馈等多种手段,对比了4种不同开挖工序引起的地表沉降,并对围岩支护后隧道施工在纵横方向上的地表沉降规律进行了研究。得到:1)若先行隧道开挖采用上下台阶法,后行隧道采用CRD法,那么后行隧道采用上下断面法开挖优于左右断面法,且先开挖靠近先行隧道的部分要优于先开挖远离先行隧道的部分;2)随着近接隧道净距的减小,开挖工序对地表沉降的影响减弱;3)加固圈对抑制变净距隧道的不均匀沉降有着明显的效果;4)采用上下断面法开挖的近接隧道,上半部分开挖是控制地表沉降的关键,最大地表沉降值发生在靠近后行大跨度隧道中轴线一侧。

FLAC3D model is established and numerical analysis is made on a pair of adjacent tunnel tubes of Shenzhen Metro, so as to study the ground surface settlement of adjacent tunnel tubes caused by different excavation sequences and, in the end, to obtain the optimal excavation sequence. In the study, advanced supporting of the surrounding rock is simulated by equivalent reinforcement rings. The following conclusions are drawn by study on the ground surface settlement pattern in the vertical and horizontal directions caused by different excavation sequences, as well as on basis of the theory and field monitoring data ： 1 ） If the preceding tunnel tube is excavated by top heading and bench method and the following tunnel tube is excavated by CRD method, it is better that the following tunnel tube should be excavated in upper-lower sequence and that the part close to the preceding tunnel tube should be excavated first; 2） The influence of the excavation sequence on the ground surface settlement reduces as the distance between the twin tunnel tubes de- creases; 3 ） The reinforcement ring has obvious effect in retraining the differential settlement of the adjacent tunnel tubes; 4） The top heading plays a key role in controlling the ground surface settlement, with the maximum ground sur- face settlement occurring at the position close to the centerline of the following large-span tunnel tube.