基坑开挖对下卧运营盾构隧道影响的数值模拟研究

上海外滩修建地下通道——外滩通道,通道南段采用明挖法施工,在延安东路路口与已建的延安东路隧道产生交叉跨越问题。外滩通道基坑坑底与延安东路南、北线隧道拱顶距离仅为7.1m与5.4m,基坑开挖必然使下卧运营隧道产生附加变形以及附加内力。为了研究外滩通道开挖对下卧延安东路隧道的影响,以及评价不同隧道保护措施的效果,通过三维有限元软件PLAXIS-GiD进行四组模拟,包括无隧道保护措施的工况、采取土体加固措施的工况、基坑开挖过程中在坑底进行堆载的工况以及同时进行土体加固和堆载的工况。实际工程中同时采用土体加固和堆载这两种措施来保护隧道,现场监测数据与对应的数值模拟结果具有较好的一致性。分析表明:基坑开挖将对下卧隧道产生很大的影响,且影响范围较大,约为6倍基坑宽度,施工中采取合理的隧道保护措施是十分必要的。

Numerical analysis of the influence of deep excavation on underneath existing road tunnel

An underground passage is built in the Bund,Shanghai.North part of the passage is constructed by shield and the south part by cut and cover method.In the south part,the passage passes above an existing tunnel,the East Yan’an Road Tunnel.The distance between the excavation bottom and the crown of the northbound tunnel is only 5.4m,and 7.1m for the crown of the southbound tunnel.The existing tunnel will inevitably undergo additional displacements and carry additional loads due to the excavation above.To investigate the influence of the construction of the Bund Passage on the East Yan’an Road Tunnel,numerical analysis is performed using the finite element code PLAXIS-GiD.The effectiveness of two protective measures,soil improvement and surcharge by heap loading,are evaluated.Good agreement is achieved between the results of numerical analysis and on-site monitoring.The results indicate that the deep excavation may significantly affect the underlying tunnel in a lateral range of about 60m and appropriate measures should be taken to protect the tunnel.