Study On The Influence Of Weak Aquifer In Thick Overburden Dam Base On Seepage Field And Stress Field Study On The Influence Of Weak Aquifer In Thick Overburden Dam Base On Seepage Field And Stress Field

The deep overburden dam foundation with strong and weak layers is always met in Southwest and Northwest China,with the rapid development of hydropower cause,many hydraulic engineerings were built on this foundation.The anti-seepage projects of deep overburden dam foundation have a series of problems,such as great difficulty in construction,long construction period and a large quantity of engineering quantity,which needs to be solved.Weak aquifer frequently exist in thick overburden dam foundation,such as Daga hydropower station,Shangjiang dam and Yingliangbao hydropower station.Whether to take it as base layer of seepage control or to overlook its anti-seepage effect,has a certain effect on cost and progress of anti-seepage project.Fluid-solid coupling can factually reflect the influence of weak aquifer on seepage field and stress fields.This paper is based on the Biot consolidation theory,combined with the nonlinear rheological theory of soil,particularly considering dynamic varying relationship between geo-mechanics parameters and hydraulic parameters,carring out two fields coupled solution by ADINA and GeoStudio,and analyze the influence of weak aquifer in dam base on seepage field,stress field and stress-strain of weak aquifer.And Shangjiang dam calculation model was set up,and discusses whether weak aquifer in deep dam foundation can be used as anti-seepage supporting layer.In addition,analyze the influence of weak aquifer on seepage field and stress field,to verify accuracy of numerical simulation.This paper draws several main onclusions:(1)United seepage control of weak aquifer and cutoff wall can significantly improve the anti-seepage effect of vertical cutoff wall,and effect of semi-closed cutoff wall is greatly superior to suspended cutoff wall.(2)The best depth of vertical cutoff wall is depth that cutoff wall is embedded 2-3 m in weak aquifer on dual structure of thick overburden layer.When cutoff wall is going to embedding in weak aquifer,seepage gradient at the bottom of cutoff wall steep rise,and it should be paid enough attention to project.(3)When the cutoff wall is not set or buried depth of weak aquifer is smaller,the seepage discharge and seepage gradient is smaller.If buried depth of weak aquifer is bigger,the circumstance is harm to the dam.(4)When cutoff wall is set in thick overburden layer,the bigger depth of closed-end combined seepage system which is combined by the vertical cutoff wall and weak aquifer can more effectively reduce the discharge and seepage gradient than the smaller.(5)Weak aquifer and cutoff wall can constitute united impervious system,which can take outstanding effect of water insulation.Principal stresses and strains of petrofabric under weak aquifer reduced,but principal stresses and plastic strains of petrofabric and cutoff wall increased.(6)In Shangjiang dam engineering,seepage discharge and exit gradient of dam base are lower than their allowable value when the semi-closed cutoff wall is adopted,and stress-strain of semi-closed cutoff wall is lower than allowable value,the depth of cutoff wall exampled is 60 m lower than closed-end cutoff wall,engineering quantity can be reduced greatly if the scheme can be adopted.Therefore,if there is weak aquifer in dam foundation,it should be paid sufficient attention to.It can get twice the result with half the effort if weak aquifer can be used after scientific demonstration.The research results can provide a number of theoretical references and suggestions for similar projects,so as to reduce engineering quantity.