Laboratory studies of a high-strength roof bolting by means of self-extending mixtures

I. Sakhno¹, S. Sakhno¹, O. Isaienkov², D. Kurdiumow³

¹Donetsk National Technical University, Pokrovsk, Ukraine

²Industrial Institute of the Donetsk National Technical University, Pokrovsk, Ukraine

³Company of Mining and High-Altitude Work “AMC”, Wieliczka, Poland

Min. miner. depos. 2019, 13(2):17-26

https://doi.org/10.33271/mining13.02.017

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ABSTRACT

Purpose is to analyze parameters of a new method to fasten roof bolts with the help of nonadhesive mixtures extending while hardening along with the development of high expansion pressures.

Methods. The research, concerning forces applied while fastening roof bolts by means of self-extending mixtures, has been carried out under full-scale laboratory conditions using pressing-in method. Rock mass was simulated by means of concrete in plastic and metal forms, and steel pipes. The latter simulated ultimate rigidness conditions. Roof bolts were simulated by means of reinforcement steel fragments. In the context of the research, bolt diameters varied from 8 to 32 mm, and borehole diameters varied from 26 to 43 mm. Hydraulic 50-ton press was used for the tests. The testing results were applied to obtain regressive dependences of bolt fastening efforts in terms of different ratios between roof bolt diameter, borehole diameter, and incapsulation depth. Mine experiments concerning efforts to fasten Rockbolt System AG roof bolts of J64-27 type to strengthen chamber 1 of level 3 in Velychka mine were performed using a method of static bolt extraction. Hydraulic extraction device was equipped by ZEPWN CL 18T sensor and CL 162z-DW recorder.

Findings. It has been proved experimentally that operation mechanism of the roof bolts, fastened by means of self-extending mixtures during hydration hardening, is close to the modern energy absorbing bolts. Bolt diameter-borehole diameter ratio range, when ultimate effort of bolt fastening by means of extending mixtures is achieved, has been determined. Functional connection between the efforts to fasten roof bolts, using extending mixtures, and diameters of borehole and the roof bolt has been identified as well as linear connection between incapsulation depth and bearing capacity of the roof bolt.

Originality.A new concept to fasten roof bolts with the help of nonadhesive technique owing to their quazistatic compression between borehole walls, taking place as a result of hydration self-extension of mixtures which can achieve 30 – 50 MPa pressures under the conditions of zero deformations, has been developed. Regularities in the variation of efforts to fasten bolts, using the technique, depending upon roof bolt – fastening mixture – rock mass system geometry have been determined.

Practical implications. The results can be used to calculate parameters of roof bolting with high bearing capacity under the conditions of large deformations. The proposed fastening method may be implemented in mine workings.

Keywords: roof bolt, fastening of roof bolts, adhesion, rocks, stresses

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