Study On The Seismic Dynamic Characteristics Of Tailings Dam With Lens

Tailing pond is a major hazard source of artificial debris flow with high potential energy.In the last few decades,there are many dam-break accidents because of earthquake which not only can cause serious life and property loss for the people living in the downstream,but also can impact on the surrounding environment.In China,more than 95% of tailings ponds are constructed by upstream method?but in the process of upstream dam construction,it is easy to produce some different number and size lens in the fill dam,which has a serious influence on the stability of dam under earthquake condition.Based on the theory of earthquake dynamics,the stability of the tailings dam with different quantity of lens is studied by means of model test,theoretical analysis and numerical calculation in this paper,the results show as follows:(1)The mechanical properties of the tailings with different number of lens are obtained by indoor test.For conventional tailings,the internal friction angle decreases and the cohesion increases with the decrease of particle size.For the tailings containing lens,the cohesion increases with the increase of the lens inter layer,and the internal friction angle of medium tailings and fine tailings gradually decreases.Through the micro analysis of tailings,it can be seen that the tailings sand diameter increases,the pore size increases and the porosity increases,then the permeability of tailings increases.(2)Through the calculation of the seepage characteristics of the tailings dam under earthquake condition,it can be seen that the phreatic line of the tailings dam without lens is generally a smooth curve.The phreatic line of the tailings dam with lens uplift when lens are distribute in the top of the phreatic line or the lower part near the phreatic line.The phreatic line which the lens are distributed in the lower part of the dam is higher than that in the upper and lower parts,the lens which are distribute in other regional can affect the horizontal and vertical seepage velocity in the vicinity of the region.Under the earthquake condition,the phreatic line intersect at and overflow in the middle and lower reaches of the fill dam and slope.When the lens is generated at the lower and upper position of the dam and the area of the lens is increased,the water level line overflows in the middle and lower reaches of the dam slope.(3)Through the simulation of the stability of tailings dam under the earthquake condition,the following conclusions are drawn.When the lens is not taken into account,the dam is in a safe state.Under normal and seismic conditions,the safety factor of dam gradually decreases from the upper to the lower of the dam;When the lens appear the upper,middle and lower parts of the dam at once,the minimum safety factor can be got.With the increase of the length,thickness and area of the lens,the safety factor of the dam will be reduced.(4)Through the indoor seismic model of tailings pond,the top of tailing pond is first of all to have cracks in earthquake condition,cracks expand with the continuous earthquake time.But in the whole process of earthquake,the degree of damage is obvious in the downstream of dam.