Research On Karst Growth Law And Foundation Stabilityof Some Major Project In Guizhou Province

A major project locates in southwest Guizhou Plateau, which crosses multiples of hydrological and engineering geological units.DevelopedKarst worsened the site’sgeologic conditions,which hasbecome the main engineering geological problems that limited engineering construction.Research on karst’s characteristics, regularity and mechanism, evaluation ofits foundation stability and influence on engineering,is veryimportant for engineering construction.In this paper, on the basis of fully collecting predecessors’ research achievements in karst, through the large scale engineering geological mapping, geophysical prospecting, drilling, physical and mechanical experiment of rock mass, semi-quantitative analysis, FLAC numerical simulation, risk assessment based on GIS, etc., I had systematically researched karst’s development characteristics and distribution, development mechanism, the stability of karst foundation and the risk of karst collapse, explored the prediction effect by geographic information system on karst collapse, mainly made the following conclusions:(1)The terrainis complex in this field area, which is mainly denudation-erosion shallow hill and denudation-erosion middle hill, belongs to the regional level Ⅱ planation surface with a relatively good regional stability.(2) The karst’s development on the ground surface is strong, including 152 surfacekarst with 28 karst funnels, 44 sinkholes, 22 karst pits, 36 karst depression, 22 soil caves, and lots of Clint and karren grooves;Underground karst in this area mainly contains karst erosion fracture zone, dissolved gaps and small caves.(3)The trend of karst groovesin this area is almost the same as the one of carbonate rocks’ joint surface and stratas,which is NNE to NE direction;the long axis of Karst depressions, karst funnels andsinkholes often indicate the trend of rock layers and joint surfaces or the direction of the structure line,which isNNE to NE and nearly south to north;Vast majority of the caves are less than 2meters’ tall above the revealled karst caves,which accounted for 64%;While there are 7 caves taller than 5m, and the largest one is 13.3m.In the field area, exploration proved underground cavesare mainlyin a vertical form;There are horizontally developedkarst cave in the depressions, or at the bottom of karst funnels, but generally in a smaller scale.(4) Controlling factors of karst development in the area are mainly stratigraphic lithology, neotectonic movement, geological structure, hydrogeological conditions.The stratum’directionis northwest, which is monoclinal structure trend to northeast, and the lithology is mainly limestone;The carbonate rocks in the field area is given priority to with micro to fine grainstructure.Above the base level of erosion,the karst is maialy developped vertically, and horizontally near the base level of erosion Nearly vertical joints of rock mass in the areaarerelatively developed well,and the permeability is alse good.The development of karst in the field area are mainly controlled by the shallow bedrock fissure water that runoffshorizontally near the base level of erosion.(5) There are 22 collapsed soil caves in this area, and engineering geological drilling exposed one another soil cave.All the soil cavesare small in size, and distributed within all of the soluble layers,whoseshapeare mainly controlled by the northeast-trendingextension joint and caused by surface water’sdownward erosion.,and now is at a stable state.(6) The qualitative evaluation results show that the stability of karst cave is relatively good under the natural state, the possibility of collapse islow;Semi-quantitative evaluation method based on specification determined21 unstable caves,which accounted for 8.75%, showing that stability of karst caves in the area is relatively good and for engineering construction.(7)This paper used the FLAC3 D software to numerically simulate the stress, strain and displacement of surrounding rock of three dimensional cave after filling,and the governance effect after roof-crossing and grouting.The result shows that grouting effect is obviously better than roof-crossing method for the karst caves with thickoverlying clay layers,especially in the aspect of improving the effect of stress distribution.But the effect of grouting treatment to reduce subsidence and plastic zone distribution is limited.(8) By using ArcGis software’s parameters marking, weighted sum method, this paper achieves the prediction evaluation of karst collapse’ risk, dividing the field area intofour grades’ danger zone by the.risk of collapse.Predicted results verify the feasibility of GIS technology in the risk evaluation of karst collapseand the validity of the selected model and indicators in this project.