Characteristic And Risk Assessment Of Karst Collapse In Jinshazhou City, Guangzhou

The Jinshazhou which is located in the center of the future Guangzhou and Foshancity circle, is the important passageway of Guangzhou to Foshan and the South ChinaSea. The surface collapse is one of primary geological disasters in the Jinshazhourecent years, and this condition is becoming more and more frequently when thegroundwater pumping was applied in the passenger railway Wuhan to Guangzhou. Duoto these karst collapse, buildings（roads, houses） appeared deformation and craze, whichis bringing about great losses to the national economy and important influence topeople’s common life.This article focuses on the influence factors and the collapse characteristics in theJinshazhou, at the same time it divides the dangerous degree of different areas in theJinshazhou. The map which is divided can play the role of the foundation fordeveloping planning, land utilization, base installation arrangement, environmentsecurity strategy at the Jinshazhou.According to geological investigation, this article figures out the geologicalenvironment condition of surface collapse and finds out the laws of karst developmentand surface collapse dividing. At the same time, it completely and systematicallyresearches the surface collapse characteristics and analyses the influence of collapsetopography and geomorphology, formation lithology, geological structure, thedevelopment degree of karst and soil cave, groundwater, human engineering activity.The results indicated that the development degree of karst and soil cave is controlled bybase rock and geological structure. The karst and soil cave is basically growing in themedium and heavy layered limestone of Shidengzi petrofabric （C₁ds）, Hutianpetrofabric （C2+3ht） and sides of fault zones. Through checking drillings in the studyarea, thereare444holes ofkarst than82ofsoil cave,thenwecanfindthatit’s not direct proportion between karst to soil cave. There are only18holes which developed karstamong the82holes, so karst is not the only one way to engender soil cave. Thedevelopment of soil cave can have different control factors. On the other side, we noticethat it is the main factor of surface collapse that groundwater pumping was applied inthe passenger railway Wuhan to Guangzhou. It started with applying groundwaterpumping and ended with stopping groundwater pumping. Collapse has obvious spatialdistribution features, developing from the near to the distant with expanding of thegroundwater hopper which was in the center of1#pumping drilling.First of all, this article chooses primary factors which can influence karst collapse,the conditions of karst developing （liner karst rate, geological structure, types of karst）groundwater dynamic condition （hydraulic gradient, the distance of water level to baserock, groundwater level, the distance of hopper center）, overburden condition （the soillevel structure, the soil level thickness）, within these3conditions and8factors buildingthe system of dangerous areas evaluation. Then using MODFLOW imitates the changeof groundwater flow field in time and space in the condition of pumping output3500m³/d and2000m³/d in the passenger railway Wuhan to Guangzhou and gets thehydraulic gradient and the distance of water level to base rock in the two conditions.Through infiltration and deformation test gets critical hydraulic gradient, we canachieve the evaluation criteria of hydraulic gradient in different areas. In the end,applying ArcGIS to deal with the point files by space interpolation methods （includingTyson gridding method, the distance weighted average method, common Krygermethod） and produce area files to evaluate. According to this system, the dangerousdegree of surface collapse can devide to be4, basically stable, second unstable, stable,extremely unstable. Through the dangerous areas comprehensive evaluation map（pumping output2000m³/d）, the basically stable area takes up52.04percentagewhich is located in the south and southeast of the Jinshazhou; the second unstable areaaccounts for22.27percentage in the north and middle area; the percentage of extremelyunstable is19.80and these areas distributed in Getian,Wunong, Yongdeng,Fengzhou;the unstable areas located densely populated areas （the new communities, Jinshazhoumiddle school, Shafeng village, Xunfengxuvillage）,karst strong developmentareas（Shidengzi petrofabric （C₁ds））,along with fault, takes up5.92percentage of thewhole region. The basically stable areas are nearly impossible to collapse, which can asthe first selection when municipal office and urban construction make planning. On thecontrary, the extremely unstable areas are very easy to collapse. Unfortunately, these areas usually contain a large number of people and economy is booming. Municipaloffice and urban construction should play more attention to prevent and dispose theseareas possible collapse and reasonably adjust exploitation arrangement of groundwater,in case of appearing worse result.