Integrated Research For Sinkhole Collapse In Protection Region Ofdatengxia Dam

Sinkholes collapse is a main environmental geological problem and a commom geological hazard around water conservancy projects in karst area. It influences seriously the normal operation of water conservancy projects. At present, the study about the geological hazards mainly concentrated in the earthquake induced by the projects and leakage issue, but aiming at sinkholes collapse less.Maked an example with the protection area of Da Tengxia Dam, a water conservancy project located in strong karst development zone in the middle of Guangxi province, the paper studies sinkholes collapse comprehensively. It has established preliminary research method system for sinkholes collapse. The method system includes some aspects, as follows:Study on the formation conditions. Through on-site investigation, this study analyzes the geological environmental conditions to form sinkholes collapse in the study field, such as the landform, stratum lithology, geological structure, rainfall, water level of Qianjiang River, groundwater types, water petrofabric, relationship among recharge-runoff-discharge, karst development degree, soil properties, water permeability of karst fissure, hydrodynamic changes of groundwater, human activities, et al.Study on the characters. 102 sinkholes collapse were discovered. Based on their data, it analyzes the formation law of space, time, and geological conditions. It also researches the formation factors, such as landform, stratum lithology, geological structure, hydrogeology and human activity. With the process of sinkholes collapse, the study establishes the models to form soil-caves(sinkholes) collapse. Maked the soil-caves as the research object, it analyzes the mechanics principle.Study on the mechanism and hydrodynamic criterions. There are three formation models of soil-caves, the disintegration model in the aeration zone, the erosion model in the phreatic water zone and the hydraulic fracture model in the confined water zone. Three tests are designed for the three models to obtain the groundwater velocity criterion of erosion model, the water content criterion of disintegration model and the anti-permeability strength criterion of hydraulic fracture model.Study on the risk assessment. The risk assessment system is set up by Analytic Hierarchy Process, and it divides the risk zoning map with GIS.Compared the monitoring hydrodynamic data of groundwater with the three model criterions, it evaluates the risk of soil-caves collapse quantitatively. It uses Modflow software to predict the changes of ground water level and flow velocity caused by Da Tengxia Dam operation in order to research the influence to soil-caves collapse.Study on the prevention. With the comprehensive research on sinkholes collapse, the study advises the degree change of water level of Da Tengxia Dam, including the changing range, rising velocity, drorping velocity of dam water lever, and other suggestion, to prevent sinkholes collapse in the study field.