Study On Settlement And Treatment Methods Of Operating Subway Tunnel

Currently,the development and utilization of underground space has been paid more and more attention from all countries around the world to overcome the increasingly problems on the ground such as serious traffic congestion.Subway,due to its advantages of running speed,riding fast and impervious of road traffic congestion,has become an important mean of public transport in big cities of China.However,with the increase of the tunnel construction period and the long-term operation of the subway,there may be settlement appearing in the tunnel,which is affected by many factors such as regional ground settlement,soil vertical heterogeneity,surrounding tunnel excavation,surface loading above the tunnel,leakage of the tunnel,loading and vibration of the train,and so on.Long-term settlement may affect the normal use of the orbit,moreover,the uneven settlement may directly cause serious security accidents.Taking west side tunnel of Beijing subway airport Line T2 as an example,this study aims to address the tunnel dislocation deformation problems from three aspects of theoretical analysis,numerical simulation,on-site monitoring.Finally,this paper developed a methodological framework including theoretical prediction,simulation design,and effectiveness evaluation.Therefore,it can be used as a reference for dealing with settlement with similar strata of the tunnels in Beijing or other areas in China.Specifically,the main work and contents of the study can be drawn as follows:(1)The factors affecting the settlement of the subway tunnel structure were determined from a qualitative perspective.We found that the main factors include geological conditions,weak formation,uneven thickness distribution,tunnel leakage and vibration.Based on the real observations,a simplified hyperbolic model was employed to quantitatively predict the long-term settlement of the tunnel structure.The results indicate that the fitting values of the model are nearly coincident with the monitoring values.(2)In terms of the saturated clay,silt and silty sand strata in the study area,a set of monitoring technology methods were constructed to monitor the long term operation of subway settlement.The monitoring of settlement before construction,dynamic monitoring during construction and long-term monitoring data after construction were guided by a scientific and reasonable information monitoring technology,which lays a foundation for guiding settlement management in research area.(3)Using a three-dimensional numerical simulation method,the fictitious expanding pressure method was used to simulate the lateral grouting reinforcement.Comparative analysis of the settlement characteristics of two kinds of simulation schemes,we found that two-wheel grouting is more reasonable to realize the tunnel structure and the road bed uplift.(4)The process of grouting reinforcement was mainly divided into seven stage.The characteristics of the formation reaction after each grouting stage were analyzed,and the reaction characteristics of the common portland cement and superfine cement were compared and analyzed.(5)By comparing the numerical simulation results with the observed data,this paper demonstrates the rationality of simulating the reinforcement effect of the lateral grouting by a virtual expansion pressure method,and then put forward an method for evaluating grouting effect of the existing long term operation tunnels.The results show that the scheme of two-wheel grouting reinforcement treatment for west side tunnel of Beijing subway airport Line T2 is reasonable and feasible.