| Guanghua basin is a typical shallow covered karst area in China,which is located in the northern core of the Guangdong-Hong Kong-Macao Greater Bay Area.Sinkhole collapse has become one of the most prominent geological environment problems in the region with the worsening human engineering activities and the extreme climate change in recent years.It is also an urgent geological disaster problem that needs to be solved in the planning and layout of local land space,the construction of major projects and the protection of ecological environment.Five technical theory frame system has been basically formed including genesis mechanism,identification and evaluation,monitoring and early warning,emergency disposal and risk management throughout the domestic and foreign research.But he problems are still not well solved including where is the fall,when collapsed,how to collapse.The prevention and control of sinkhole collapse is still a world-class technical problem in the field of earth science,mainly manifested in the insufficient quantification degree of the causal mechanism,the insufficient precision of the hidden danger identification and evaluation method,simple monitoring method and the difficulty in obtaining the monitoring and early warning threshold.The Erosion-Breaking-Collapse(EBC),Erosion-Suction-Pressing-Fall(ESPF),Penetrating-Flow-Leakage(PFL)and Vibration-Liquefaction-Collapse(VLC)development modes of sinkhole collapse according to the function way,mechanical combination mechanism and forming process based on the analysis of forming geological background,present situation and development,time and space distribution rule of sinkhole collapses in Guanghua basin.Multi-parameter monitoring and early warning research were studied using combination method of the amplitude of ground water level,groundwater flow,groundwater chemical characteristics and groundwater turbidity from the key trigger factors of sinkhole collapse.The relationship between the development of soil cave and the groundwater water chemical characteristics was found and proved.The prediction of sinkhole collapse occurred was realized by the"Abnormal Data Analysis(ADA)".The process and the stage of the development of soil cave was reflected by the ground water turbidity cumulative curve.The comprehensive analysis of these methods to realized the multi-parameter monitoring and early warning by the energy conservation and transforming idea.The results show that the precision and level of early warning for sinkhole collapse are greatly improved in Guanghua basin.It is beneficial to the practical application.The risk prevention and control measures of sinkhole collapse were selected as a key dangerous assessment factor.The land use types and distribution of GDP were used to evaluate the vulnerability.Finally,the prevention and control idea of sinkhole collapse based on the control of safe exploitation of underground water level is put forward.It is very practical and operational.The thesis has the following main understandings:Firstly,the geological conditions of Guanghua basin are very favorable to the development of sinhole collapse,and it is an ideal place for the comprehensive study.The guanghua basin is a shallow-covered karst area,with the highest karst development from minus 35 meters to minus 80 meters in elevation,mainly large and medium-sized karst caves,and the deepest karst development up to 427 meters underground,with abundant karst groundwater.The formation and evolution of sinkhole collapse correspond to the three stages of urban development.More than85%of sinkhole collapses is closely related to human engineering activities such as underground engineering excavation,limestone mining,water source pumping and foundation engineering.The mode of EBC,ESPF,PFLand VLC of sinkhole collapse was built according to the function method,the mechanics mechanism and forming process combination ideas to comprehensive understand trigger factors and formation mechanism of karst collapse in Guanghua basin.It is advantageous for the monitoring,early warning and risk prevention control.Secondly,multi-parameter monitoring can greatly improve the precision and level of karst collapse warning in Guanghua basin.The multi-parameter monitoring and early warning was researched by the combinatory analysis of the amplitude of ground water level,groundwater flow,groundwater chemical characteristics and groundwater turbidity.The results showed that regional soil cave development situation can be reflected by the analysis of groundwater chemical characteristics,the analysis of amplitude of ground water level and groundwater flow can predict the opened time of the sinkhole collapse,and the ground water turbidity monitoring can dynamically reflect the formation and development of sinkhole and it can be used in space and time early warning of sinkhole collapse.The combination of the four methods through the conservation of energy and material transformation can greatly improve the precision and level of s monitoring and early warning of sinkhole collapse,and is beneficial to the practical application.Thirdly,the high risk area of sinkhole collapse in Guanghua basin is significant and the job of risk prevention and control should be strengthened.The risk assessment was compeleted based on the analysis of liability,dangerous and vulnerability,which the interaction between rock and soil water,triggering factors,prevention and control measures,land use type and GDP were select as some key factors.The results show that the high risk area of sinkhole collapse in Guanghua basin is 416.18 km~2,accounting for 58.15%of the total area of limestone rock,mainly distributed in Huadu and Baiyun district of Guangzhou city and Nanhai district of Foshan city.The safe groundwater exploitation in Guanghua basin to prevent karst collapse has a depth of 9 meters,and the diameter of the groundwater prohibited area is 700 meters through the field and laboratory test.The conclusion can macroscopically guide the prevention and control of sinkhole collapse in Guanghua basin.Finally,some measures and suggestions for preventing and controlling sinhole collapse are put forward,such as controlling the water level lowering,changing the pumping method,and demarcating the forbidden area. |
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