Research On Multi-layered Complex Karst Water System And Reservoir Anti-seepage In Heitanhe Reservoir

The Heitanhe Reservoir is located in the original area of the Eastern Yunnan Mountain.In the area,the non-soluble rocks of the Lower Permian Liangshan Formation with uneven thickness are developed between the soluble rocks of the Lower Permian Qixia and Maokou Formations and the Upper Carboniferous Maping Formation.The upper stack is combined to form a double-layer aquifer structure.Fold uplifting,fault cutting and the change of stratum thickness of the Liangshan Formation will cause communication and connection of double-layer water-bearing systems in some areas,forming complex multi-layer karst water system.In space,the appearance of the double aquifer is gentle,the thickness of rock changes greatly,and the development of karst is extremely uneven.When reservoir is increased in capacity,reservoir water may leak out of reservoir along the double-layer aquifer karst medium and fissure medium,which in turn affects the economic benefits of reservoir project.The engineering geological problems of reservoir karst leakage under the control of double-layer karst water system are complicated,which makes reservoir anti-seepage difficult.Therefore,in-depth study of the impact of the double-layer karst water system on reservoir leakage can not only analyze reservoir leakage problem,but also provide a basis for the reservoir anti-seepage design.This article analyzes karst development characteristics of the double-layer aquifer in the area,and identify the spatial structure and distribution characteristics of the multi-layer karst aquifer under the control of the Liangshan Formation insoluble rock and fault structure,and the characteristics of karst water flow,and further study the leakage problem of reservoir in the double-layer complex karst water system,and propose a suitable anti-seepage scheme;A three-dimensional numerical model is used to simulate and analyze the characteristics of the seepage field and the amount of leakage of the reservoir under natural,impounded and impervious conditions.The feasibility evaluation of the impervious scheme is carried out,and the optimal design scheme of the impervious reservoir project is proposed.Mainly obtain the following knowledge:?1?The soluble rocks of the Lower Permian Qixia Formation and Maokou Formation and the Upper Carboniferous Maping Formation in the study area were blocked by the Lower Permian Liangshan Formation insoluble rocks,forming a double-layer karst aquifer structure.The Qixia Formation and Maokou Formation are the dominant karst development strata in the area,and the development degree of karst and the permeability of the rock mass are stronger than the soluble rocks of the Maping Formation.The drilling reveals that the development of karst has vertical dissolution and zoning.The karst strength above 1940m elevation is developed,and the rock mass is mainly of medium permeability;The karst is moderately developed between1900?1940m elevation;the erosion phenomenon of the rock mass below 1900m elevation disappears and the karst is weakly developed..?2?The insoluble rock of the Liangshan Formation is continuous and reliable in thickness in most areas.The two aquifers constitute two independent karst aquifer systems,and two layers of groundwater run off in layers along the karst medium.In the Nine Caves-Lingjiaotang F₃,F₁₁and F₁₂fault development areas,water-separation restriction of the Liangshan Formation was cut and destroyed,and the two aquifers were connected to establish hydraulic connection.,and formed a complex double-layer karst water system.There is a natural watershed on the right bank of the Qixia Formation and Maokou Formation to separate the reservoir from the Lingjiaotang underground water table.The groundwater level of the Maping Formation is low and has certain pressure bearing capacity.The hydrodynamic conditions are similar to the Qixia Formation and Maokou Formation.The double-layer karst water is supplied by precipitation.Under the action of faults,fissures,karsts and other water conduction,groundwater is mainly runoff along the layer,and it is collected into the Bage cave in the lower reaches of the Heitan River and discharged to the Niulan River through the dark river pipeline.?3?Analysis and evaluation of reservoir leakage in double-layer karst water system:The reservoir is controlled by a multi-layer karst water system,after reservoir is increased in capacity,the right bank Shuipingping-Jiudong reservoir section is the main leakage section.The reservoir water will seep through the aquifer karst medium of the Qixia Formation and Maokou Formation,the junction of the double-layer aquifer and the fault to the west of Lingjiaotang low adjacent valley,aquifers of the Qixia Formation and Maokou Formation are the main leakage rock masses,which are the leakage of fractured and dissolved rock masses.The numerical simulation analysis seepage field in reservoir area show that:The distribution form of the natural seepage field and other water level lines in reservoir area is generally consistent with topography and landform changes.The groundwater as a whole runs from east to west,with small circulations throughout the reservoir area;After reservoir is impounded,the natural groundwater divider disappears,the groundwater seepage capacity is enhanced,and there is obviously a hydrodynamic condition of runoff in the direction of the lower adjacent valley of Lingjiaotang.?4?According to the potential leakage problem of reservoir leakage section in the double-layer karst water system,three anti-seepage schemes were designed.Along reservoir leakage direction,it is divided into the upper Qixia Formation and Maokou Formation rock leakage sections,the downstream Qixia Formation,Maokou Formation rock and Maping Formation rock leakage sections and reservoir area F₃fault leakage section.The anti-seepage line is arranged in the seepage section of the Qixia and Maokou formations in the upstream of the reservoir water leakage direction and the F₃fault leakage section.The depth of anti-seepage deepened after the group.Curtain depth of each scheme:55m,85m,105m,155m.The numerical simulation results of the anti-seepage scheme show that:When there is no anti-seepage curtain,the leakage in reservoir area is 83543m³/d,which is a serious leakage;under the anti-seepage curtain condition,the maximum leakage in reservoir area is curtain depth of 55m in the scheme1,and the leakage is 61358m³/d,the minimum is curtain depth of 155m in scheme 1,the leakage is 5678m³/d.Under different curtain,as the curtain depth increases,the amount of leakage decreases,the more obvious curtain water blocking effect,reservoir area changes from severe leakage to slight leakage.?5?According to the economics and risks of each anti-seepage scheme,the feasibility evaluation of the anti-seepage scheme is carried out.It is considered that when the curtain depth is 105m,the economic loss and cost investment are more reasonable,and the leakage risk is less.Compared with other schemes,scheme 2 has the shortest distance of key anti-seepage planes,economic loss and cost investment are relatively small,and at a curtain depth of 105m,the leakage volume is 10906m³/d,and the leakage volume reduction can reach 87.12%it is a slight leak.Therefore,it is recommended to choose the second anti-seepage line.Curtain depth is recommended to 105m below the ground,accounting for 70%thickness of the leakage rock?P₁q+m?.