| In recent years,with the rapid development of China’s urban modernization and the sharp increase of population,the contradiction between the expansion of land demand and the shortage of overland space has become increasingly apparent.Therefore,rational development and utilization of underground space has become increasingly urgent,especially the rapid development of urban underground railway construction.As the subway line will inevitably run through the important areas of the city,the deep foundation pit of subway station is mostly located in the area with narrow site and strict environmental conditions,which brings many adverse effects to the construction of foundation pit project.In addition,due to the variability of urban strata,the complexity of surrounding environment and the uncertainty of engineering impact,once an accident occurs,it may endanger the safety of the foundation pit itself and surrounding environment,resulting in different degrees of economic losses or even casualties and causing adverse social impact.Therefore,as an important part of underground railway construction,it is necessary to know the safety of deep foundation pit engineering accurately and comprehensively,and to control its possible risks effectively.In the construction process of deep foundation pit,the common security problems are mainly manifested as support system damage,soil infiltration damage and surrounding environment damage.Such as excessive displacement and deformation of the retaining structure,fracture and overall instability,basement uplift,inrush,piping and quicksand,and uneven settlement of the surrounding surface,road cracking,pipeline cracking,cracks and tilts of adjacent structures caused by excavation of foundation pit and construction of retaining structure.According to the above the safety of deep foundation pit engineering problem,the construction of deep foundation pit of subway station under two typical strata in Beijing and Tianjin are taken as the background.Through analysis and study of engineering geology,hydrological characteristics,basic size of the subway station foundation pit,supporting structure type,data of retaining structure and the surface deformation,combined with the existing a large number of relevant research results,focus on the deformation characteristics,the safe and stable,environmental impact,project risk analysis and control study.The purpose of this study is to form an engineering safety management system that integrates design,construction and monitoring and can make overall planning for urban rail transit construction under complex stratum conditions.Main work and research results of this paper include:(1)Based on the statistics and analysis of a large number of measured deformation data of the working shaft foundation pit project of qinghuayuan tunnel of beijing-zhangjiakou high-speed railway,Beijing metro line 6,tianjin metro line 5 and line 6,the deformation characteristics of the foundation pit under different geological and hydrology conditions are obtained,and the deformation indexes are selected from multiple perspectives for comparison.At the same time,taking the Beijing area as an example,the foundation pit is classified and studied according to the strata characteristics and size,and the concept and research method of the overall deformation mode of the subway station foundation pit considering the space effect are put forward,and the overall deformation rule is obtained.(2)Through comprehensive consideration of computational mechanics model,foundation pit plane and excavation size,stratum and groundwater distribution,soil strength anisotropy and other factors,the formation of targeted,suitable for different characteristics of the foundation anti-uplift,groundwater seepage and other safety and stability analysis and calculation method;At the same time,according to the main work content of environmental impact analysis,the analysis process of the influence of foundation pit excavation on the surrounding environment is given.(3)Through the establishment of the Beijing and tianjin and stratigraphic distribution and standardized model of subway station deep foundation pit excavation surrounding environment represented by buildings,from the excavation effect on deformation of building and design scheme of foundation pit engineering and building relationships with the relative displacement of foundation pit,the excavation in different formation conditions and the interaction between adjacent buildings a multi-angle analysis and evaluation,feedback on excavation influence degree to the environment,the influence of excavation on the surrounding environment and form various angles comprehensive evaluation method.(4)Based on the analysis of the typical serious safety accidents in the foundation pit of subway station and the related data of some foundation pit projects in Beijing and tianjin,the risk factors of the two projects are determined and summarized.Taking the actual project in Beijing and Tianjin as an example,the standardized stratum and foundation pit model are established,and corresponding risk control measures are put forward according to the actual needs of the project.By means of numerical simulation,orthogonal test and theoretical analysis,the design and implementation method of measures and the influence of main design parameters on the control effect are studied in depth.At the same time,the determination process of control measures and the mechanism of control measures are given. |
