Research On The Influence And Control Measures Of The Adjacent Subway Shield Tunnel Of The Deep Excavation

With the rapid development of China’s economic construction,the utilization of urban underground space has become an important part of China’s urban infrastructure.Construction would inevitably required near existing buildings as the development of urban underground space,and a large number of new geotechnical projects problem is emerged.The scale and depth of foundation pit excavation are getting larger and larger,and the surrounding environment is more and more complicated.The effects of unloading,precipitation,vibration,and loading during the excavation of the foundation pit affect the surrounding environment to varying degrees,causing deformation,inclination,uplift,and settlement of the existing structures.Especially when deep foundation pit construction is carried out around the subway shield tunnel,since the tunnel is very sensitive to these effects,not only the safety of the subway tunnel structure but also the safety of the subway operation must be ensured during the construction process.The design,construction and monitoring of pit engineering have higher requirements,which leads to a new topic of deep foundation pit excavation affecting the subway tunnel.Based on this background,in view of the characteristics of the influence of deep foundation pit excavation on subway shield tunnel,the common problems and control of this kind of engineering construction process are combined with indoor geotechnical test,model test,theoretical derivation and numerical simulation.The measures were carried out in a series of studies and some useful conclusions were obtained.The main work and research results are as follows:The influencing factors and control theory of the deformation of the shield tunnel of the near subway and the deformation law of the subway tunnel were to organize,summarize and generalize.According to the characteristics of the deep foundation pit project adjacent to the subway tunnels,the corresponding deformation control process for the adjacent subway tunnels foundation pit was proposed,and comprehensive measures were taken from the aspects of the surrounding environment,deformation control standards,deformation control design,construction process control,and post-construction evaluation.Finally,the results were applied to the calculation of engineering examples,and compared with numerical calculations and field measurements.Through the compression rebound test,the deformation characteristics of several common soils in Guangzhou were studied.The relationship between the rebound rate,rebound modulus and unloading ratio of each soil sample was studied.The test results showed that the unloading ratio was the key factor affecting the rebound deformation.The change of the void ratio of various soils was closely related to the applied load and the type of soil samples.On the basis of this research,the calculation formula of the rebound deformation of the soil under the pit excavation was deduced,and the calculated results were in good agreement with the measured values.And the measures to reduce the rebound deformation of the soil at the bottom of the pit were studied.In order to deeply study the influence of deep foundation pit excavation on the longitudinal deformation of the tunnel,based on the longitudinal equivalent continuous model,the influence of key factors such as joint stiffness and lateral deformation on the longitudinal equivalent stiffness of the shield tunnel was considered,and made corrections to derive relevant calculation formulas.According to the similarity theory,the model test was used to analyze the effective value of the longitudinal equivalent stiffness of the tunnel.On this basis,considering the interaction between the tunnel and the soil,the double-sided elastic foundation beam model was used to analyze the longitudinal deformation of the tunnel,and the coupling equation between the tunnel and the foundation soil was established.According to the law of rebound deformation of the soil at the bottom of the pit caused by excavation of deep foundation pit and the influence of longitudinal vertical deformation of the tunnel,two measures were applied to control the longitudinal vertical displacement of the tunnel caused by excavation of the foundation pit.Based on the numerical simulation method and the previous research results,the case analysis and summary research on the tunnel deformation control measures caused by deep foundation pit construction were carried out.Finally,the monitoring and control of the construction process was discussed.This article combined with the deep excavation engineering examples,based on the results of deformation control theory,experimental research and theoretical derivation,this paper discusses the design,construction practice and new characteristics and laws of foundation pit engineering under complex conditions to summarize,generalize and analyze the resules can provide some reference experience for similar projects.