Risk Assessment Of Earth Fissures In The Su-Xi-Chang Area Based On Grey Relational Grade Theory

Su-Xi-Chang area is one of the most severe ground fissure disaster areas in China,which has caused huge economic losses.The ground fissures causes surface rupture,dislocation of underground pipelines,drying up of wells and failure of buildings on the ground.Therefore,it is of great practical significance to accurately predict when and where ground fissures will occur by using the existing geological survey data of Su-Xi-Chang.In this paper,the factors affecting the development of ground fissures in Su-Xi-Chang area are determined by geological exploration data and genetic mechanism.Then,based on grey relational degree theory,the weight of each factor is determined.Finally,the risk zoning of ground fissures in this area is carried out based on Arc-GIS platform.The main conclusions are as follows:First,the Su-Xi-Chang ground fissures have obvious characteristics of space-time,direction and symmetry,sustainability and clustering.The affecting factors of ground fissures development can be divided into two category:geological structural and human activities factors.The geological structural factors include the depth of bedrock to the ground surface,the undulation of bedrock surface,the thickness of the second confined aquifer and the clay layer,and the human activities factors include the water level of the main mining layer(the second confined aquifer)and the cumulative ground subsidence.Second,the decreasing order of correlation degree of six influencing factors:water level drop of main mining layer,thickness of second confined aquifer,depth of bedrock,cumulative ground subsidence,undulation of bedrock and thickness of cohesive soil layer.This shows that the water level drawdown of the main mining stratum and the thickness of the second confined aquifer are most closely related to the development of ground fissures in Su-Xi-Chang,and the effect on ground fissures is the most significant.It also proves that the ground fissures in Su-Xi-Chang are caused by excessive exploitation of ground water from the second confined aquifer.Third,the influence weight is 16.56%for the bedrock depth,16.43%for the bedrock undulation,16.86%for the thickness of the second confined aquifer,16.22%for the thickness of clay soil,17.43%for the water level of the main mining layer falls,and 16.50%for the cumulative ground subsidence.Among them,the water level of the main mining layer has the strongest influence weight,and the thickness of cohesive soil has the weakest influence weight.Finally,the most risk areas of ground fissures in Su-Xi-Chang area are located in the east and south of Changzhou,the west of Wuxi,the south of Jiangyin,and the area around Zhangjiagang.The second most dangerous areas are located in the west of Changzhou and the east of Wuxi.The transition areas from dangerous to safe area are located in the east and south of Suzhou,and the safe areas are scattered in eastern Suzhou and around Kunshan.