Settlement Analysis And Control Research In Metro Shield Tunnel Tunneling Underneath Existing Railways

With the high-speed development of subway construction, there are more and more projects of subway tunneling under the railways. The subway construction will disturb the surrounding strata, resulting in the settlement and differential settlement of existing railway subgrade, which is not conducive to the safe operation of the railway. Therefore, the research of railway subgrade settlement deformation law during the subway construction and the control effect of stratum reinforcement measures to subgrade settlement are significant. In addition, the conventional numerical simulation method of shield construction seldom consider the frictional and shearing effect on surrounding soil during shield tunnel construction, which is one of the important features of the shield method different from the others. Therefore, how to considering the effect of shield friction on the ground deformation in the process of shield construction numerical simulating is a problem worthy of study.In this paper, taking Beijing metro line14Caihuying Station to Xitieying station interval tunneling under the Beijing Kowloon Canton Railway and Liuguang Railway premium risk source as the engineering background. Through numerical simulation with FLAC3D, research the settlement law of subgrade during the whole construction process of Shield tunnelling under the subgrade and analysis the effect of reinforcement measures on controlling the subgrade settlement. In the meantime, the conventional numerical simulation of shield construction method has been improved by using the geogridSELs built-in FLAC3D, so as to simulate the effect of shield friction on the ground deformation. During the shield tunneling process.The main research achievements are as follows:(1) Under the influence of shield friction, the soil around the shield produced obvious longitudinal displacement field; The surface heave in front of the shield and the settlement behind the shield are obviously increased compared with the circumstance without shield friction; The distribution of displacement field, stress field and strain field of the soil around the shield is more in line with the expected mechanical behavior compared with the circumstance without shield friction.(2) The shield excavation process accompanied by the expansion of the settlement trough, and the surface settlement caused by the left and right line tunnel construction has obvious effect of superposition. The surface settlement caused by the shield tunneling is mainly generated at the stage of shield pass settlement and shield tail void settlement. The differential settlement on both sides of the subgrade and the settlement rate of monitoring points are related to the location of shied.(3) Under the condition of no reinforcement measures,the settlement of Beijing Kowloon Railway sub grade and LiuGuang Railway subgrade caused by the shield under-passing are exceeded the10mm control requirements, The maximum vector value of longitudinal settlement measured in L=10m string exceeds the4mm control requirements. And the differential settlement on both sides of Beijing Kowloon Railway subgrade is close to the requirements of4mm. Therefore, to ensure traffic safety, it is need to take measures to reinforce the subgrade.(4) The reinforcement measures which are consist of subgrade grouting and radial grouting constructing after secondary grouting can effectively control the subgrade settlement. After strata reinforcement, the settlement risk indicators of Beijing Kowloon Railway sub grade and LiuGuang Railway subgrade are all satisfied with settlement control standard, the reinforcement measures get expected results. Besides, the reasonable selecting of reinforcement scheme and parameters can effectively improve the control effect.