Study On Formation Mechanism And Application Of Coastal Karst Ground Collapse

Karst geology is widely distributed in China,and karst ground collapse disasters are serious,especially in coastal karst areas.Karst ground collapse is easily induced in the process of mining resources exploitation,underground space utilization and various facilities construction,which seriously threatens the safety of people’s lives and property.Based on the water control project of Guangxi Huarun Cement(Hepu)limestone mine,which is surrounded by the sea on three sides,this paper studies the formation mechanism of karst ground collapse of different geological structures under tidal action according to the development characteristics of coastal karst and hydrogeological conditions of the mine.This paper generalized the binhai karst collapse under different geological structure model,analyzing the binhai karst ground under tidal mechanics characteristics of karst collapse,by means of combining field laboratory test and numerical simulation,and get the process of subsidence and subsidence under different geological structure form,the typical stages in the development of the soil hole the key influence factors and development trend,According to the engineering site,the prevention and control measures of karst ground collapse are put forward.The main research contents and achievements of this paper are as follows:(1)Analysis of mechanical characteristics of tidal action,on the basis of the structure of the overlaying soil is generalized the tidal type under the action of single permeable layers,single layer resistance under water type,double layers on through resistance,resistance under fully on the double 4 kind of karst collapse mode,analysis the corresponding littoral karst ground collapse law of geological structure,further of littoral karst ground collapse under the typical geological structure is analyzed with mechanics,The stability coefficient of cap layer is proposed.(2)Independently developed a test system to simulate the collapse of coastal karst ground,and carried out experimental research on the collapse of coastal karst ground with different geological structures.By analyzing the changes of pore water pressure and soil displacement under different geological structures,the collapse shapes of soil caves with different geological structures are obtained:single permeable soil layer is funnel-shaped soil tunnel,single waterresistant soil layer is altar soil tunnel,upper and lower permeable soil layer and upper and lower permeable soil layer are disc soil caves.The ground collapse mechanism of different geological structures under tidal action is revealed.The experiment shows that tidal action intensifies the occurrence of karst ground collapse in coastal area.(3)FLAC3D numerical simulation software is used to study the influence of tidal action on the collapse of coastal karst ground,and the key influencing factors,weak position of soil and the collapse trend of soil cave in different collapse stages are obtained.At high tide,the maximum shear stress is distributed in the arch foot and the arch position,and the shear stress at the roof tends to increase,and the soil tunnel is in a more unstable state.At ebb tide,the soil mass above the karst opening is relatively weak due to the effect of gravity and pore water pressure difference.The arch foot of the soil cave is located at the shear stress concentration,and the displacement of the arch foot and vault is large,and the soil cave tends to increase.The results show that tidal action increases the load and instability of soil cave,and accelerates the failure process of soil cave,which is consistent with the collapse process of laboratory test,and further reveals the mechanism of ground collapse under tidal action.(4)In view of the characteristics of karst ground collapse in the coastal area of Guangxi China Resources Cement(Hepu)limestone mine,the groundwater dynamic conditions are more complicated under the influence of tidal action and mining,and the collapse is mostly concentrated in the runoff zone.The key passage of groundwater was identified by geophysical drilling,the discontinuous curtain was formed by grouting to intercept the flow,the collapse pit was backfilled with grouting,and other prevention and control measures were put forward.Good economic and social benefits have been achieved in the field application,which provides theoretical and technical reference for the treatment of coastal karst ground collapse under similar conditions.