Analysis On The Water-rock Interaction Of Stilling Basin Slope Of Nuozhadu Hydropower Station

Effect of water-rock interaction on the process of slope failure in the engineering slope with complex geological conditions is attaching more and more importance.Nuozhadu hydropower station,lies on the middle fiver of the Lancang River,is the fifth one of the eight power stations.The dam made up of center wall moraine is 261.5 meters high with the capability of 5850MW.The spillway flood discharge is number one in the world with the capability of 55860 MW.The left bank slope of stilling basin will be strongly affected by the atomization-rain caused by spillway flood discharge according to the forecast.A lot of water will seep into the slope and react with the rock mass and affect the slope stability.This paper analyzes the slope failure modes based on the engineering geological conditions and rock mass structure.This paper also analyzes the water-rock interaction of the slope through experiments and numerical modeling on the groundwater seepage on the condition of rainfall and atomization-rain.The research results can be obtained as follows:Firstly,the slope is liable to failure in the form of plastic-tip,horizontal push,circular slide and wedge slide based on the analysis on the engineering geological conditions and rock mass structure of the slope.The likely failure part of the slope lies on the top side of the slope with sandstone and mudstone strata.And the slope is liable to failure in the form of plastic-rip and then developing to the form of horizontal push under the atomization-rain.Secondly,choosing the representative rock and soaking them into the water in order to test the change of water content between unaxisial compress strength and shear strength.Results show that the water content is increasing while the unaxisial compress strength and shear strength decrease with the increasing time of soaking. The silt mudstone is most sensitive to water according to the test.The mineral composition of the clay soil is mainly kaoline and goeschwitzite on the basis of field observation and tests on the mineral composition of weak structural surface.It is obvious that water-rock interaction softened rock mass and fissures of the slope.Thirdly,nine rock samples,five kinds of fault clay and one kind of fissure clay of the slope are chosen to test the minerals.Minerals of the rock are mainly quartz, feldspar and calcite,while the clay are chemically made up of S_iO₂,Al₂O₃,Fe₂O₃ and K₂O.There are three chemical reactions between the groundwater and the slope mass based on the analysis,such as ion exchange and sorption,hydrolyze and hydration, chemical deposition,acidic corrosion,and so on.All these have done to decrease physical mechanics of the structure planes and accelerate the rate of slope failure.Fourthly,this paper analyzes the most dangerous faults combination to failure according to the start criterion of horizontal-push landslide from the point view of hydrostatic-pressure effect.Calculating results show that the block of the slope,which is made up of G_222-2as bottom slip face and f_556-1as back tension fracture,is liable to slide as the water height in the back tension fracture reach to 63.15 meters,that's to say,the underground water level at that point is 785.3 meters high.Fifthly,a seep model of the groundwater in the slope about the relationship between underground water level and time of storm rainfall and atomization-rain is established by numerical simulation to analyze the water-rock mechanics effect and stability of the slope.Results of calculating show that the start criterion is to be satisfied if there were both rainstorm and atomization-rain over 200 hours all the time. Then the horizontal-push landslide is to happen.Sixthly,In order to keep the slope safe,measures to isolate the rock from water must be taken besides the reinforcement by means of cables on place of weak interlayer and fault in the middle and upper slope.Measures such as waterproofing and drainage works in the slope are suggested.