| Since the reform and opening up,the economy has continued to develop and the urbanization process has continued to deepen.Urban subways have developed vigorously,and a large number of excavations near subways have appeared.The excavation of the soil near the subway caused the operating subway tunnel to going up,resulting in frequent outages of the subway.At present,there are many case studies of the existing tunnel uplift caused by soil excavation.Excavation of the overlying soil layer has caused little research on the existing tunnel uplift.It is of great significance to study the existing tunnel uplift effect caused by the excavation of the overlying soil layer,which is important for protecting the existing subway tunnels and effectively using land resources.Based on the foundation pit project above an operating section of the Harbin Subway,this paper comprehensively analyzes the uplift effect of the existing tunnel caused by the excavation of the overlying soil layer through theoretical analysis,triaxial tests,field monitoring,and numerical simulation.Based on the analysis results,reinforcement measures are proposed.The main work of this article is as follows:(1)Derived two simplified calculation formulas for soil uplift caused by excavation under simple conditions.Based on the Bussinesq solution,the vertical displacement field function of the elastic half-space at any point under the surface rectangular uniform load is derived.(2)The undisturbed soil samples were taken and triaxial tests were performed to obtain the cohesive friction angle mechanical parameters of the undisturbed soil.On-site layered settlement monitoring was performed,and the floating displacements at different depths of the soil under the load of excavation were obtained.(3)Two simplified models were established,and a method for in-situ stress balance was obtained from the simplified models in the presence of stiff members in the soil.From the simplified formula and simplified model,three important parameters affecting the uplift amount are obtained: model thickness,rebound modulus,and excavation depth.An excavation model was established to simulate the tunnel uplift caused by each excavation process.According to the simulation results,reinforcement measures were proposed,and a reinforcement model was established to simulate the tunnel uplift caused by each excavation process after reinforcement. |
