| Tailings impoundment, where the tailing is filled, is always constructed byintercepting the valley or encasing the land. Tailings impoundment is one of the threekey projects which need be controlled well and the important origin of hazard in theresource in metal mine and non-ferrous metal mine. The operation of tailings pond hasa great effect on both the economic profit of the milling plant and the environment ofthe area closed to the pond and the life of the people nearby. According to the "National long-term science and technology development planning framework(2006-2020)", and the "key projects in the national science&technology pillarprogram" released by National Ministry of Science and Technology during the11th fiveyear plan, the failures of tailings dam has become an important study content in theprimary area. In addition, the management of the underground mines, open pit mines,and tailing pond was also suggested in the "national safely production in the12th fiveplan".There are some tailings ponds in the most provinces except Shanghai in China now.According to the statistics, there are about more than120000tailings ponds at the endof2008, and about200new dams are built every year. With the development of themining and beneficiation industry, some new problems appear in the operation oftailings pond. For example, the heights of the old dams increase as a result of expandingthe pond volume, because of the shortage of land and the environment protection. Therecord of the height of the dam was renewing continuously. The highest dam is about260.0m and the number of the dam with the height more than200.0m is more than100.The increase of the mines yields result in the increase of tailings. The raising rate of thedam increases with the years. One level sub-dam is piled every year with the increase of2.0-3.0m in height in the past, but nowadays, four to six levels sub-dam is piled withthe increase of8.0-12.0m now, the height of some dam even increases by20m a year.Under the condition of high raising rate of the height, the existing method for tailingsdam construction is not suitable, and resulting some hazards to the tailings pond. Somenew dams turn to a danger just after a short time usage, has a very bad influence on thenormal operation. Therefore, the new construction method is necessary to satisfy therecent demands for the purposes of saving land and environment protection.The Xiaodae tailings pond is the object in the present study, on-site observation, laboratory test, theoretical analysis, and numerical modeling were adopted to study thekey mechanics problem and the construction method. The purpose of this study is tosolve the urgent problem in the mines and to serve for the safe production.The main content and the innovation in this paper are as follow.①The basic process of utilization of mineral resources and the origin of tailingsare introduced. The classification of the tailings material and its physical andmechanical properties are reviewed. The basic types of piling of tailings on ground, andpiling method and its feature were summarized. It is predicted that the highconcentrations of tailings (cone method) is a major development of the tailings pilingon the ground. The types and the reasons for the disasters occurring to the tailing pondsat home and abroad are analyzed. According to the statistical data, the main reasons ofdisaster for tailings pond in China can be roughly divided into two categories:(1) theability for surviving in the flood is poor and cannot satisfy the requirement of thedisaster control, especially for the extreme weather;(2) the stability of tailings dam ispoor, the slope surface, and the leakage of foundation or abutment occur easily, causingthe dam break.②The formation process of the upstream tailings dam and its property are thebasement for the structure analysis. The on-site testing indicates that the regularity oftailings deposition along the dry beach and the consolidation of the tailings materialunder gravity field. The results show that the density of the two main types of tailings(sand and silt) becomes greater with the depth increase. The sensitivity of the tailingssand is even greater. The laboratory test shows that saturation density and dry density ofthe tailings also gradually increased, with little change after144~168hours. Thetailings sand with better engineering and mechanical properties is more suitable as thematerial for dam construction.③According to the status of tailings ponds in China, the property of the tailingsponds can be summarized as wide distribution, small scale, high proportion of thetailings pond with risk. The safety situation is very serious. The quantity and quality oftailings pond are discussed, the results indicate that the two main tendencies:(1) themass of tailings increased by multiply times;(2) tailings particles become even finer.④Some new concepts and definitions were suggested to the fast high tailingsdam. The two parameters for classification from the existing tailings pond (capacity Vand the dam H) are introduced, and the dam height is regarded as a more importantvariable. Based on the literatures reviewed,100.0m is regarded as a suitable reference height for the high dam. It means that the minimum height of the high dam is100.0m.The raising rate of the tailings dam is defined combining with the formation of thedams. Another conception, storage capacity of unit dam height was also suggested. Thehigh raising rate is unfavorable for the stability of the tailings dam. The high storagecapacity of unit dam height is better for choosing the dam.The reason of the formation and the disadvantages for the high dam in China wereanalyzed, it will be a reference for the tailings dam design and operation.⑤The engineering mechanics of the dam was modeled, and the maximum heightof the dam and the limit raising rate were got. The stability of the high dam for differentkind tailings materials were carried out. The prediction correlation was got for the limitheight of the tailings dam, the prediction agrees with the practice. With the correlationgot, the regularity of the raising rate and the limit height of the dam were calculated forthe four kinds of tailings. With the increase in the raising rate of the dam, stability of thetailings dam is decreased. If the factor of stability in the calculation model is fitted at1.0, the raising rate limit per year is24.0m,18.0m,12.0m, and6.0m for the coarse sand,the fine sand, the silt, and the fine clay respectively. If the stability factor in thecalculation model is fitted at1.05, the limit values are24.0m,18.0m,12.0m, and6.0mfor above four kinds of tailings.⑥The building of the tailings dam was analyzed, and concluded that the key factorto control the rising rate of dam are the deposition of the sub-dam and the formation ofbeach. Based on the existing method for building the fast constructing sub-dam, twonew methods, swirl hierarchical segmented distributor and template method of damconstruction. These methods can not only solve building the sub-dam effectively, andalso reducing labor intensity because of the machines used. In addition, the regionalmanagement of the beach was suggested; it can effectively improve the strength of thedeposition of beach. Using these methods and technology mentioned can solve theproblem of rapid rising of the tailings dam.⑦As an example, the new project of Xiaodae tailings pond was analyzed. Thereare two main characteristics of this project. These are fast rising rate and high damheight, the average annual rising rate is18.0m and the design height is185m. It is atypical high dam. The cyclone classification building method was selected according tothese characteristics and the surrounding environment. The seepage field, the stability,and the stress and strain of the dam are calculated with the method of numericalsimulation. The results show that the requirement of building the high dam can be meet with the new methods. For the safety and stability of the tailings dam, it demands thatthe dam level drainage system must be set, lowing down the phreatic surface of the damto ensure the stability.Through the cyclone classification method has been developed in the project oftailings dam, it is to solve the problem of lack of coarse tailings. Combing with theupstream method to solve the high increase rate of dam is a new trying at home andabroad. The application in Xiaodae tailings dam is the first trial. It should be regard assuccessful project according to the operation condition up to now.These results not only solve the problem in the real production in Xiaodae tailingspond and have a greater economic and social effect, and also have high academic valuein designing the mine tailings pond. It will be a good reference in the tailings damconstruction. |
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