Research On Construction Risk Of Subway Deep Foundation Pit Based On Fuzzy AHP Comprehensive Evaluation Method

With the rapid improvement of China’s economic level and the continuous advancement of urbanization,the role of subway as public transportation in urban construction is becoming more and more prominent.Different from general projects,subway construction often faces many challenges such as poor construction environment,technical difficulty and many uncertain factors.Therefore,it is particularly important to strengthen the risk management of subway deep foundation pit construction.First,this paper uses the WBS-RBS analysis method to identify the risk factors of subway deep foundation pit construction.Then analyzes the overall risk and the risk levels of various sub-items by combining the fuzzy analytic hierarchy evaluation method.Finally,formulate the corresponding risk factors based on the evaluation results risk control measures.The main research contents and results are as follows:(1)This paper takes the deep foundation pit engineering of a subway station in Hangzhou as the research object.On the basis of summarizing the previous cases of subway construction risk accidents,the Work Breakdown Structure(WBS)is used to breakdown the construction stage of the deep foundation pit of subway,and the risk sources with different properties are broken down by the Risk Breakdown Structure(RBS).By recombining them to form the preliminary risk identification list,and screening the most likely risks in the entire project according to the actual situation of the project,establish a risk index system for subway deep foundation pit construction.(2)According to the correlation between risk objects and the WBS-RBS risk identification results,a hierarchical structure model containing 9 types of risk events and 27 risk factors is established.Then compare the importance of risk factors at different levels according to the evaluation scale.Thus,a risk judgment matrix is constructed to determine the total ranking of risk levels and the influence weight set of risk indicators.(3)Use the fuzzy analytic hierarchy evaluation method to construct the risk evaluation model of subway deep foundation pit construction: Through the establishment of risk alternative set,the fuzzy quantization of the 27 risk factors mentioned above is carried out.With the help of expert experience and literature,the membership degree of the risk function of the project is determined.The first-level fuzzy evaluation matrix and the second-level fuzzy evaluation matrix are constructed respectively.On this basis,the risk level of each risk factor is evaluated in accordance with the principle of maximum subordination and established risk level classification standards.In addition,to formulate scientific and reasonable control measures and monitoring methods for high-risk sources to ensure the safety of deep foundation pit construction.The research results show that the deep foundation pit of a station is relatively safe as a whole,but there are still hidden risks.The construction risk level is medium risk(level III).It is necessary to pay attention to the changes of risk monitoring data at any time to adjust the construction situation in time.In the process of construction,the surrounding environmental damage(level Ⅰ)and foundation pit collapse sliding instability(level Ⅱ)have the greatest impact on the project,must reduce risk as much as possible.The analysis results are basically consistent with the risks appearing on the actual project site,which fully verifies the applicability and reliability of the fuzzy analytic hierarchy evaluation method in the risk assessment of subway deep foundation pit construction.It has practical guiding significance for risk management of similar projects in the future.