National University of Science and Technology MISiS, Moscow, Russia:

A. S. Voznesenskiy, Professor, Doctor of Engineering Sciences
V. V. Koryakin, Assistant, koryakin@inbox.ru

GAZPROM Geotechnology, Moscow, Russia:
E. A. Voznesenskiy, Deputy Head of Department, Candidate of Engineering Sciences

In mining as well in underground and mine construction, personnel face danger from uncontrollable roof rock caving, which is prevented by strata bolting. One of the basic methods for strata bolting control is measurement of bolt pull-out force. Limitations of this method include failure of load measurement in loose roof due to formation of rust at bolt heads, which brings the risk of bolt tearing-off and impact blow hazardous for test engineers. This article discusses the shock response spectrum method based on analysis of bolt response to the action of shock. The informative parameters are the amplitude A and frequency F of maximum response spectrum. The authors describe a preproduction model of a control device tested in stopes at Novomoskovsk gypsum deposit, where support uses steel–polymer rock bolts 1.2 and 2 m long. The examples are given of spectra of bolt response signals and of the diagram of rock bolt state shown as a point in the plane of the informative parameters F–A. The finite element modeling has demonstrated connection between the informative parameters, state of support and properties of roof rocks, which may be considerably complex and make it difficult to interpret results in practice. The alteration of roof rock properties with time leads to an increase in acoustical attenuation of roof rock vibrations and to a decrease in elasticity modulus of roof rocks. The former factor contributes to a decrease in amplitude of maximum response spectrum, while the latter factor sustains a rise in this amplitude, which conditions ambiguousness of data interpretation. It is suggested to eliminate ambiguousness using an additional parameter—acoustic Q-factor. Under development is a control device version based on the microprocessor technology that enables complex multiparametric algorithms of signal processing and interpreted data visualization, which will enable determination of roof rock condition on the spot in a mine.
The study was accomplished according to research plan No. 109 in the framework of the basic part of state task No. 2015/113 in the area of scientific work for 2015.
The authors express their gratitude to V.B. Ivanov for the help in the practical realization of the preproduction model of the control device for roof rock bolting in underground mines.

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