Research On The Dynamic Stability Of High Tailings Dam Under Earthquake Action

The tailings pond,which is formed by intercepting tailings and tail water through the embankment of tailings dams,not only occupy a large amount of land,but also is a source of artificial debris flow with high potential energy.Once the tailings dam is broken,it will not only overwhelm and impact the living and production facilities downstream,but also may cause serious environmental pollution.The statistics on the accidents of tailings dams show that the earthquake is the second most common cause of the tailings dam crash.China is a country rich in mineral resources,and also an earthquake-prone country.There are many mineral resources hidden in the areas around seismic zones.The tailings pond is the necessary facilities for the exploitation of metallic and nonmetallic mineral resources,and tailings pond must be constructed at the same time of the mining of mineral resources.Due to various reasons,tailings dams are constructed by the upstream method in most China's tailings ponds,which has relatively poor seismic performance.And the heightening of tailings dam and diminishing of tailings particles make the safety production situation of tailings ponds in seismic zones more severeThe structure of tailings dam has obvious anisotropy,heterogeneity and temporal and spatial variability,and earthquakes are random,sudden and destructive,therefore,the seismic problem of tailings ponds is very complicated.The present thesis focuses on the study of two cases,the operating Xiaodae tailing pond of Liangshan Mining Company and the proposed Yangtianqing tailing pond of Yunnan Gold Group,with the objective of gaining knowledge of the dynamic characteristics of tailings,analysis method of dynamic stability of tailings dams,seismic response characteristics of tailings dams and seismic measures and its reinforcement effect,in order to improve the understanding of the seismic response characteristics and damage mechanism of the tailings dam,based on the comprehensive research methods of theoretical analysis,laboratory test,numerical simulation and engineering example.The research results not only provide guidance for the design and construction of the actual projects,but also,provide technical support for improving the safety situation of the tailings ponds in seismic zones.The main results are as follows:(1)The dynamic characteristics of the dam material,tailing silty sand and tailing silt,which are the most common and sensitive to the seismic action in the tailings dam,were tested by dynamic triaxial test with two different density conditions.And the dynamic characteristics of tailing silty sand and tailing silt and the influence of density on them were obtained.(2)The dynamic characteristics of tailing silty sand and tailing silt in secondary liquefaction and the effect of pore pressure dissipation on their dynamic characteristics after the first liquefaction were studied by using GDS dynamic triaxial test system.The change laws of dynamic pore pressure,dynamic deformation and dynamic strength of tailing silty sand and tailing silt in secondary liquefaction and the influence of dissipation of excess pore pressure on these laws were obtained,which provides a theoretical basis for further understanding the impact of aftershocks post-earthquake on the stability of tailings dams in the earthquake-prone areas.(3)Considering the destruction of the tailings dam caused by earthquake can be divided into two aspects of liquefaction flow damage and non-liquefaction deformation damage,the procedure and methods of dynamic stability analysis of tailings dam with the comprehensive consideration of liquefaction range,safety factor time-history change and permanent deformation distribution were proposed based on existing research results,and the values of seismic magnitude,seismic wave duration,equivalent cycle number and shear stress ratio correction coefficient corresponding to different seismic fortification intensities were summarized and sorted,which provides a complete scheme for the calculation of the dynamic stability of tailings dams.(4)The seismic response characteristics and stability of the upstream high tailings dam were analyzed systematically.The results show that there are differences in the dynamic response characteristics of tailings dams and general earth-rock dam in terms of acceleration response and permanent deformation: 1)the peak acceleration of the initial dam(earth-rock dam)increases with the increase of the dam height,but the relationship between the peak acceleration and the height of the tailings embankment is not significant;2)the permanent deformation in the horizontal direction of the tailings embankment is greater than that in the vertical direction,and the permanent deformation is not monotonous with the dam height.By analyzing the influence of the length of dry beach,height of tailings dam,seismic acceleration and vertical seismic action on the safety factor and permanent deformation of tailings dams,it is found that the minimum safety factor of the tailings dam in the earthquake is linearly related to the influencing factors,and the seismic subsidence at the crest has a nonlinear relationship with the influencing factors.(5)The time-history change laws of safety factors of tailings dams were analyzed,and the calculation methods of the minimum average safety factor and the average small safety factor for the quantitative characterization of the degree of seismic safety were improved based on the characteristics of the fluctuation and reduction of the transient safety factors in the earthquake,which can effectively improve the reliability of tailings dam risk assessment under earthquake action..(6)To verify the poor seismic performance of the upstream tailings dam quantitatively,the calculation models of the three types of high tailings dams of upstream,downstream and centerline with the same safety margin pre-earthquake were constructed.The influences of earthquake action on the dynamic stability of the three types of high tailings dams were analyzed and compared.The effects of different seismic measures(slowing down slope ratio,heightening of initial dam,increase of dry beach surface length and additional level drainage)of upstream tailings dam were analyzed,which provides the basis for selecting better seismic measures for seismic design of tailings dam.(7)Taking the proposed Hetaojing tailings pond as the project case,the static and dynamic stability of the upstream high tailings dam in the high-intensity seismic area was systematically analyzed and judged,and the engineering measures to improve its stability were put forward,which provides a reference for the construction of the tailings pond in the earthquake area.