Deep Pit Construction Based On Dynamic Fault Trees Security Risk Analysis And Control

In recent years,with the acceleration of urban development and construction in China,the demand for urban underground space has been increasing to meet the needs of urban construction land.The number of various underground engineering projects such as subway stations,underground parking lots,and tunnels is gradually increasing.Due to the "complex construction environment,large engineering volume,and high safety risks" of deep foundation pit engineering,the difficulty of risk management in construction has been increased.Therefore,this paper conducts research on risk analysis and control of deep foundation pit engineering based on the dynamic fault tree analysis method.Firstly,by studying the relevant literature on risk analysis in deep foundation pit construction at home and abroad,we explore the insufficient consideration of the dynamic nature of deep foundation pit construction in previous studies,and use this as a starting point to conduct research on dynamic risk management in deep foundation pit construction.By collecting data on deep foundation pit accidents that have occurred in China and conducting statistical analysis,we determine patterns such as the number of accidents and the regions in which they occur.By statistically analyzing the main types of accidents and the causes of accidents,we identify high-frequency risk factors,laying the foundation for subsequent identification of risk sources in deep foundation pit construction.Secondly,the construction process is decomposed into five stages: survey and design stage,earthwork engineering stage,support engineering stage,dewatering stage,and monitoring stage,using a work breakdown structure.The comprehensive and systematic identification of safety risk factors in deep foundation pits is carried out using a risk breakdown structure and the 4M1 E principle.The risk factors are decomposed into five aspects: personnel factors,mechanical equipment,construction materials,construction techniques,and environmental factors,and key construction risk sources are retained.A list of 22 risk sources for collapse in deep foundation pit construction is obtained.Based on the results of safety risk identification in deep foundation pit construction,a dynamic fault tree model of deep foundation pit collapse accidents is constructed according to the accident mechanism.Taking the improper excavation work fault tree as an example,modular decomposition is carried out to identify dynamic and static sub-trees.For the static sub-trees,the minimum cut set and the probability of occurrence of the top event are determined using the binary decision diagram method.For dynamic sub-trees,they are transformed into Markov chains to determine their fault modes and to quantitatively analyze the probability of top events.Based on the dynamic fault tree model,simulation is carried out to obtain the probability of occurrence of accidents caused by improper excavation work in deep foundation pits and the changing patterns of the probability importance of each bottom event over time.Based on this,corresponding prevention recommendations are put forward for different stages of deep foundation pit construction projects.Taking a collapse accident in a deep foundation pit in Yangzhou city as an example,the actual cause of the accident is compared with the results obtained from the risk analysis using the dynamic fault tree,which verifies the rationality and practicality of using this method for safety risk analysis in deep foundation pit construction.According to the actual situation of the deep foundation pit project in the sub-center of Beijing,the foundation pit water gushing dynamic fault tree is established.Through the analysis of model simulation results,determine the main risk factors in the construction process of the project,using the simulation software for the probability of the probability of the bottom event probability changes over time,the probability of the project accident change rate from slow to fast,to 180 days the probability of water accident reaches 0.0018.The change curve and size ranking of the probability and importance of each bottom event are obtained,and the corresponding construction suggestions and risk control measures are put forward,which provide reference for the construction site management and risk prevention of deep foundation pit engineering,and have practical guiding significance for the safety risk management of similar projects in the future.