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Louchnikov V.N.,Australian Mining Consultants Pty Ltd. | Eremenko V.A.,Institute of Problems of Comprehensive Exploitation of Mineral Resources | Sandy M.P.,Australian Mining Consultants Pty Ltd. | Bucher R.,Geobrugg Company
Gornyi Zhurnal | Year: 2014

Special requirements are imposed on the support of underground excavations driven in highly deformable and rockburst-hazardous rock masses, particularly, the requirement of high energy absorption. This requirement applies equally to rockburst prone rocks as well as squeezing ground. Surface support is considered a weak link in the chain of the underground excavation support for dynamic conditions. Selection of a support type to meet the dynamic loading requirements is based on four key parameters: distribution of load between rock bolts and surface support; peak load at failure of each element of support; maximum displacement at failure; and energy absorbed by each support element at failure. The tests produced the relationship between the experimental data and stiffness of the model "rock mass." It was found that 25% of energy going into the support system is absorbed by mesh and 75% by rock bolts in the case of "stiff rock mass." For the "soft rock mass" case, the distribution is 70/30%, respectively. The test results obtained on various support types in Western Australia are presented in Fig. 9 and Table 1 [7-9]. The tests at the same boundary conditions showed that high tensile chain link mesh Geoburg S95/4 absorbed energy of to 18 kJ/m2 and welded mesh - 2.6 kJ/m2. It was found that energy absorption in "soft" boundary conditions is approximately twice as much the energy absorption in "stiff" boundary conditions. It was found that energy absorption by fibre-reinforced shotcrete (FRS) grows by 10% per each added kilogram of synthetic fibre in the shotcrete mixture, and the increase in the FRS layer thickness by 25 mm doubles its energy absorption capacity. When designing a ground support system, the safety versus costs balance should be well understood. In relation to ground support for dynamic conditions, the costs of each element of the support are normalized to the unit of energy absorbed by this element. The total cost of a ground support system is a combination of product price, machinery depreciation and labor costs that are known in a mine. Support cycle times were obtained from time-and-motion studies.* The study was conducted within the fundamental research program ONZ-3 of the Russian Academy of Sciences.

Sandy M.P.,Australian Mining Consultants Pty Ltd. | Lushnikov V.N.,Australian Mining Consultants Pty Ltd. | Eremenko V.A.,Russian Academy of Sciences | Bucher R.,Geobrugg Company
Gornyi Zhurnal | Year: 2013

Important characteristic of support in severe-strain medium is its functional capacity for spring and compliance, saving the holding capacity at the same time. Understanding of support deformation mechanisms with improvement in the process of interaction of rock mass and support elements is the necessary part of designing of reinforcing systems, which make it possible to increase the efficiency and provide the safety of mining operations. There are shown the basic support deformation mechanisms, observed on the mines, developed in massifs of layer rocks with high inclination to deformation. Monitoring of shear strains helps to understand the mechanism of influence on functional capacities of anchors. Obtained data were used for laboratory testings and during the projecting of shear-resistant supports. Experience of extraction maintenance on Australian and Canadian mines at great depths is presented in this article together with technical and technological measures for the choice of support and strengthening systems for specific conditions. Mechanisms of control of deformations of enclosing excavation massif are considered from the point of designing and choice of supports. The possibilities of mine monitoring are also considered in this article.

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