Mechanism of karst ground collapse and evaluation of disaster risk in Chengnan community,Yingde City,China

WANG Heng; YAO Yijuan; ZHAO Kui; CHEN Yudao; QIN Jiaxiao

doi:10.11932/karst2025y007

Abstract：Karst ground collapse is one of the most common geological hazards in karst areas.It is characterized by concealment,sudden occurrence and inhomogeneity,along with various other complex features.Understanding the mechanisms of karst ground collapse and conducting risk assessments for such events are of great significance for urban development and engineering construction.In November 2020,a large-scale karst ground collapse occurred in Chengnan community of Yingde City,Guangdong Province.A total of 31 collapse pits were identified,predominantly exhibiting elliptical and circular shapes,and spatially distributed in three strips.The duration was notably lengthy,resulting in relatively severe disaster impacts. Comprehensive investigation results and analysis show that the karst ground collapse in the study area primarily occurred in the main groundwater runoff zone,which is characterized by relatively thick overlaying layers and significant karst development.The spatial distribution of the strip align with the arrangement of three fault zones in the study area.In the vicinity of a sewage treatment plant,the stacking of karst caves is evident,characterized by a significant cumulative thickness of the caves,high permeability of the rock layers,and loose overlying soil with low cohesion.These factors created fundamental conditions for the concentrated occurrence of ground collapse.In the study area,the triggering mechanisms of karst ground collapse are influenced by frequent fluctuations in the water levels of the nearby Beijiang River,as well as human activities that involve groundwater pumping and draining.These factors induce hydrodynamic effects,including subsurface erosion and vacuum suction erosion of groundwater.Additionally,the presence of sewage leakage near the sewage treatment plant at the center of the study area altered hydrochemical properties of groundwater,resulting in chemical dissolution.Therefore,the primary mechanisms driving karst ground collapse in this area are chemical dissolution and hydrodynamic effects. In order to facilitate the formulation of targeted preventive measures,we selected eight susceptibility indicators and two vulnerability indicators after screening each indicator factor in the study area.These indicator factors were combined with the Analytic Hierarchy Process(AHP)to establish a comprehensive index model of karst ground collapse risk suitable for the study area.By leveraging GIS spatial analysis functions,we conducted a relatively accurate risk assessment of the study area.The results show that the risk of karst ground collapse in the study area can be categorized into two levels:high-risk and moderate-risk.The high-risk zone is mainly distributed around the sewage treatment plant and cement plant area,comprising 70.83％of the total study area.Conversely,the moderate-risk zone is mainly located in the northwest corner of the study area,accounting for 29.17％of the total. In conclusion,it is recommended to strengthen the dynamic monitoring and management of groundwater,along with implementing measures to prevent and control surface sewage seepage.These actions are essential to protect the region from ground collapse hazards and to reduce the risk of disasters.