Research On Seepage Stability And Seepage Control Design In Jiangxiong Reservoir Dam In Gongga County In Tibet

After the reservoir impounded, a part of water seepages towarddownstream through pervious rock stratum due to the hydraulic pressure headbetween upstream and downstream. If the permeability is too big, theimpounded water in the reservoir will leak a lot. That will impact the economybenefit of the reservoir engineering. If the seepage gradient is bigger than theallow gradient of the layers, the dam and dam foundation will come intoseepage deformation such as piping or soil flowing. Severe seepagedeformation can lead to accident as dam burst, induce uncountable loss of lifeand possession. So, seepage control and seepage stability analysis is importantsubject in rock and soil dam engineering.The paper detailed analyzes the engineering geology condition and thehydrologic geology condition, makes clear the seepage structure and seepageorderliness of the dam area, and based on this builds the three-dimensionalseepage model, uses the Visual MODFLOW to numerical simulate theunderground water seepage and analyze the seepage stability with differentseepage control condition. The main achievement as follows:(1) The geology structure in JiangXiong reservoir is complicated. Theseepage mediums have characters as big thickness, multi layers, and so on.And the head difference between upstream and downstream is big. Seepage bypass the dam and seepage in the base of dam exists simultaneous. Theseepage's three-dimensional character is obviously. For factually simulate theseepage flow field in the dam area, the three-dimensional seepage numericalsimulation research must be taken.(2) The hydrologic geology concept model is built. The seepage mediumin the whole research area is generalized into heterogeneous isotropic phreaticaquifer system. The seepage is laminar, accord with the Darcy's law. The paperuses the steady seepage theory to calculate. Quaternary alluvial-proluvial massis generalized as pore seepage mediator;bedrock strong weathered layer isgeneralized as equivalent continuous mediator;bedrock weakly weatheredlayer is generalized as crevice network discrete seepage mediator;man-madeseepage mediator as dam and impermeable structure is generalized as poreseepage mediator.(3)The paper deeply researched the seepage structure and the seepageorderliness of the soil and rock mass in the research area. Considered theseepage mediator in research area contains pore seepage mediator, equivalentcontinuous mediator and crevice network discrete seepage mediator. Whenpreset the permeability coefficient, quaternary alluvial-proluvial mass andbedrock strong weathered layer is according to the site experiment outputs,man-made seepage mediator is according to the hydraulic design parameter,and bedrock weakly weathered layer is according to the crevice rock masspermeability tensor theory.(4) Considering the geology engineering condition of research area andthe mature experience of other reservoir engineering in Tibet, the paperchooses the geotechnical membrane core earth and stone dam, concreteunderground continuous wall, associated with grout curtain. According to thegeology examination and the exploration datum, with the principle of safe,economic and logical, the paper designed three seepage control design scheme,associated with three conditions of beneficial water height, design water heightand check water height, separately simulated and calculated in thethree-dimensional seepage model. Then the output of seepage discharge, flowfield, and maximum hydraulic gradient in different conditions is got.(5) As see in the three-dimensional seepage calculation output, thedischarge per unit width of river valley and left dam abutment is comparativebig. So seepage break may happen in this area. According to the synthesisanalysis discrimination method of China institute of water resources andhydropower research, the paper calculate the allowed gradient of river valleyand left dam abutment. After judged, all the seepage control schemes can meetthe request of seepage stability. The seepage deformation is inexistence.(6) The paper separately compares and analyses the three seepage controlscheme in aspect of seepage discharge, seepage gradient, and economic.Among the three seepage control scheme, the seepage discharge and seepagegradient of seepage control scheme 3 is the least. And the seepage controlscheme 3 can reduce the engineering invest. So, the seepage control scheme 3is determined as the best design scheme.(7) The Visual MODLOW of three-dimensional seepage numericalcalculation program which is based on the finite difference calculus, now isbecome the standard specialty software system in the international, with it'scharacteristics such as visualization, systematization, and strong numericalsimulation function. The paper uses the Visual MODFLOW in thethree-dimensional seepage simulation and seepage control design optimization,solves the practical problem in engineering very well, and got a good effect.