Risk Assessment Methods And Countermeasures For Floods Of Metro System In Subsiding Environment

This study applied the fuzzy analytical hierarchy process(AHP),geographic information system(GIS),and storm water management model(SWMM)to assess the risks induced by flooding disasters for metro systems in subsiding environments.These methods include two analysis types: from(i)regional to local and(ii)qualitative to quantitative.The study focuses on the following five aspects of scientific and engineering problems:(a)approaches for identification and assessment of risks for metro systems;(b)consistency of the fuzzy judgment matrix and determination of fuzzy numbers;(c)risks for metro systems induced by subsiding land;(d)risk assessment of flood disasters for metro systems in subsiding environments;(e)suggestions for disaster prevention for the safe operation of urban infrastructures.This study presents the following innovative results:(1)An expert system analysis is proposed to determine the fuzzy number in fuzzy AHP(FAHP).Based on the shortcomings of the traditional expert survey method,the "1–9 degree standard" expert system analysis method is proposed.The influence of each assessment factor on the risk is quantified from 1 to 9.By summarising the scores of each factor and selected times of each score,the corresponding fuzzy number is determined to obtain the importance of the assessment factors.This method is used to determine the interval fuzzy number of interval FAHP,the triangular fuzzy number of triangular FAHP,and the trapezoidal fuzzy number of trapezoidal FAHP.The proposed expert system analysis determines the fuzzy numbers and establishes fuzzy judgment matrices.The metro tunnel construction in Jinan is used as case study to identify the risks and factors affecting safety.(2)The settlement risk of a metro system induced by subsiding land is assessed.A land subsidence risk assessment system was established to determine the settlement risk along metro lines.The results are used to assess the settlement risk of the metro system.Regarding a subjective perspective and based on the risk assessment system,the expert system analysis method is applied in trapezoidal FAHP to determine the trapezoidal fuzzy weights of the assessment factors.Regarding an objective perspective,the middle intervalbased set pair analysis(SPA)is used to analyse the difference between the actual value of the assessment factor and the criterion value of the grade.The trapezoidal FAHP and SPA methods are combined to assess the regional risk of land subsidence.Finally,the settlement risk along the metro line is obtained based on the regional risk level.(3)The flood risk of a metro system is assessed.The flood risk of a metro system is assessed combining subjective and objective methods.Regarding a subjective aspect,the expert system analysis method is applied to interval FAHP.The weight of the assessment factor is expressed by the interval fuzzy number.Regarding an objective aspect,the fuzzy clustering analysis method is adopted to determine the objective weights of the assessment factors.The objective weights are used to modify the subjective weights and to determine further the fuzzy cluster centre matrix and fuzzy cluster membership of the assessment sample.The Shanghai metro system is used as case study to establish the assessment system and analyse the regional flood risk level.Based on the regional flood risk level,the risk level of the metro system is assessed according to the risk level along the metro line.The results show that the metro system in the urban centre exhibits a high flood risk.(4)The flood risk in the subsiding environment of a metro system is predicted.Through a data conversion between SWMM and GIS,an algorithm for the runoff diffusion is proposed to simulate the inundation depth of the ground for different rainstorm scenarios.A generalised equation is proposed to determine whether the station will suffer from floods.Based on the results of(2)and(3),the high-risk area in the centre of Shanghai with regard to floods is taken as case study to model the inundation risks for scenarios with different rainstorms and settlements.According to the results,in an extreme rainstorm,the inundation in the metro station mainly occurs in areas with serious land subsidence.The region along the Huangpu River and Changning and Yangpu districts might possibly suffer from inundation.The result for the inundation risk of the metro station show that the Longyao road station and Yangshupu road station of Line 11 and Xinjiangwancheng station and Yingao East road station of Line 10 might possibly suffer from inundation.(5)The planning countermeasures for a safe operation of the Shanghai Metro System are proposed.The flood risk of the metro system is related to the risk induced by land subsidence.Regional land subsidence is one of the important flood risk factors for significant infrastructures.Based on the assessment of the land subsidence in Shanghai,more attention must be devoted to regions within significant infrastructures,e.g.Jiading Automobile City,Baoshan Iron and Steel Co.,Ltd.,and Pudong Airport.The countermeasures for the flood control in the subsiding environment are classified with levels I–V(high–low)according to the flood risk and settlement risk of the metro system.The metro lines in the urban centre are suggested to take prevention measures.Further,the flood prevention measures of metro stations with high flood risk are classified via five levels: I-I,I-II,I-III,I-IV,and I-V(high–low).Longyao station and Yangshupu station should devote more attention to flood prevention.The metro lines that pass through Huangpu River should install water stop doors at both ends of the river and adopt drainage facilities at the lowest part of the line section to reduce flood impacts caused by high tides of the Huangpu River.