Study on Early Recognition Methods of Cover-Collapse Sinkholes in China

Cover-collapse sinkholes pose a major geohazard occurring in mantled karst regions in the south of China in recent years. Cover deposits generally mask the subsurface development and propagation of the deformation to the topographic surface. Human security and land-use planning in sinkhole-prone areas need to be preceded by detailed investigations focused on identification of pre-existing sinkholes, subsurface dissolution, subsidence features, and groundwater condition. Thefore the abnormal, early hidden danger signs (ground, underground and hydrodynamic) of karst collapse are studied. Further, the corresponding identification techniques and methods are presented, such as surface surveying techniques (satellite remote sensing, the drone, etc.), underground detection technology (ground penetrating radar, microgravity, micro tremor, etc.), and monitoring of groundwater conditions. Finally, all kinds of techniques and methods can be combined to form a comprehensive system for identifying hidden dangers of karst collapse. This paper aims at identifying the early hidden dangers of karst collapse geological disasters. This has important theoretical, technical and social significance in order to minimize the impact of disasters on the people and the environment. Introduction Cover-collapse sinkholes are a major geohazard occurring in soil-covered karst regions. Cover-collapse sinkhole features are the result of the water-borne transport of soil or other related material downward into underlying voids in either the limestone bedrock or the soil profile. Cover deposits generally mask the subsurface development and propagation of the deformation to the topographic surface (Beck, 2004; Waltham et al., 2005; Gutiérrez et al., 2008, 2014). When sinkholes, including sudden catastrophic collapses and subsidence at considerable depths, may adversely interact with the human environment, multidisciplinary approaches should be planned to 1. Ascertain the surface subsidence and sinkhole features; 2. Locate and define precisely the subsurface dissolution and underlying subsidence features (such as karst cave, soil-cavities, the presence of active subsidence and so on); 3. Monitor groundwater conditions. Land-use planning in sinkhole-prone areas needs to be preceded by detailed investigations focused on the identification of pre-existing sinkholes, subsurface dissolution and subsidence features (Galve et al., 2009). Karst collapses have occurred frequently in the south of China in recent years. The present study represents a contribution to monitoring and understanding the genesis and early stage evolution of a sinkhole using different methodologies. Methodology The multidisciplinary approach follows three aspects: 1. Surface surveying methods (field surveys, satellite remote sensing, the drone, etc.); 2. Underground detection methods (ground penetrating radar, Photoelectric monitoring, etc.); and 3. Hydrodynamic monitoring. Surface Survey Methods In some cases, pre-collapse surficial evidence can be identified by topographic depressions and geomorphological analyses. Field surveys and interpretation of remote-sensed imagery are often useful to identify sinkhole surface factors (Forth, et al., 1999; Kaufmann, and Quinif, 2002; Brinkmann, et al., 2007, 2008; Argentieri, et al., 2015). To a certain extent, the remote sensing method can provide the data necessary to guide investigations and monitoring. Thorough reconnaissance of the ground may locate sinkholes not identifiable on aerial photographs, due to their reduced size, depth, or vegetation cover. UAV Remote Sensing In digital photogrammetry, unmanned aerial vehicles (UAV) are a relatively new technology that can be Long Jia Institute of Karst Geology, CAGS,Guilin 541004,China Yan Meng Key Laboratory of Karst Collapse Prevention, CAGS,Guilin 541004,China Zong-Yuan Pan No.50, Qixing Road GuilCity, Guangxi Province, China, jialong@karst.ac.cn