Study On Mechanism Of The Grouting Backfill In Caving Area With Strip Mining Under Buildings

Strip mining and backfill mining are main mining technology under buildings and important component of green mining technology. However, the former is restricted in colliery because of its lower extraction ratio, and the latter is little applied in coal mine by reason of its high cost and complex process. Based on the key strata theory, the grouting backfill in caving area with strip mining under buildings was proposed, which integrates the advantages of strip mining and backfill mining.The paper did further system research aimed at the basic theory of new technology.In order to evaluate the filling of the falling rock in caving area formed in strip mining, the surfaces characteristics and void distribution features of the falling rock were studied with fractal theory. The fractal models was constructed by the fractal geometry theory for the void distribution of falling rock in caving area formed in coal mining. The corresponding fractal dimensions of void distribution of caving area were determined according to mining geology condition and the parameters of coal working faces.Then, an effective calculating formula that controls filling volume was deduced from the fractal theory. The formula and the fractal models have been proven to be effective to predict voids-filling of caving area in Qidong coal mine, and they are applied in predicting the filling volume in caving area with strip mining under buildings.The conception of falling rock backfill with strip mining was defined in the paper. In order to study the mechanics character of falling rock backfill with strip mining, a set of experiment equipment was designed and manufactured, and the numerical simulation on the mechanics experimental scheme was executed with the PFC particle flow code. The factors influenced on the mechanics character of the backfill were analyzed by mechanics test in laboratory and numerical experiment,and the factors includes fill ration, fill means and rock property. The results show that falling rock backfill with strip mining is a favorable bearing structural body, which can reduce surface subsidence, and restrict lateral distortion of coal pillar if the backfill is subjected to confining pressure.By the physical simulation, the paper studied the characteristics of key strata movement when the grouting backfill in caving area is applied in coal mine, which can control the movement of overlying rock and the surface subsidence.After analyzing the difference of key strata fracture between grouting backfill and longwall mining system, the paper carried out further mechanism analysis. The experiment results and mechanical analysis show that the grouting backfill in caving area can extend the mining width when the key strata theory is used in designing strip mining. According to the engineering features of the grouting backfill in caving area with strip mining under buildings, the mechanics model of reducing subsidence by key strata-coal pillar-falling rock backfill was established successfully. Mechanism of reducing surface subsidence was analyzed when the grouting backfill in caving area with strip mining under buildings was applied.The mechanics mechanism of reducing subsidence by key strata-coal pillar-falling rock backfill was revealed after analyzing the results of the PFC numerical simulation and physical simulationThe paper put forward the principle of substitutional filling reducing subsidence equivalent. Design method of the grouting backfill in caving area with strip mining under buildings was established based on the theoretical research results. Furthermore the method was applied in the strip mining design of a county town and achieved favorable results. Based on green mining idea, an incorporate fill technology of coal mine and power plant was proposed, and preliminary design method has been used in mining industrial test scheme under buildings. In order to evaluate fill technology, the principle of the balance between mining out and backfill was proposed, and the balance between mining out and backfill was studied when the grouting backfill in caving area with strip mining under buildings was applied. The results show that the grouting backfill in caving area with strip mining under buildings can achieve the balance between mining out and backfill.