Research On Risk Assessment Model And Application Of Small-spacing Shield Construction

With the continuous update and progress of rail transit construction technology,and the increasing demand of the people for urban rail transit,the construction of urban rail transit has been advancing rapidly.However,in the old central area of the city,due to the space constraints of existing buildings(structures)along the line,the space of the shield tunnel is compressed.The distance between the two tunnels is getting smaller and smaller.The situation is becoming more and more common..Compared with the standard-spacing shield construction of double-line tunnels,it is more complicated and more likely to cause safety accidents.Therefore,the use of efficient,accurate and practical methods to conduct safety risk assessment and engineering practice guidance on various uncertain risk factors under close-space shield construction has pioneering theoretical significance for the control of close-space shield construction risks.Spacing shield construction also has strong application value in actual engineering.In response to this research topic,this paper has carried out the following work.First,the main risks of small-spacing shield construction are obtained by analyzing the interaction mechanism among “shields,soil layers and tunnels” and the spatial effect of the disturbance of this construction.And by comparing the theories of risk assessment management and combining risk features of the small-spacing shield construction,a cloud model is selected as the risk assessment method of this construction.Next,the WBS-RBS method is used to comprehensively identify risk sources of the small-spacing shield construction in each stage,to construct a risk coupling matrix for this construction,and to form a list of risk sources.Then,the ideas and key steps of building the risk assessment model for the smallspcaing shield construction are elaborated.First,the weights and risk levels of indicators at all levels are determined by the entropy weight method and the risk matrix method.And then the forward and backward cloud generation algorithms based on the cloud model are used to create the assessment cloud of criteria and standards.Finally,the risk assessment result is synthetically determined via the comparisons of cloud maps and similarity.At last,this thesis applies the risk assessment model to the small-spacing section of a subway tunnel.Based on the scoring data of expert interviews,the cloud model algorithm and entropy weight method are used to obtain the index evaluation cloud at all levels and the index weights at all levels,and the construction risk evaluation cloud chart and the comprehensive cloud chart for each first-level index evaluation are generated through MATLAB to determine the overall risk level of the project It is intermediate level and proposes corresponding risk response measures for key risk sources at each stage.The risk level calculated by the model built in this thesis and the proposed control measures are consistent with the actual situation,which verifies the validity and practicability of this model.