隧道密贴下穿既有地铁车站沉降控制研究

Study on Settlement Control of Tunnel Closely Passing through Existing Metro Station

本文以北京地区冲洪积地层条件下,地铁机场西延线隧道下穿既有5号线北新桥站工程为依托,对地铁隧道采用洞桩法施工密贴下穿既有地铁车站,引起地表及既有地铁车站的沉降规律进行研究,并提出沉降控制方案。结果表明:下穿施工工程中,地表和既有车站底板沉降主要产生在浇筑二衬扣拱阶段。地表沉降呈现出以既有车站两侧的下穿隧道上方为中心沉降量最大,向周边沉降量逐渐减小的特点。车站底板形成与车站中线平行的沉降带,中间条带沉降量最大,两侧随距离增加逐渐减小。本文对洞桩法施工工序提出优化方案,改变浇筑二衬扣拱前,开挖中导洞的距离,模拟结果表明:中导洞开挖隧道总长的1/4后浇筑相应段的二衬扣拱,相较于中导洞开挖贯通后浇筑二衬扣拱,地表最大沉降量减少25%,既有车站底板降量减少7%。

The paper studied the subsidence law of the ground surface and existing metro stations by a crossing project which is the subway tunnel of Airport West Extension line beneath existing Beixinqiao station of the No. 5 line by cave pile method in the Beijing alluvial strata area. The results show that the settlement of the ground surface and the floor of the existing station mainly occurs in the stage of supporting arch of the second lining arch. Ground subsidence is characterized by the largest settlement centered on the top of the tunnel on both sides of the existing station and decreases gradually towards the surrounding area. The settlement zone parallel to the middle line of the station is formed on the bottom of the station and the subsidence of the middle strip is the largest. The two sides gradually decrease with the increase of distance. In this paper,the optimum scheme for the construction procedure of cave pile method was put forward which changes the distance of the pilot tunnel in the excavation before the pouring of the second lining buckle arch. The simulation results show that compared with the construction of the secondary lining arch after the middle guide tunnel construction,the maximum settlement of the ground surface of the construction of the secondary lining arch after excavation of 1/4 of the total length of the middle guide tunnel is reduced by 25% and the reduction of the existing station floor of that is reduced by 7%.