Research On Risk Management Of Open Cut Metro Deep Foundation Pit Based On Field Monitoring

In recent years,China’s urban rail transit has entered a stage of vigorous development,and various high-rise buildings are also increasing,resulting in a large number of deep foundation pits.The scale and complexity of foundation pit engineering are increasingly developing in the direction of "deep,large,tight and close",and the safety of its construction has become a research hotspot in the engineering field.The construction period of deep foundation pit engineering is long,involving a wide range,and there are many influencing factors,so it is difficult to evaluate the risk state of the deep foundation pit scientifically.In order to ensure the safety of urban subway construction and avoid possible safety accidents,it is of great significance to accurately and comprehensively evaluate the safety risk of open cut subway station engineering during the construction period.Combined with the characteristics of the project,this paper carries out the static and dynamic risk assessment.The main research results are as follows:(1)Based on the risk of subway deep foundation pit and the characteristics of subway foundation pit engineering,this paper systematically expounds the safety risk assessment process of subway station foundation pit,and carries out statistical analysis on the responsible units and causes of subway foundation pit accidents.The statistical results show that the engineering accidents caused by construction units account for more than half,and water related accidents account for a large proportion.(2)Based on the analytic hierarchy process and entropy method,a fuzzy comprehensive evaluation model for the safety risk of open-cut subway deep foundation pit construction is established.The normal function is selected as the form of the membership function,and the risk value is assumed to be the most fuzzy in the adjacent risk level boundary.To establish the membership function,and combine with the "Urban Rail Transit Underground Engineering Construction Risk Management Specification" to establish the evaluation set of the fuzzy comprehensive evaluation model.(3)Considering the characteristics of the project,the static risk evaluation index system is established based on WBS-RBS,and the static risk assessment before the construction is carried out according to the expert scoring;By selecting important and representative monitoring items,the dynamic risk assessment index system is established,and the dynamic risk assessment is carried out according to the monitoring data of a certain day in the construction process.Based on the whole construction monitoring data,the dynamic change chart of risk probability and risk grade score of foundation pit is drawn.For the static and dynamic assessment results,the risk level of each risk is determined according to the principle of maximum membership degree.(4)This paper optimizes the criteria of risk index grade through the theory of fuzzy mathematics,so that in the risk assessment activities,not only can the rich experience of experts be effectively used for scoring evaluation,but also the fuzzy influence of experts on risk assessment can be eliminated.It is a reasonable method to solve the ambiguity of risk level boundary.