| A tailings dam is not only a very complex geotechnical structure, but also one of the largest resources of mining hazards. According to the geographical distribution of tailings dam, of which most are located in permafrost areas. In addition to the existence of conventional risk, the tailings reservoir of permafrost zone also faces the danger brought by freezing and thawing cycles. So far, domestic and foreign research results on tailings mechanical properties under conditions of freeze-thaw cycles are relatively rare, so it is the necessary to conduct research on tailings mechanical properties under freeze-thaw cycles, which not only provides basic data for tailings dam stability analysis, and can enrich the basic theoretical knowledge of mechanical properties of tailings in permafrost regions. In this paper, the test material is Copper mine tailings from Maanping mine waste comprehensive utilization co. Ltd.. By the method of artificial freezing, through a lot laboratory experiments, study and analysis of the physical and mechanical properties and its influencing factors of direct freezing tailings and tailings under freeze-thaw cycle conditions. Taking the Xiaodae tailing pond of Maanping mine waste comprehensive utilization co. Ltd. for example, the tailings dam stability under normal conditions and under conditions of freeze-thaw cycles were calculated and analyzed. Results are as follows:① For the geographical distribution data of Tailings pond in China, combined with regional division of frigid climate in our country, the specific distribution of tailings in permafrost region in China was analyzed, and tailings pond hazards in permafrost regions were summarized.②A laboratory study through the uniaxial compression tests has carried out on mechanical properties of frozen tailings, including four types tailings(medium sand, fine sand, powder sand and silt) and four factors(average particle size, density, moisture and loading rate). The results show that the frozen tailings samples under uniaxial compression have three types of failures, namely, incline plane shear failure, lateral tensile failure and mixed failure. The whole stress-strain curves of frozen tailings samples can be divided into four stages, namely, the initial stage of strain softening, linear strain stage, nonlinear strain hardening stage, and nonlinear strain softening stage. In the four factors, the uniaxial compressive strength is related logarithmically with average particle size, exponentially with the dry density, linearly with moisture, and parabolically with loading rate, while the deformation modulus of frozen tailings is related logarithmically with average particle size, exponentially with dry density and loading rate, parabolically with water content.③Through permeability test and the triaxial shear test(UU test), the permeability, consolidation compressibility and shear strength of tailings were studied under the condition of freeze-thaw cycles. The results show that the permeability coefficient of tailings increases with the increase of freeze-thaw cycles and turns stable. The increment of tailings permeability coefficient is the largest after the first freeze-thaw cycle. Tailing compression coefficient a under 100 ~ 200 Kpa increases with the increase of freeze-thaw cycles with increasing speed. While the compression modulus Es reverses.During studying variation of shear strength with deformation modulus under the condition of the freeze-thaw cycle, tailings particle size, density and moisture content impacting the mechanical properties of tailings were taken into consideration.The results of the study showed that, with the increase of the freeze-thaw cycles, the cohesive and deformation modulus decreased then turned stable, the friction angle increased then turned stable. The freeze-thaw cycles have weaker influence on tailings particle size. At the same freeze-thaw conditions, the cohesive and deformation modulus increase with the increase of density. The friction angle increased then turned stable with the increase of density. For the same dry density of the tailings, its cohesive force and deformation modulus would be reduced after freeze-thaw cycles. At the same freeze-thaw conditions, the cohesive and deformation modulus decreased with the increase of moisture content. Different moisture contents had different influence on various parameters. Freeze-thaw cycle had a greater influence on the cohesive force of tailings samples with the moisture content of 5%- 10% and a greater influence on the deformation modulus of tailings samples with the moisture content of 15% and a greater influence on the friction angle of tailings samples with the moisture content of 10%.④ For example of the Xiaodae tailing pond of Maanping mine waste comprehensive utilization co. Ltd., by the limit equilibrium method, tailings dam stability under normal conditions and under conditions of freeze-thaw cycles were calculated and analyzed. The results show that after freeze-thaw cycles, the safety factor of the three conditions compared with the conventional conditions are reduced. The stability under the three conditions(normal condition、flood condition and special condition) of the Xiaodae tailings dam were calculated, after the freeze-thaw cycles. The safety factors of three kinds of conditions reduced.So, the tailings dam located in cold areas should have more attention regarding the stability. The stability of the tailing dam could be affected by conventional factors and freeze-thaw cycles due to seasonal change, which reduces its stability. |
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