| Tailings pond is a dangerous man-made debris flow source with high potential energy.Once the dam is breached,it will not only flood and destroy the downstream living and production facilities,but also cause serious environmental pollution.At present,there are about 8000 tailings ponds in China,more than 80% of which are constructed by upstream method.The upstream tailings dam has the lowest operating cost,but its seismic performance is poor.China is located between the world's two major seismic belts(the Circum-pacific seismic belt and the Eurasian seismic belt).According to the statistical results of tailings pond accidents,seismic liquefaction is the second major factor causing the accidents of tailings pond.The safety production situation of tailings pond in China is very serious.How to alleviate or eliminate the safety hidden trouble of the tailings pond,especially to ensure the dynamic stability of the tailings pond under the earthquake has been paid much attention by mining enterprises and government departments.Tailings are the slag of ore treated by the concentrator,which belongs to artificial sand and is piled up in the tailings pond.Tailing differs from the natural sand.The function and construction method of the tailings pond make it different from the water dams and earth-rock dams.Tailings is the construction material of tailings accumulation dam.Its mechanical properties determine the stability of tailings dam.The seepage line divides the tailings dam body into saturated zone and unsaturated zone.The mechanical properties of saturated and unsaturated tailings are different.For this reason,tailings sand and tailings silt were selected as research objects in this paper,and GDS dynamic triaxial test equipment was used to study the dynamic characteristics in saturated and unsaturated states.The laboratory test results were compared with the on-site standard penetration test results for liquefaction.On this basis,the numerical simulation of the dynamic stability of the tailings pond in the area of 8° seismic fortification intensity is carried out by using the time-history analysis method,and the dynamic stability of the tailings pond in the area of high intensity is discussed.The main work and achievements are as follows:(1)The dynamic characteristics of tailings sand and tailings silt under saturated and unsaturated conditions are studied.Dynamic parameters such as dynamic strength,dynamic shear modulus and damping ratio of tailings under different density,confining pressure and saturation were obtained by dynamic triaxial test.The dynamic characteristic parameters of tailings and natural sand were compared and the differences were found.The results show that with the decrease of saturation,the dynamic strength of tailings will gradually increase,and the failure form changes from liquefaction failure to large deformation failure.Seed-idriss model and hardin-drnevich model were established to characterize the dynamic characteristics of unsaturated tailings with saturation parameters.(2)The dynamic characteristics of tailings under different reconsolidation degree were studied.The effects of confining pressure and dynamic stress on liquefaction characteristics of tailings sand and tailings silt with different degree of reconsolidation were studied by dynamic triaxial test.The results show that the liquefaction resistance of the tailings will be improved after the reconsolidation.The stability of the tailings dam will be improved after a period of time reconsolidation.The quantitative relationship between the degree of reconsolidation and the liquefaction resistance of the two tailings in the reconsolidation process is established.The effects of confining pressure,dynamic stress and particle size on the dynamic performance of the reconsolidation tailings are analyzed.(3)The shear wave velocity characteristics and influencing factors of saturated and unsaturated tailings are systematically studied.The shear wave velocities of tailings with four different particle sizes were measured by GDS dynamic triaxial test system with bending element.The results show that the shear wave velocity of tailings increases greatly with the decrease of the pore ratio under different saturation conditions.The relationship between effective stress and shear wave velocity is a power function.With the increase of effective stress,the shear wave velocity of tailings increases gradually.(4)The shear wave velocity formula of tailings is compared with field test data.The reliability of shear wave velocity formula for tailings is verified.A prediction formula for shear wave velocity with particle size characteristic parameters is presented.(5)The applicability of sand liquefaction discrimination method in tailings in China and the United States is analyzed.In China,standard penetration test method is recommended,and seed-idriss method is adopted in the United States.Two methods were used to distinguish and compare the liquefaction area of three tailings ponds in China.The results show that the seed-idriss method obtained a larger liquefaction discrimination region and the liquefaction discrimination result was conservative.However,considering the complexity of tailings dam structure,seed-idriss method is recommended as a supplement for the liquefaction discrimination of the deep area of the high-pile tailings pond,and the result is safer.(6)Numerical simulation is carried out for the dynamic stability of tailings ponds with different dry beach surface lengths in high intensity areas.Taking the Xiaodae tailings pond as an engineering case,the saturated and unsaturated zones in the dam body are considered,and the influences of different dry beach lengths on the liquefaction area,safety coefficient and permanent deformation in the tailings pond are analyzed by time-history analysis.The results show that with the increase of the dry beach length,the area of the liquefaction area in the tailings pond will decrease,the safety coefficient will increase,and the permanent deformation will decrease. |
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