Abstract

PYTLIK, A.; O'CONNOR, D.  and  CORBETT, D.J.. Resistance of yielding rockbolts to multiple impact loads. J. S. Afr. Inst. Min. Metall. [online]. 2023, vol.123, n.11, pp.539-555. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/776/2023.

The resistance of yielding rockbolts to multiple impact loads was tested by means of a drop hammer. The methodology was based on the ASTM D7401-08 standard as well as the requirements specified for rockbolts by Luossavaara-Kiirunavaara Aktiebolag (LKAB - a Swedish mining company) and the Safety In Mines Research Advisory Committee of South Africa (project number GAP 423). During the tests, the loading force and bolt elongation were measured with a sampling frequency of f_s = 19.2 kHz. In order to analyse the phenomena involved, the tests were recorded using two independent high-speed video cameras (600 and 1000 frames per second) and one thermal camera (128 frames per second). The tests demonstrated that all the samples transferred double the gravitational potential energy of Ep = 50.85 kJ from the impact load of mass m = 2825 kg and impact velocity of v = 6.0 m/s without failure. Damage to the bolt-resin contact in the upper anchoring zone of the bolt in the steel tube occurred after subsequent impacts. As a result, the macro-deformed bolt exhibits additional yield, and its operation following the shearing of the resin bond is similar to that of a 'cone bolt'. Only one test resulted in damage to the threaded bolt rod-nut coupling, during the fourth impact; however, no damage to the bolt-resin contact zone was observed.

Keywords : yielding rockbolts; dynamic impact drop test; multiple impact loads; consecutive impacts; thermovision analysis.

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