Combined Load Failure Criterion for Rock Bolts in Hard Rock Mines
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REVIEW
Combined Load Failure Criterion for Rock Bolts in Hard Rock Mines P. C. Pinazzi 1
&
A. J. S. (Sam) Spearing 1 & K. V. Jessu 1 & P. Singh 1 & R. Hawker 2
Received: 1 August 2019 / Accepted: 17 August 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Rock bolts are highly important underground to prevent falls of ground and thus, ensure safety. In situ, the ground reinforcement is subjected to a combination of loads, such as shear, tensile, and/or bending loads. Studies have been conducted to evaluate the effect of either shear, tensile, or bending loads on the ground support. However, only a few studies have been done to evaluate the effect of combined load on the rock bolt performance. In situ, the order of loads acting on the bar cannot be predicted, and more than one load can act on the bar at the same time. Thus, a hybrid failure criterion was developed that covered all combined loading conditions. Fifty-eight un-grouted laboratory rock bolt tests were conducted in total under two load conditions: applying shear displacement to the rock bolt and then tensile load to failure, and applying tensile displacement to the rock bolt and then shear load to failure. From the test results, the failure criterion was developed based on regression analysis. A nonlinear relationship was determined for the loading condition variations. The failure criterion presented in this paper can be used as a guide in the rock bolt capacity design under all loading conditions. Keywords Tensile load . Shear load . Bending load . Combined load . Failure criterion . Rock bolt design
1 Introduction Rock bolts are the primary ground reinforcement used to prevent fall of ground in situ. Every mine presents different conditions related mainly to geology, hydrology, and mining characteristics and conditions. These characteristics directly impact the loads generated along the rock bolt. In situ, the rock bolt can be subjected to a combination of loads such as shear, tension, and bending. These loads can be identified in the current ground reinforcement mechanism. It confirms that the rock bolts are subjected to a combination of loads, (Fig. 1) ([10], modified by [12]). Even though combined loads have been evaluated in previous research [1], no attempt has been done yet to consider its effect on the rock bolt capacity that should be used in the support design process.
* P. C. Pinazzi [email protected] 1
Department of Mining and Metallurgical Engineering, Western Australian School of Mines, Curtin University, 95 Egan St, Kalgoorlie, WA 6430, Australia
2
Minova Global, 102 Albatross Rd, Nowra, NSW 2541, Australia
Chesson et al. [2] and Fisher and Struik [5] developed failure criterion for structural bolts under combined load. Even though the failure criterion has been used to evaluate the effect of combined load on rock bolts, the results obtained in this study do not comply with the previously developed failure criterion. The load condition applied to the structural bolts was different from the one applied in t
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