| The study area is located in the transition zone between the Sichuan Basin and the West Sichuan Plateau,and the north-western margin of the ancient land in Kang and Dian.The regional structure belongs to the junction of the three structural belts of the Xianshuihe NW-oriented structural belt,the east-oriented Longmenshan NE-oriented structural belt,and the south-oriented Sichuan-Yunnan SN-oriented structural belt.During the two tectonic cycles of Yangtze and Caledonian,several sets of marine sedimentary carbonate strata of different periods were deposited.The karst phenomenon is generally developed,the groundwater activity is strong,and the regional groundwater system is complex.The proposed Paomashan tunnel passes through different groundwater systems in the study area from southeast to northwest.Therefore,it is of great significance to study the impact of the groundwater system on the construction and environment of the Paomashan area.Based on field survey data and combining previous research results in Paomashan area,this paper refines the aquifer system in the study area horizontally and vertically,and divides the groundwater system according to the runoff-discharge method.Paomashan groundwater is different In-depth groundwater circulation patterns are discussed,based on the groundwater hydrochemical characteristics of the study area,different types of groundwater replenishment and drainage conditions are analyzed,and the impact of project construction on the groundwater system and environment is studied.The main research results of the paper are as follows:（1）There are five types of groundwater in the study area:loose rock pore water,carbonate rock fissure karst water,clastic rock pore fissure water,bedrock fissure water,and fault fracture zone pore fissure water.It is divided into aquifers according to its water-bearing rock formation and water-rich:Sinian Upper Crystal Formation（Z2s）,Silurian Tonghua Formation second and third sections（St2,St3）,Devonian Upper Upper System（D2-3h）,Carboniferous-Permian Xuebaoding Formation（C-Px）,Permian Middle System Sandaoqiao Formation（P2s）;Water Barrier:Sinian Lower System Muzao Group（Z1m）,Upper System Centipede Formation（Z2w）,Silurian Tonghua Formation 1st stage（St1）,Devonian Weiguan Formation 1st stage（Dw1）,2nd stage（Dw2）,Triassic Middle System Zhagshan Formation（T2zg）,Upper System Zagunao Formation（T3z）,Upper Dashibao Formation（P3d）;impermeable rock mass:Jinning-Chengjiang period feldspar granite（γοPt3）,Hercynian intrusive rock-diabase（βμ4）.（2）The main aquifer in the study area is a set of shore-shallow marine carbonate rocks.According to the sedimentary facies and lithology of each aquifer group in the horizontal and vertical directions,the aquifer system in the study area is refined into:The Danian crystal group（Z2s）is divided into three sections from top to bottom,and the third section has the best water-richness.Most of the karst springs in the area are exposed in this section.The burial depth of the entire Sinian gradually increased from south to north,the thickness of the aquifer increased,the content of carbonate rock was higher,and the degree of karst development and water richness were stronger.The"second section"of the Silurian Tonghua Formation is the main aquifer in the area.The section is mainly composed of pure carbonate rocks with strong water-richness,and gradually thickens from northeast to southwest in the area.The Carboniferous is less exposed in the area,but the water richness is stronger.The Permian Sandaoqiao Formation（P2s）is a set of high-purity carbonate rock formations.The formation gradually thickens from north to south.The carbonate It also increased,and the water richness was stronger.（3）According to the different groundwater runoff-discharge methods in the study area,the Paomashan groundwater system is divided into 23 tertiary groundwater systems and 15 tertiary groundwater systems,including 14 karst groundwater with high purity of carbonate rocks system.According to the water storage structure,it is divided into three major water storage structure systems:syncline longitudinal valley,fault zone,carbonate and non-carbonate contact zone;it is divided into karst pipeline water system with rich water volume and water volume according to the water-containing medium and its rich water There are three systems of rich water system of karst caves and general clastic rock fissure water system.The groundwater in Shuangshibanpengpo in the study area belongs to a typical syncline longitudinal valley water storage structure system.The springs at Songjiagou investigated in the field are all exposed on the fault zone and belong to the fault zone water storage structure system.The plateau Haizi-Xingfuqiao release pool is an underground dark river outcropping point,which is divided into carbonate and non-carbonate contact zone water storage structure system.The three karst springs in Qingquan Village are all in the same groundwater system and have the same diameter feature.（4）The groundwater circulation model in the study area shows that the regional groundwater circulation is mainly controlled by topography and groundwater.The groundwater mainly comes from atmospheric precipitation at the first-grade watershed near the SN trend and replenishment by high mountain snowmelt.Shallow groundwater is discharged near streams and springs.The groundwater in the middle and deep layers is circulated in the deep through the Yarra River in the west and the Dadu River in the east as the groundwater discharge base level.（5）According to the water chemistry and isotope analysis in the study area,the results show that most of the water samples in the study area are HCO3-Ca type water,and the rest are HCO3-Ca-Mg type water.The elements in hot springs,cold springs and surface water samples in the study area are quite different,especially in the main cations Ca2+,Mg2+and main anions HCO3-.The difference in TDS indicates that the karst pipelines in the Crystal Formation and Tonghua Formation are relatively strong,and the groundwater runoff time Relatively long,its water-rock action is more sufficient;while the formation of karst pipelines in the Weiguan Formation is relatively weak,the groundwater runoff is rapid and the duration is short,and the water-rock action is relatively weak.Isotope analysis found that the surface water in the study area was mainly distributed along both sides of the global atmospheric precipitation line,indicating that it mainly originated from atmospheric precipitation replenishment.Individual water samples deviated more from atmospheric precipitation and were below the atmospheric precipitation line,indicating its formation process Subject to certain evaporation.（6）The predicted results of the external water pressure and water inflow along the Paomashan Tunnel are:the calculated value of the external water pressure along the entire tunnel is small,most of them are less than 3Mpa,and only the fault zone and karst development stratum are between 3-4Mpa.Under different methods,the predicted value of the tunnel water inflow is not much different.The prediction result of the groundwater dynamics method is 80889m3/d,the railway empirical value is71494m3/d,the groundwater runoff modulus method predicts the total tunnel water inflow is 72580m3/d,and the atmosphere The precipitation infiltration method predicts that the total amount of water inflow in the tunnel is 70079m3/d.According to the actual conditions such as hydrogeology and climatic conditions in the area,the recommended amount of water inflow is 72580m3/d.Considering 1.5 times of this amount during the flood season,the amount of inflow is 108870m3 d.（7）The result of the risk assessment of the entire tunnel is that there are no high-risk areas and 5 sections in the high-risk areas（DK252+534～DK253+117,DK253+117～DK253+200,DK253+290～DK253+348,DK253+348～DK253+523,DK253+743～DK253+974）,there are 9 sections in the medium-risk area,7 sections in the more dangerous area,and 3 sections in the low-risk area.Among them,the high-risk areas are mainly concentrated in the Sinian Crystal Formation（Z2s）,the second member of the Silurian Tonghua Formation（St2）,and the contact zone between the soluble and non-soluble rocks in the tunnel area.By analyzing the underground water system and the karst spring in Qingquan Village through the tunnel,it is determined that the construction of Paomashan Tunnel has almost no impact on the karst spring in Qingquan Village.The tunnel is located in the deep slow flow zone of the groundwater circulation with an impact radius of 1456m Will cause certain environmental impact on the Yarra River. |
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