Study On The Optimization Of The Construction Scheme Of Breaking The Retaining Pile In The Connection Section Of Foundation Pit And Tunnel

With the rapid development of urban construction and the large increase of urban population,the urban surface public transport has gradually become saturated,and the problem of traffic congestion is becoming increasingly prominent in the city.The daily life of urban residents and the sustainable development of urban economy are also seriously affected.In countries where conditions permit,the development of underground traffic has been proved to be an effective measure to alleviate urban traffic jams,and tunnels are the most typical form of underground traffic.Because the construction of the tunnel is closely related to its environmental conditions,sometimes the tunnel can not be constructed by full open excavation or full cover excavation,but the form of full concealed excavation construction has high cost,long construction period and high construction risk.Therefore,the combination of open and concealed excavation has been widely used in many projects,and achieved good results.When the tunnel is built by the combination of open excavation and concealed excavation,the open excavation section often uses the way of backfilling after the deep foundation pit,while the construction of deep foundation pit often uses the support form of retaining pile and internal support.When the foundation pit is completed,the retaining pile may invade the tunnel construction boundary,so it is necessary to break the retaining pile which invades the boundary.This paper analyzes the broken pile construction of the foundation pit and its connecting section The optimization of work plan is studied.Based on the first phase project of North Avenue of Guanyinqiao business district in Chongqing,this paper studies the construction method of the retaining pile breaking in the foundation pit and its tunnel connection section,establishes a three-dimensional model with FLAC3 D 6.0 software,simulates the construction process of the retaining pile breaking in the foundation pit and its tunnel connection section,and achieves the following results:(1)According to displacement analysis,safety factor analysis of support structure,axial force analysis of retaining pile shaft and site construction conditions,it can be concluded that the method of first breaking retaining pile and then tunneling from the foundation pit is more suitable and safer for site construction conditions.(2)According to the analysis of the safety factor of the secondary lining in the tunnel section,it can be concluded that the method of first breaking the retaining pile and then driving the tunnel from the foundation pit is only suitable for the better surrounding rock above V level.If the surrounding rock condition is too poor,the construction method should be further evaluated and demonstrated.(3)According to the analysis of the change of the axial force of the pile body and the introduction of the reference quantity,it can be concluded that the order of breaking the retaining piles at the middle part and then at both sides should be selected.(4)According to the field situation and the field monitoring data,it can be concluded that the new technology of two knife method has better safety.