| Jia jiaoshan anticline is located in the northeastern margin of the Sichuan Basin and belongs to a part of the parallel ridge valley in the east of Sichuan.Its trend is northeast-southwest,forming a continuous arc-shaped mountain about 75km long.There is no large river valley cut into soluble rock in the area,which is a complete fold area.The holding of soluble rock strata in the non-soluble rock strata in the area formed a relatively independent water-soluble system of soluble rocks.During the construction of the parallel ridge valley tunnel project in eastern Sichuan,different levels of karst water inrush disasters were encountered,which affected the groundwater environment to varying degrees.In the plan for the construction of the Chengdu-Dazhou-Wanzhou High-speed Railway tunnel project,from the perspective of project economic benefits,the straight-through false angle mountain scheme should be the optimal line position,but the karst strong development through the false angle mountain anticline mountain section is prone to tunnel water inrush Disasters and a series of environmental and geological problems;if a bypass to avoid a large area of soluble rock is adopted,the length of the line position will increase accordingly,thereby increasing the investment cost of the project and reducing the economic benefit of the project.This paper seeks to find an optimal line position with suitable line length and little impact on groundwater environment,to provide scientific and objective theoretical support for the site selection of the high-speed railway tunnel through the false angle anticline.This paper is based on the practice of high-speed railway construction in karst areas,combined with field hydrogeological survey,to summarize and analyze the karst development characteristics,influencing factors and groundwater circulation patterns of the pseudo-horn mountain anticline,from the development density of horizontal cut valleys,spring development density and karst depression development density Equal indicators divide the development intensity of karst.Using GMS-Modflow software to analyze the inversion of the groundwater natural flow field in the Jiaojiao Mountain Anticline,it is planned to predict and analyze the groundwater seepage field and environmental impact after the tunnel construction of the proposed Chengdu-Dazhou-Wanzhou high-speed railway Jiajiaoshan Tunnel at different positions.The research seeks to optimize the route selection scheme of the tunnel project construction with little impact on the groundwater environment and low project investment.The main research results are as follows:?1?The soluble rock in the study area accounts for 35.9%of the total area of the anticline mountain.The large-area exposed soluble rock has strong water richness,which is conducive to the development of karst.The soluble rock aquifers in the area are the Lower Triassic Jialingjiang Formation?T1j?,the Middle Tectonic Badong Formation?T2b1?and the Badong Third Member?T2b3?.And karst cave water in the cracks of clastic rock carbonate.Among them,the Jialingjiang Formation?T1j?and Badong Formation 1?T2b1?have strong water-richness and are the main aquifers,and the Badong Formation Third Member?T2b3?have moderate to strong water-richness,and are the secondary aquifers.?2?From the perspective of groundwater system theory,the groundwater circulation pattern of the Jiajiaoshan anticline is divided.The groundwater circulation in the Jiaojiao Mountain area is mainly controlled by lateral valleys,and the discharge bases at different elevations control different groundwater circulation patterns.Shallow-cut gully excretion on the side.The first-level karst water system of the Jiaojiao anticline is divided into two second-level karst water systems.The second-level karst water system is the karst water subsystem of the Jialingjiang Formation and the third-stage karst water subsystem of the Badong Formation.?3?Analyze the factors controlling the development of karst by means of statistics:development density of cross-cut valleys,development density index of spring points,development density of karst depressions,according to the development density of cross-cut valleys,development density of spring points and development density of karst depressions According to various indicators,the pseudo-horn mountain anticline is divided into three sections.The north part of the T2b1 is the most developed within 20km southward,with a moderate development between 20 and40km,and the smallest development between 40 and 50km.Mathematical theory divides the study area into three sections according to karst development intensity:the north section?Maoba-Beipaigou?is a karst strong development area,the middle section?Daya Village-Maoba?is a karst medium development area,and the south section?Taojia?Dam-Daya Village)is a weakly developed karst area.?4?According to the strength of karst development under the control of the groundwater circulation model,a hydrogeological model of the pseudo-horn mountain anticline was established.The simulation of the groundwater seepage field across the three proposed tunnel lines with different karst development strengths across the anticline mountain was perpendicular to the stratum in the study area.A total of sections are arranged in the range,and boreholes are arranged on the section lines to read the elevation of each rock layer,statistically organize the elevation data,use GMS-Modflow software to describe the three-dimensional hydrogeological model,input the boundary and initial conditions into the model,and import the field survey spring points and exploration boreholes The model was identified and verified,and then the natural flow field in the study area was reversed.The results showed that the head distribution of the natural seepage field was mainly controlled by stratigraphic changes and topography.The head value in the southwest is high,which is the groundwater recharge area,and the head value in the northeast Gradually decreases.Based on the natural seepage field model,after describing the construction of the tunnel A and B schemes with different karst development degrees,the conceptual model of the groundwater seepage field under the disturbance of the groundwater environment,the simulation results show that the impact on the groundwater gradually increases after the tunnel construction,and the maximum drawdown It can reach 100?200m,and the influence range is about 3?4km on both sides of the tunnel and the flow of some springs have attenuated or dried up flow.Then,the underground tunnel seepage field was simulated for the encrypted tunnel scheme 1#?5#?the tunnel group is laid out from A to south roughly according to one tunnel scheme every 5km?,and the simulation results show that at the inclination end of the first section of the Badong Formation,it is more In other words,the water influx of the 2#tunnel is39011.6m3/d,which is reduced by one-half,the impact range is about 1km,and it is reduced by two-thirds.The length of the Dazhou-Wanzhou tunnel line is only increased by 7km.The impact is small and it meets the requirements of economic benefits.Therefore,the location of the high-speed railway tunnel passing through the Jiaojiao Anticline should be selected near Wutong Temple,which is about 15km away from Scheme A. |
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