Risk Assessment Of Collapse Disaster In The Limestone Area Around The Mountain Region In The Southeastern Sichuan Basin

The southeast basin area of Sichuan Basin belongs to the transition zone between Sichuan Basin and Yunnan-Guizhou Plateau,with complex geological structure,strong river cutting,significant topographic differences,mountainous terrain,lithology dominated by limestone,the research area includes a number of large scenic spots and reservoirs,and the population is dense,but collapse disasters are frequent,there are many risk factors in the region uncertainty,the occurrence of collapse disasters will cause major economic losses and casualties in the region.The investigation and risk assessment of geological disasters in this region are of great significance to disaster prevention and mitigation.In this study,60% of the mountainous limestone areas with an elevation greater than 1000 m in the mountainous areas around the southeast basin of Sichuan,namely Wulong,Nanchuan and Qijiang were selected as the research objects,and the contribution rate method and entropy weight method were used to establish a collapse disaster risk evaluation model.Combined with the characteristics of human activities in the limestone area around the mountainous area of the southeast basin of Sichuan,expert opinions and analytic hierarchy methods were used to construct the vulnerability evaluation model of collapse disasters in the study area,and the risk zoning evaluation,vulnerability evaluation and risk evaluation of the study area were realized by using Arc GIS software,and the main research results obtained were as follows:(1)The limestone area around the mountainous area of the southeast basin of Sichuan was selected to analyze its topographical characteristics,geological characteristics,hydrogeology and human activity characteristics,and the distribution characteristics of collapse disasters located on steep cliffs.Taking the dangerous rock group of the Jinfoshan Zhiziyan aluminum ore plant in Nanchuan District as an example,the stability evaluation of the dangerous rock group here was carried out by the reliability method,and the simulation results of Rockfall software were used to determine the collapse disaster threat area and evaluation.(2)Based on the characteristic analysis of the mountainous limestone area in the southeast Sichuan basin,nine influencing factors for the risk assessment of collapse disaster were selected,and the collapse disaster risk evaluation index system was constructed for the lithology of the strata,the relative height difference of the steep cliff,the elevation,the average annual rainfall,the topographic slope,the vegetation cover,the distance from the water system,the distance from the fault structure,and the distance from the road.The contribution rate distribution map of single factor was obtained by the contribution rate method,and the influence factors were quantitatively divided into four hazard levels of very high risk,high risk,medium risk and low risk by the isometric method,and the Pearson correlation coefficient of each factor obtained by SPSS software was used to verify its rationality.The entropy weight method was used to obtain the weight coefficient of the risk influence factor,and the collapse disaster evaluation model coupled with the contribution weight model and the entropy weight method was constructed,and the multi-factor superposition and zoning were realized by borrowing Arc GIS software,and the results showed that the proportion of risk in the study area was mainly in the high-risk area and medium-risk area,the area of the extremely high danger area accounted for 11.38%,the medium-risk area accounted for33.13%,the high-risk area accounted for 29.61%,and the low-risk area accounted for25.88%.Using the prediction accuracy and criteria of the model,the accuracy rate of this evaluation was 91.7%.(3)From the two aspects of population vulnerability and material vulnerability,five vulnerability evaluation indicators of residential population distribution,land transportation facilities,water conservancy facilities,civil and industrial buildings and scenic spots were selected,and the weight coefficient obtained was calculated by analytic hierarchy method,and a mathematical model of vulnerability evaluation of limestone area in the mountains around the southeast basin of Sichuan was established,based on the spatial multi-factor superposition of Arc GIS system,and the vulnerability zoning was carried out using the natural discontinuity method,and the area area of extremely high vulnerability(IV.)accounted for 3.56%.The area with high vulnerability(III.)accounted for 15.35%,the area with medium vulnerability(II.)accounted for32.59%,and the area with low vulnerability(I.)accounted for 48.50%.(4)Arc GIS software was used to multiply and superimpose the risk zoning evaluation results and vulnerability evaluation results in the study area,and the risk zoning was completed according to the natural discontinuity method,and the zoning results showed that the area of very high-risk areas accounted for 8.45%.The area of high-risk areas accounted for 20.91%;Medium-risk areas accounted for the largest proportion of area,36.14%;The proportion of low-risk areas was 34.49%.According to the collapse disaster points,risk assessment factors and vulnerability evaluation factors that have occurred,the affected bodies and disaster causing bodies in various levels of collapse risk areas in the study area were analyzed.Thirteen townships are in very high-risk areas,2 townships are in high-risk areas,4 townships are in medium-risk areas,and 3 townships are located in low-risk areas.