The Study Of Surface Subsidence Caused By Metro Shield Construction

With the development of our economy and the increase of population,the traditional traffic jams in cities have become more and more serious.The construction of subway has become one of the important ways for people to solve the congestion problem.The construction of shield tunnels has been widely applied to the construction of subways because of its features of safety,convenience,speed,and small impact on the ground.However,due to the complex geological conditions and limited construction levels at many times,the engineers have to face the problems of the surface subsidence.How to control surface subsidence is a key issue that people need to solve urgently in subway tunneling.The main contents and results of the research are:1.Based on the tunnel construction method of a shield tunnel construction method of Wuhan Metro,and the analysis of the mechanism of surface settlement caused by the shield method,combined with the on-site investigation and statistics,the compare the suitable condition of the earth pressure balance shield machine and the slurry balance shield machine.Making a brief analysis and study of the shield type selection for the construction plan,we draw a conclusion that the slurry balance shield machine are suitable for geological conditions that gravel,coarse sand and so on,while the earth pressure balance shield are suitable for the geological conditions such as muddy soil and clay area.In this paper,the geological conditions are mainly silty clay,silt,clay and so on.Considering this project,it is appropriate to use an earth pressure balance shield machine.During the shield tunneling process,the heavy and difficult points in the construction were analyzed and studied,and corresponding protective measures were formulated.2.According to the actual situation of the project,the tunneling process was simulated using finite element software Midas/GTS.In the construction process,different thrusts of the shield machine are used,and the simulation results yield the corresponding surface settlement.Ground surface subsidence change curves with different thrusts are obtained respectively,and analysis the change rules.Then the simulation results are compared with the actual subsidence curves.The two results are approximately the same,It indicates that the feasibility of the simulation results.Different thrusts have different influences on land subsidence.The smaller the thrust,the greater the land subsidence,instead,the smaller the land subsidence.By comparing the measured data with the simulation results,the reasonable thrust should be at least 8000 k N.3.Finally,the factors of the control of ground surface excavation parameters are analyzed,the control of the slag amount,the reasonable formulation of the earth pressure,the timely grouting and the adequate grouting amount all have the direct effect on the land subsidence.The shield tunneling is similar to the engineering geological conditions.The rational development of parameters is of guiding significance.