Research On Construction Risk Assessment Of Urban Shallow-buried Large Span Underground Excavation Engineering

With the large-scale development of urban underground engineering in our country,the underground engineering constructed by underground excavation tends to be ultra shallow buried and large-span.Shallow buried large-span underground excavation project has the characteristics of complex geology and surrounding environment,large project volume,complicated construction process and long construction period.In addition,the uncertainty and objective universality of risks make construction accidents occur frequently in recent years.Therefore,relying on the national key research and development project "coupling evolution mechanism and safety evaluation system of major risks in urban underground large space construction"(National Key R&D Program of China(2018YFC0808701)),this study takes the analysis of accident characteristics as the breakthrough point,and uses the methods of literature inquiry,mathematical statistics,WBS-RBS,expert investigation and fuzzy comprehensive evaluation to carry out risk assessment research on urban shallow buried large-span underground excavation project Research:(1)The paper conducted statistics and analysis of 295 underground project construction accidents in the past 15 years.Using the method of mathematical statistics and analysis and induction,it carried out the statistics and analysis in terms of the year of the accident,the geology of the accident area and the type of accident.The paper also carried out detailed analysis on the laws between the year of accident,the casualty,the type of accident,the direction of accident risk source and geology of areas.(2)The paper summed up a risk index system for the construction of urban shallowburied large span underground excavation project.The cause-effect diagram analysis method which is based on the analysis of accident cases was used to analyze the accidents with high incidence rate such as collapse,water penetration and falling accident from high place.Cause-effect analysis diagram of accidents was established from five aspects: geology,surrounding environment,planning and design,construction technology,and management.And on this basis,a risk evaluation index system for urban shallow-buried large span underground excavation construction was formed.(3)Aiming at the risk characteristics of the construction of urban shallow-buried large span underground excavation,the weight correction coefficient is introduced on the basis of the traditional fuzzy comprehensive evaluation method,and considering the spatiotemporal effect during construction and the disturbance effect of pre-work.The concept of disturbance coefficient was proposed,and finally a dynamic risk evaluation model based on fuzzy comprehensive evaluation method was formed.And the method for determining the specific parameters of the model was given.(4)The paper analyzed the examples using dynamic evaluation methods.The risk dynamic evaluation method based on fuzzy comprehensive evaluation method was used to carry out the dynamic risk assessment of the whole construction process of specific project.The construction process was divided into six stages,and the MATLAB software was used to write dynamic evaluation codes for calculation.According to the evaluation results,corresponding protective measures were taken,and the entire construction process was monitored and measured.It was found that the monitoring data of the entire construction process were normal,which did not affect the normal operation of the Taiyuan Station,and further proved that the risk control measures were reasonable and effective.(5)The comparative study method and traditional static evaluation method were used to evaluate the same project.Comparing the evaluation results of the two methods,the accuracy of the dynamic evaluation method was verified.