Research On Influence Of Shield Tunnel Construction On Adjacent Bridge Piles

With the continuous expansion of the urban rail transit network,new subway tunnels will inevitably be adjacent to the existing bridge pile foundations.Tunnel construction will adversely affect the normal use of adjacent bridges and even cause safety problems.Therefore,the research on the influence of shield tunnel construction on adjacent bridge piles and the control measures have important engineering application value for the safe construction during shield tunnel crossing the bridge.In this paper,by consulting relevant domestic and foreign literatures,first of all,from a theoretical perspective,the influence law and cause mechanism of ground deformation caused by shield construction are summarized and analyzed.Furthermore,the interaction between tunnel,stratum and bridge piles is discussed.The types of influence of tunnel construction on adjacent pile foundations are divided,and the risk classification of tunnel adjacent bridge pile projects is classified.Then based on the Beijing Metro Line 19 Xinfadi Station ~ Caoqiao Station shield tunnel under-pass Majialou Overpass of Beijing-Kaifeng Expressway,the FLAC 3D numerical calculation software was used to simulate the construction process of the shield tunnel adjacent to the bridge pile,and it was verified whether the remaining bearing capacity of the pile foundation can meet the bearing requirements.Finally,the control measures for the construction of the adjacent bridge piles of the shield tunnel are briefly summarized,and combined with engineering examples,the control measures such as ground grouting reinforcement for the shield crossing section are elaborated in detail.At the same time,the main monitoring schemes were determined,and the reasonableness of the control measures and monitoring schemes was verified in combination with the on-site monitoring results.The results show that:(1)the vertical deformation of the stratum(that is,the settlement of the pile body)is the main reason for the reduction of the bearing capacity of the pile foundation.According to the degree of influence of tunnel construction on adjacent bridge piles,the pile foundation types can be divided into 4 types: Arch pile,upper pile,side pile and non influence pile.The design should avoid the tunnel from passing directly below the pile foundation.(2)According to the numerical simulation results,the settlement of the bridge pile is related to the distance between the excavation surface and the bridge pile.Without reinforcement measures,the maximum settlement of the bridge pile is 4.63 mm,which exceeds the monitoring control value,and the maximum settlement occurs at the corner of the cap near the left-line tunnel.The calculated remaining bearing capacity of the pile foundation still meets the bearing requirements.(3)Combined with engineering examples,the reinforcement measures of combining "sleeve valve tube grouting on the ground" and "radial grouting inside the tunnel" for the stratum of the shield crossing are proposed.After the stratum reinforcement measures are taken,the maximum settlement of the bridge pile is 2.68 mm,which is about 42% less than that of the unreinforced case.The reinforcement effect is significant and the control value is met.(4)The on-site monitoring results are in good agreement with the data of the maximum settlement of bridge piles and the maximum settlement of ground surface obtained by numerical simulation.Numerical simulation methods can provide reference and guidance for the construction of shield bridges adjacent to the pile.