Mechanics Of High Tailings Backfill And Nonlinear Optimal Design In Deep Mining

Backfill mechanics is a new subject that is formulated with the development of the technology of filling mining. Coupling the Vertical Crater Retreat method with delayed backfill in high-level mining, the applying ranges of filling technology are extended, especially in deep, thick and large-scale deposit, and at the same time new research contents are tabled for backfill mechanics. Because there are not systematical researches on mechanical mechanism of high backfill and its correlative theories at present, the design of high level backfill is mainly carried out by experience method or analogical method which often leads the cements being wasted or the strength being lower than that of the requirement in engineering. In order to mine safely and effectively, it is necessary to establish the mechanical models of high backfill according to filling technology in deep mining, and to optimize design to reduce production cost. The main contents of this paper are included as follows.Via mechanical experiment to backfills with different cement-tailing ratios, their damage constitutive equations were established, and their mechanical characters and laws of energy releasing were analyzed. According to the damage constitutive models and the principle that the deformation energy of backfill under peak stress corresponds with releasing energy from excavated rock mass during deep mining, the reasonable match relationship between backfill and deep rock mass was explored, and the required strength of backfill in Dongguashan deep mine, Anhui province, was ascertained, as well as the feasibility of the minimal cement-tailing ratio being determined as 0.0833 in Anqing copper mine was investigated.For improving filling quality in deep mining, the gradation composition of classifying tailings was researched on fractal theory. Analyzing the data tested in a lot of mines, a neural network model which embodied the relations between strength of cemented tailings and content of cement, consistence, fractal dimension of porosity and correlating coefficient of fractal dimension was established, and the intrinsic laws between strength of classifying tailings and its gradation compositionwere researched. The research results show that the strength of cemented tailings increases with the decrease of fractal dimension of porosity, and the higher the correlating coefficient of fractal dimension is the higher the strength will be. According to the gradation composition model, with a method of chaotic optimization, the reasonable classification of mill tailings that owned optimum strengths was given, which has been applied in classifying design of mill tailings in Anqing copper mine. The applying results in Anqing copper mine show that not only the supply of tailings was increased, but also the strength of cemented backfill was enhanced, and filling cost was saved.According to the technologic characters of delayed high backfill, analyzing the mechanical actions between wall rock and backfill during deep mining, a mechanical model of layered filling body and the mechanical condition that backfill can be exposed at a random height were obtained. And with the method of fractal tree and renormalization group, a strength model of backfill in deep mining was established. Because of the complexity of deep mine and indeterminateness of backfill strength, according to the mechanical models proposed above, and using dependability theory and a method of game tree, a complicated problem to optimize the cement-tailings ratios for high backfill was solved successfully, of which the excellent effects were applying in optimizing the ratios of cement to tailings in No. 5 stope in Anqing copper mine.Being complicated deformation of backfill in deep mining condition, such as indeterminateness, randomicity etc., on basis of monitoring the deformations of high backfill in Anqing copper mine, their laws were analyzed with chaotic theory, and the results proved that the deformations of backfill hold the characters of chaos. Reconstructing phase space to time series of deformation of backfill with different cement-tailing ratios, their grey prediction models was established, and a reasonable period of high-level pillar stopping in deep mining was ascertained.