Research On The Deformation Law And Construction Control Of Metro Shield Tunnel Through Urban Existing Viaduct

With the rapid development of urban rail transit construction,the new shield tunnels will underpass existing urban viaducts inevitably.Especially in the composite stratum,the difference between the strength of adjacent strata makes it difficult to control the earth pressure and the volume of excavated earth during the shield process.It may cause large deformations of surrounding strata,which threaten the structural safety and daily operation of urban viaducts.So it is necessary to study the deformation law when shield tunnels underpass urban viaducts in composite strata and its influence on safety of urban viaducts.And choosing reasonable technical measures and shield construction parameters during shield construction to ensure the safety of viaducts has become an important issue to be solved urgently.Firstly,this paper expounds the relevant research theories and methods of surface settlement and bridge deformation caused by shield construction.Then,based on a practical project of shield tunnel through a existing urban viaduct in Guangzhou,the Peck formula was used to predict the ground subsidence caused by the shield construction.Furthermore,the corresponding three-dimensional finite element model was established to study the deformation of the bridge in the process of construction.Finally,combined with the monitoring data of the project,a comparison with the theoretical prediction values and numerical results were analyzed deeply.The main research conclusion can be seen as follows:(1)Based on similar cases,structure types of viaducts and structure health monitoring data of existing viaducts,controlling values for deformation of viaducts can be determined.(2)The Peck formula is used to calculate the ground settlement induced by shield construction.Through theoretical calculation,and considered geological factors,it is helpful to grasp the safety risks in the construction process.Compared with the practical data,it is also helpful to verify the effectiveness of control measures in the construction process.(3)According to simulate the construction process of shield tunneling through urban bridges in composite strata by Midas software,and the numerical simulation is in good agreement with the measured data.It is conducive to making a prejudgment on the risk control of shield tunneling through bridges,and provides a reference for the construction of the same type of shield tunneling through urban bridges in composite strata.(4)Through the risk control of the whole process of shield construction and the effective control of the actual construction parameters,the ground settlement and the impact on the bridge structure are basically consistent with the preset parameters,and the purpose of ensuring the safety of the viaduct by shield tunneling construction is achieved.