Analysis And Control Measures Of Shield Surface Subsidence Based On Stratum Loss Theory

Sandy stratum is a typical unstable stratum,the clearance of the sand is huge,and the cohesive force is small,the stratum response sensitivity,it is very easy to destroy the original stable state of the strata during the tunneling of the shield,hence the disturbance of soil is large,resulting in a greater stratum loss.In this paper,indoor test,numerical simulation and field monitoring were combined to study the effects of the ground loss ratio,the depth of the shield,the continuity of the ground loss and the change of the groundwater level on the vertical and lateral surface subsidence.Based on Lanzhou Metro project,this paper also put out the optimization tunneling parameters for the controlling of surface subsidence.The main results are as follows.(1)In this paper,the causes of formation loss caused by shield tunneling were analyzed and summarized,meanwhile,the discrete element PFC was used to analyze the development process of strata loss caused by shield tunneling from the micro level in sandy strata,and the influence of the loss rate,the continuity and the depth of the tunnel on the surface subsidence were analyzed by using the granular flow method.(2)The 3D model of shield tunnel is established by using FLAC3D software,and dynamic simulation of shield tunneling was realized by changing parameters of the materials.In the calculation,different stratum loss were simulated by changing the gap parameter g,the influence of buried depth and ground loss ratio on the surface subsidence are also analyzed.(3)An indoor model test was carried out with the geometric similarity ratio of 1:20,stratum loss is simulated by the drainage of liquid bag.According to the stratum conditions of dry and wet sand,the effect of the ground loss ratio,the depth of the shield,the continuity of the ground loss and the change of the groundwater level on the vertical and lateral surface settlement are summarized.(4)This paper concluded the dynamic change law of the shield tunneling parameters and the mutual influence between the thrust,the torque,the driving speed,and the cutter speed based on the shield tunnel project of Lanzhou Metro Line 1 Yingmentan?Matan which is under the Yellow River.FLAC3D numerical simulation method was used to analyze the relationship between surface subsidence and tunneling parameters such as support pressure and grouting pressure during construction.Finally,the optimization tunneling parameters for the controlling of surface subsidence are presented.