黄土地区浅埋暗挖地铁连拱隧道合理错距研究

Research on the Reasonable Staggered Distance of Tunnel in Shallow Excavated Metro Arch Tunnel in the Loess Area

研究目的:以西安地铁5号线雁鸣湖停车场段暗挖双连拱隧道工程为背景,采用有限元分析方法对主洞开挖过程进行模拟,研究开挖错距(0 m、15 m、30 m、60 m)对地表变形、拱顶沉降、拱腰净空收敛及拱顶应力的影响规律,并结合现场监测数据对黄土地区浅埋暗挖地铁双连拱隧道合理错距进行研究分析。研究结论:(1)四种方案下地表沉降值最大相差仅0.5 mm且均满足规范要求,横向地表影响范围大概在连拱隧道中线两侧约3倍隧道跨径内;(2)拱顶沉降和拱顶应力变化主要集中在隧道上台阶施工阶段,当错距超过30 m后,拱顶最终沉降值及应力值基本不受错距变化的影响;(3)错步方案下先行洞拱腰净空收敛值均大于后行洞,且随着错距的增加,后行洞开挖对先行洞拱腰净空收敛的影响逐渐减小;同步开挖过程中不存在偏压问题,且拱腰净空收敛值比其他三种方案小;(4)同步开挖方案与其他错距方案相比较,未引起过大地表沉降及拱顶沉降,且拱腰净空收敛相对较小,综合考虑安全性、经济效益和施工效率等因素,在黄土地区类似工程中建议优先采用两主洞同步开挖方案;(5)本研究可为黄土地区城市地铁双连拱隧道主洞开挖施工方案优化及力学行为研究提供有益参考。

Research purposes: This paper relied on shallow excavated double-arch tunnel excavation project of the Yanming Lake parking lot section of the Xi’an Metro Line 5. The finite element analysis method was used to simulate the excavation of the main tunnels. The influences of different staggered distances( 0 m,15 m,30 m,and 60 m) on surface settlement,arch waist horizontal convergence,vault settlement and stress were studied. And combined with on-site monitoring data,the reasonable staggered distance of shallow buried underground double-arch tunnel in loess area was studied and analyzed.Research conclusions:( 1) The maximum difference in surface settlement value is only 0. 5 mm and all meet the requirements of the specification under the four schemes. The range of lateral surface influence is about 3 times of the span of the tunnel on both sides of the central-line of the multi-arch tunnel.( 2) The arch settlement and arch stress changes are mainly generated in the construction stage of the upper bench of the tunnel. The final settlement and stress values of the arch are not affected by the change of staggered distance when it exceeds 30 m.( 3) The clearance convergence value of the hance of the first hole is larger than that of the following hole under the staggered step schemes,and the influence of the excavation of the following hole on the clearance convergence of the hance of the first hole decreases with the increase of the staggered distance. In the process of synchronous excavation,there is no bias problem,and the arch waist clearance convergence value is smaller than the other three schemes.( 4) The synchronous excavation scheme does not cause excessive surface subsidence and vault subsidence,and the clearance convergence of arch waist is relatively small,compared with other schemes. Considering the factors of safety,economic benefit and construction efficiency,the synchronous excavation scheme is suggested priority in similar projects in loess area.( 5) The research can provide a useful reference for the optimization of the main tunnel excavation scheme and the research on the mechanical behavior of the double-arch tunnel in the loess region.