Australian Mining Consultants Pty Ltd. (Perth, Australia):

Louchnikov V. N., Principal Mining Geotechnical Engineer, e-mail: vlouchnikov@amcconsultants.com
Sandy M. P., Director

Institute of Problems of Comprehensive Exploitation of Mineral Resources (Moscow, Russia):
Eremenko V. A., Principal Researcher, Doctor of Engineering Sciences

Geobrugg Company (Perth, Australia):
Bucher R., General Manager

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.

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