超小净距地铁三洞隧道群施工动态数值模拟

摘要

Research purposes: With the aim to study the construction behavior of triplet tunnels group with extremely small spacing, the construction progress was numerically simulated by finite differential software FLAC3D.Based on the numerical simulation, the construction behavior characteristics such as the ground surface, crown settlements, failure area distribution of surrounding soils and the influence on the as-built tunnels from subsequent construction are presented.The construction scheme is also evaluated according to the numerical simulation and then optimizing suggestions are proposed.Research conclusions:(1) During the excavation of two side tunnels, the ground settlement presents W-shape and the settlement centers are located above the central lines of the side tunnels.While the middle tunnel is excavated using CRD method, the ground settlement above the middle tunnel is much greater than the ground settlements above the side tunnels and the final ground settlement trough shows some skewness.(2) In the construction progress of triplet tunnels group with extremely small spacing, the failure area of surrounding soils has been continuous when the side tunnel construction is completed.Grouting reinforcement can effectively prevent the expansion of the failure area.(3) The influence on the primary support structures of constructed tunnels from subsequence construction is significantly greater at the entrance section with extremely small spacing.Especially the compressive stress increases greatly.(4) The numerical simulations results agreed with site monitoring data very well which proves the reliability of numerical simulation computation.(5) The research result can provide a reference for the design and construction control of similar projects.%研究目的:为研究超小净距三洞隧道群的施工性态,采用FLAC3D有限差分软件对其施工过程进行数值模拟计算,得到其地表位移、拱顶下沉、围岩破坏区分布以及后继施工对先建结构物的影响等施工动态特征数据,根据计算结果评价施工方案,并提出合理建议.研究结论:(1)两边洞隧道开挖时,地表沉降在横向呈"W"形,沉降中心位于两边洞中线上;采用CRD法开挖中洞隧道时,中洞隧道中线处地表沉降速度大于边洞中线处沉降速度;最终沉降槽表现出一定的偏态性;(2)超小净距三洞隧道群施工中,边洞施工完毕时围岩中就已形成连通的破坏区,注浆加固能有效阻止破坏区的扩展;(3)后施工隧道对先施工隧道初期支护结构在洞口小净距段影响较大,尤其是压应力增值较大;(4)数值模拟结果与现场实测数据吻合良好,印证了数值模拟计算的可靠性;(5)该研究成果可为类似工程的设计与施工提供参考.