Experimental Test Study On The Influence Of Subway Crossing On The Pile Group Foundation Of Existing Bridges

With the increasing number of subway lines in large cities,the influences of both building foundation and underground pipeline on subway construction have been unavoidable in the construction of subway engineering.At present,the research of subway tunnel crossing through the existing structure is mostly the influence of the new subway tunnel construction on the safety operation of the existing subway tunnel.The research methods are mostly field monitoring,empirical statistics,and numerical simulation.The research on the pile foundation of the subway tunnel crossing through the existing buildings is still to be carried out.This paper relies on the design scheme of pile foundation underpinning of Yuergou Bridge of Line 1 of Lanzhou Rail Transit Line.The influence of subway crossing on the bearing behavior of existing bridge group pile foundation is studied through indoor model test.The conclusions are as follows:(1)In this paper,a new type of model pile is put forward and its application effect is evaluated by the model test of the ultimate bearing capacity of single pile.The test results show that the new model pile made by the new technology has good effect and can be popularized in the same type test.(2)As the subway crossing through the pile group foundation model test of existing bridges,the foundation settlement caused by the excavation of the simulated tunnel is greater than the foundation settlement caused by the cutting pile process;the axial force at the top of the truncated pile foundation pile is reduced by 55%~65% after the the truncated pile;and the greater the distance from the truncated pile foundation,the smaller the change of the axial force at the top of the truncated pile.(3)The axial force of each pile body abruptly changes when truncated piles and excavated tunnels.The position adjacent to the truncated pile foundation and the axial force of the pile adjacent to the subway tunnel vary greatly.The frictional resistance of each pile body is roughly a triangle distribution.The low platform has a certain degree of weakening of the pile side friction resistance of the pile below it.After the existing piles affecting the subway tunnel excavation are cut off,the loads shared by the top of each pile are increased.The part of the load is mainly borne by the pile side frictional resistance generated on the body half of each pile.(4)After the truncation of the piles affecting the subway tunnel excavation,the share of the upper load on the platform was slightly changed from the previous 30.9% to 35.93%.After the piles were cutted and the tunnel was built,the share of the upper load on the platform remain stable,and about accounting for approximately 35% of the upper load.(5)The test results show that there is room for further optimization in group pile arrangement adopted in pile group tests.The technology of the new model pile put forward in this paper has good effect and can be popularized.In this paper,through the model test of the subway crossing through the existing bridge pile group foundation,the truncation of the pile foundation which hinders the tunneling of the subway tunnel is treated and the process of the tunneling of the subway tunnel is simulated.The load of the upper piles and the loads of the piles at the top of each pile are tested at each stage of the experiment.The transmission situation and the ratio of the upper platform to share the upper load were studied.The test results have certain reference value for similar projects.