Study On Construction Mechanical Effect Of The Interchange Pile Foundation Adjacent To Metro Tunnel

The problem of building foundation adjacent to tunnel is always the key point of the close-spaced construction in tunnelling.Especially for the mountain cities such as Chongqing,due to the constraints of terrain conditions,surrounding environment,subway line selection,and so on,the cases of building foundation adjacent to tunnel increase.If the bearing layer of the construction foundation is located just within the disturbance range of the new tunnel,the additional response to the foundation caused by the ground deformation will directly affect the safety of the superstructure.This paper mainly deals with the series of problems in pile foundation of overpass adjacent to buried tunnel of subway interval.The regularities of distribution of additional deformation and additional internal force of pile foundation which caused by tunnel excavation.Taking pile,tunnel and strata as a whole sample,the influence of existing pile foundation on tunnel supporting structure and surrounding stratum is analyzed.Combined with the example of the LiuJiaYuanZi Overpass adjacent to Min'an Avenue Station to Chongqing North Railway Station metro tunnel of line 4 in Chongqing rail transit,the additional response of the pile foundation under the construction conditions and the internal force change of the tunnel supporting structure are used to verify the theoretical results.Finally,the safety control measures are worked out for the engineering example,so as to ensure the safety of the superstructure and provide reference for similar engineering design and construction.The contents and conclusions of this paper have the following points:(1)The displacement of two kinds of stratum(single stratum and composite strata)under the tunnel excavation is studied by image method,and the calculation model which is closest to the numerical simulation results is selected as the theoretical basis for calculating the ground displacement of the additional response of single pile.The two stage method is used to calculate the additional internal force and displacement of the single pile under the tunnel excavation,and compared with the numerical simulation results,it is found that the theoretical solution has the same change rule with the numerical solution.A three-dimensional numerical model of stratum without piles is established to get the longitudinal influence range of the single strata and the composite stratum under tunnel excavation.(2)Through the analysis of the numerical simulation results of the single pile in different horizontal distance and the different vertical distance with the pile under the tunnel excavation,the scope of influence of tunnel excavation on adjacent pile foundation in two kinds of stratum is obtained.The calculation results of single pile are compared with the group piles to get the similarities and differences.(3)Using the single-factor analysis,and studying the internal force distribution of tunnel supporting structure under different length of piles and relative distance between piles and tunnel,the safety distance of existing pile foundation in two stratum to the supporting structure of new tunnel is obtained.It compares the internal force distribution of tunnel supporting structure in single pile and group piles.(4)Establishing a three-dimensional numerical model,and increasing the pile-soil interface unit,the additional reaction of pile foundation and the internal force distribution of tunnel supporting structure which under the condition of three dimensional construction are obtained.Comparison with the analysis results of single pile,it is found that there is a lot in common.Chosing the 2-1 pile as the research object of the variation law of pile foundation internal force during tunnel construction,the influence scope of tunnel construction on the excavation direction of pile foundation is obtained.It is consistent with the conclusion of longitudinal influence range of tunnel excavation in stratum without piles.(5)On the basis of analyzing the control standards of bridge deformation in different codes and related works,the risk control standard of adjacent construction based on displacement and pile foundation strength is proposed.Finally,the safety control measures of pile foundation based on adjacent construction are put forward in this paper,and the effectiveness of safety control measures is verified by numerical simulation.