| The land area of China is about 1/3 as a soluble rock cover area.Due to the rapid urbanization process in recent years,the construction of the project has to be extended to the karst area because of the sharp contradiction between human and land,and the construction of the project is restricted by the subsidence and subsidence.The lake area is located in Nanan District of Chongqing area,population density,economic activity.In order to improve the indoor traffic conditions,there are continuous construction of large tunnel projects in the area,on the one hand,it improves the regional traffic conditions,on the other hand,it also makes the regional collapse of the mainland constantly.In this paper,the geological survey and data collection of karst development and collapse in the region of Tu Shan Lake are investigated.The characteristics of karst development and collapse in the study area are revealed by means of geophysical prospecting and drilling,and the collapse force and collapse force of the collapse bodies in different periods are analyzed by the related knowledge of statics and soil mechanics.The collapse formation mechanism of the study area is revealed,and 12 factors such as geological structure,topography,cover layer,hidden karst development and groundwater hydrological condition are selected,and the karst development assessment model is constructed to subarea the risk grade of collapse in the study area,and the risk grade of karst collapse in the area is drawn.It can provide some references for subsequent governance and engineering planning.The main research results of this paper are as follows:(1)Through the collection of data,hydrogeological survey,geophysical prospecting and drilling,the characteristics of the geological environment and the hydrological environment of the groundwater are revealed.It shows that the development of karst is gradually reduced from the nucleus of the anticline to the two wings and is distributed in a bead like distribution along the direction of the river in the dark river,and has been studied by the comparison and analysis of geophysical prospecting and drilling.In the study area,7 areas of karst development are developed.The area is the dense distribution area of hidden karst and collapse,which is the main infiltration channel of surface water.The calculation and analysis of the data obtained by the pumping test show that the numerical value of the permeability system calculated by the study area is far greater than the empirical value of the permeability coefficient measured in the laboratory.The upper part of the study area is fractured and the groundwater is draining down vertically.(2)Through field investigation,the distribution of regional tunnel is clarified,and the groundwater recharge of the study area is calculated by using the change of water inflow chart of the tunnel and the groundwater recharge in the study area,and the main reason for the leakage of groundwater in the Nanshan tunnel is determined,and the influence range of the groundwater leakage is defined according to the scope of the funnel and the distribution of the soluble rock.The distance between the over ground water funnel and the original groundwater delineated the grade map of the leakage strength of the groundwater.According to the data collected and the results of the hydrology investigation,the distance between the ground water and the base rock surface,the variation of the groundwater level and the effect of the underground water funnel on the collapse were systematically studied.And the hydrological and environmental characteristics of the groundwater are delineated the three factors.(3)According to the geological survey,the data of the subsidence distribution,formation time and plane size are statistically analyzed.Through the data analysis,it is revealed that the formation law of karst collapse is developed in the form of collapse group and synchronously deepens with the precipitation period.Two types of collapse are determined according to the characteristics of the synchronous response to the precipitation period,and the differences in the collapse force and the anti collapse force of the two types of collapse are analyzed by using the related subject knowledge of statics and soil mechanics.It is revealed that the formation mechanism of the subsidence in the study area is different in different periods,that is,the non rainfall period.The mechanism of collapse is vacuum suction mechanism,and the formation mechanism of rainfall period is the mechanism of submarine collapse.(4)According to the results of geological survey and laboratory research,the influence factors of 12 karst collapses,such as bedrock,karst development,topography,geological structure,thickness of cover layer,groundwater and geotechnical interface,are determined.The karst collapse in the study area is constructed by analytic hierarchy process,grey relation analysis and set pair theory.The risk assessment system has partitioned the risk grade of the collapse through the relationship between the degree of opposition,the degree of difference and the size ranking of the same degree.The ArcGIS platform was used to draw the hazard zoning map of the study area,and the reliability was verified by the number of regional collapse points,and the results were verified.It can provide some references for subsequent engineering management and future engineering planning.(5)According to the research results and management experience of the Nanshan mountains and Lakes region and the related areas,the tunnel water gushing and rainfall infiltration are the inducing factors of karst collapse.Based on this kind of experience,some suggestions on the process of tunnel planning and construction are put forward. |
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