Study On Risk Analysis And Reinforcement Measures For Re-enabling Deep Foundation Pit

With the development of social economy in China,people's demand for living space is increasing.Under the premise of limited land resources,how to meet the rapid growth of population and people's demand for living space has become a difficult problem.Nowadays,the development of surface space is nearly saturated,so many experts and scholars have shifted their goals to the field of underground space.Deep foundation pit is the foundation of underground space development.Its construction technology is complex,management is difficult,and construction accidents occur frequently.In order to avoid construction accidents,risk analysis of deep foundation pit is essential.The main object of this paper is the deep foundation pit which can not or suspend the follow-up construction after the completion of the deep foundation pit support construction for some reason.Its idle time exceeds its own design support period or the two-year support period stipulated by the code.In the risk analysis of this kind of restart foundation pit,the risk factors are determined on the basis of the traditional risk analysis of deep foundation pit combined with its own characteristics.In this paper,firstly,the risk analysis of this type of deep foundation pit is carried out to find out the most sensitive risk factors.Secondly,the numerical simulation of sensitivity factors is carried out by Abaqus,and the optimization scheme of reinforcement and support is determined.Specific research contents are as follows:1.Study the construction process and method of deep foundation pit,systematically summarize the literature of construction management and risk analysis of deep foundation pit at home and abroad,understand the research status of deep foundation pit risk at home and abroad,make a summary of the background of this research topic,and provide a theoretical basis for the following research.2.Collect a large number of literature on deep foundation pit accidents,summarize the causes of deep foundation pit accidents,find out the main risk sources of traditional deep foundation pit accidents,and through exchanges with experts and scholars,on the basis of traditional deep foundation pit risk sources,combined with the characteristics of re-opening deep foundation pit after idle time exceeds its own support period,establish six types of risk sources,and subdivide them into 16 risk factors.Through the Delphi method to investigate the risk factors,the probability of 16 risk factors is obtained by preliminary calculation.3.The Bayesian network graph method is used to calculate the prior probability,the posterior probability and the connection probability of the risk factors of deep foundation pit.The risk probability of the whole event is calculated through the transitivity of the Bayesian network.Using the diagnostic reasoning function of Bayesian network and using Netica software to calculate the posterior probability of 16 risk factors,the degree of the impact of each risk factor on the overall risk of re-opening deep foundation pit is obtained,and through the sensitivity analysis function of the software,the sensitivity of risk factors is analyzed.Finally,the order of the sensitivity of risk factors is obtained,and the re-starting is found.The maximum risk source of deep foundation pit is used to determine the control target.4.Using Abaqus software to simulate the deep foundation pit,through the strength reduction method to simulate the aging process of the supporting structure of the deep foundation pit,the deformation law of the supporting structure and the soil around the deep foundation pit is obtained.By simulating the control effect of setting reinforcement support at different locations on the deformation of the original supporting structure and the soil around the deep foundation pit,the reinforcement support is determined.The optimum location can achieve the optimum scheme of deep foundation pit reinforcement.