Deformation Analysis Of Subway Deep Foundation Pit Excavation And Risk Management Of Support Collapse

In the current rail transit engineering construction environment,the subway station foundation pit has the characteristics of large excavation depth,tight construction period,low construction safety factor,complex surrounding structures,many safety hazards,and frequent accidents.Therefore,in order to ensure the safety and reliability of foundation pit construction and improve its construction safety factor,it is very important to predict the development status of the collapse risk of foundation pit construction,analyze its development law,and take corresponding control measures.This paper clarifies the main deformation parts and factors of foundation pit excavation from the aspects of deformation,damage and laws of subway foundation pit excavation;from the aspects of risk identification,analysis,evaluation,control,etc.,a method for the whole process of risk management is adopted,aiming to reduce The occurrence of collapse accidents.Taking the example of a foundation pit project in Guangzhou as the background,the main research contents and achievements are as follows:（1）Based on the finite element analysis method of MIDAS/GTS,the numerical model of the foundation pit was established to simulate the excavation of the foundation pit.Can provide reference for similar projects.Then,the actual deformation monitoring data of the main deformation parts of the foundation pit excavation site are compared with the deformation results of the main deformation parts of the foundation pit simulated by numerical simulation.The project is relatively consistent,indicating that it is feasible to use MIADAS/GTS to simulate the construction of the foundation pit and predict the excavation deformation of the foundation pit.（2）Based on the statistical analysis of collapse accidents over the years,the factors leading to the collapse of the foundation pit construction support were obtained,and then the factors leading to the collapse of the key parts of the foundation pit deformation were summarized on the basis of the construction quality,support structure Water penetration,geological conditions,untimely support,design scheme,underground pipelines,stratum disturbance,rainfall,soil sliding,settlement of surrounding buildings,undercurrent,over excavation,exposure,quicksand,expansion coefficient,etc.（3）Through the risk analysis and assessment of its risk factors through FAHP,it is concluded that the support collapse risk score is 0.4165,and the risk level is three,which is acceptable and conforms to the actual situation of the project.At the same time,the scores of the supporting structure,surrounding soil and pit bottom soil at the risk of supporting collapse risk are 0.4373,0.4502,and 0.2674 respectively,indicating that the most risky part is the surrounding soil,followed by the supporting structure.Finally,there is the bottom of the pit.（4）The use of BIM technology provides the whole-process control of the collapse risk of foundation pit support,which can understand the overall process dynamics of the risk in real time,obtain necessary information resources and hidden dangers in real time,and facilitate timely management and control measures.Through the 4D construction simulation,the reasonable planning of the progress can be realized before the construction,and the delay of the construction period due to the inappropriate progress planning can be avoided.Until the project is completed,the construction period is advanced by 40 days.Using BIM technology to simulate the construction process of each stage of earthwork excavation can effectively guide the sequence of earthwork excavation at the construction site.On this basis,this project reduces the number of excavators and earthmoving vehicles originally planned,which are 1 and 3respectively.vehicle.At the same time,visual disclosure and safety education can be carried out on the key construction procedures and difficulties of the support structure and foundation pit excavation in advance,which is helpful to control the safety of foundation pit excavation and support and improve the risk management level of the entire construction process.