Overview:
The specification of a tendon is stated as the capacity of the tendon in pristine condition on the day of delivery to the mine. A number of factors result in the degradation of the capacity of a tendon. Factors such as, but not limited to, installation quality, corrosion, and ground movement are all understood to reduce the residual capacity of a system. An understanding of the effects of the degradation of a tendon is important when determining the risk of an excavation. Rock support tendons are discretely tested quasi-statically (closure) or dynamically (seismicity) depending on the conditions expected with the mine environment. Although this testing is valuable, it is likely that a tendon subjected to rapid ground movement (seismicity) would first be subjected to some level of slow closure. This paper forms a basis for future work into determining the residual capacity of a tendon; the focus of this paper is to determine the residual dynamic capacity of an axially elongated tendon. Samples were axially elongated quasi-statically and fixed into place prior to being subjected to a single dynamic impulse (56 kJ), resulting in the rupture of the tendon, using the Dynamic Impact Tester from New Concept Mining. A trend of increasing ultimate dynamic load and total elongation (determined as the summation of the quasi-static and dynamic displacement) sustained prior to the rupturing of the tendon, was noted. However, the total energy absorbed by the tendon indicated the fact that the total energy of the tendon remained constant.

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Overview:
The use of resin-grouted tendons is a common ground support practice within the mining industry and various tendon designs are available. The support strength of a resin-grouted tendon is often constrained by the resin annulus between the tendon and the borehole. Effective mixing of the resin is typically achieved by ensuring the resin annulus does not exceed a specified maximum limit. Therefore, in some cases, the diameter of the tendon is dictated by the maximum allowable resin annulus and minimum diameter borehole that can be drilled and not by the support design requirements. The installation of tendons with mastic resin capsules is prone to gloving of the installed tendon by the capsule packaging, thereby debonding the tendon from the borehole, and compromising the mixing of the resin surrounding the tendon. This paper documents a practical investigation into the effectiveness of typical resin tendon designs in large annulus installations and the development of an improved tendon design for such cases.

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Overview:
New Concept Mining (NCM) has implemented the Dynamic Impact Tester (DIT) to conduct laboratory based dynamic testing on rock bolts. The DIT allows NCM to move rapidly through the R&D cycle for new rock bolts. This allows both a shorter time to market as well as comprehensive understanding of the performance of rock bolts. In addition to these benefits, the DIT is being used in several exciting ways to improve the understanding in the mining industry of the performance of dynamic ground support. An example is given where the dynamic testing database has been used to back analyze the quantitative performance of a Vulcan Bolt during an underground seismic event.

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Overview:
Laboratory-based dynamic testing provides an invaluable tool in the development of rock bolts for use in highly stressed, burst prone rock masses. While in most cases the laboratory-based test method is not a direct comparison to an in-situ installation due to the purely axial loading and variations in boundary conditions, it does provide an indication of the performance of the tendon system under dynamic loading. The aim of the research described in this paper is to provide an understanding of the effect of the impact velocity of the impact mass during a laboratory-based dynamic test. Understanding the effect of boundary conditions of laboratory testing will improve Geotechnical Engineers understanding of the performance in an in-situ installation. In addition, due to the limited number of dynamic test facilities, an understanding of the effects of the boundary conditions will aid in the comparison of test results for different products from different test facilities.

The research was conducted using an impact tester, whereby a known mass is raised to a known height defining the kinetic energy and velocity of the mass at the point of impact with the test sample after release. The impact velocity was varied between 2.7 m/s and 5.4 m/s, while the kinetic energy of the mass was maintained at 11.5 kJ. While a correlation between the impact velocity and strain rate of the system tested was established, due to the properties of the system tested, the range of impact velocity on which dynamic tests were conducted was insufficient to result in a considerable change in the average impact load, the cumulative proximal displacement and the cumulative maximum energy absorbed over multiple impulse. However, due to the reduction in the momentum of the impact mass the impact duration and displacement during each impulse in the series of impulses reduced.

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Overview:
A workshop presentation on current and future trends in qualifying dynamic ground support for underground mines. There are several facilities available to the mining industry when it comes to the qualification of ground support for dynamic environments in today’s underground environment. However are these sufficient, and what is the future of ground support qualification for this essential aspect of mining in the modern world.

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Overview:
Laboratory-based dynamic testing allows rockbolt developers to apply impulses of energy to a rockbolt in order to approximate some loading aspects that the rockbolt would experience during a rockburst in an underground mine. This data can be used to compare a rockbolt’s dynamic performance providing geotechnical engineers with useful information for designing their required ground support system. There are two general sample configurations commonly used in this type of dynamic testing – split-tube test and continuous-tube test. This paper summarises a proposed a third configuration – a multi-split-tube test.

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Overview:
Given the increasing need and benefit in better understanding and designing dynamic support elements, New Concept Mining built a new dynamic test machine, the Dynamic Impact Tester (DIT), at their research facility in Johannesburg, South Africa.

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Overview:
This presentation considers the differences in performance of ground support under quasi-static and dynamic loading and the various types of dynamic testing currently available to the mining industry. Specific focus is given to the methodology and results achieved from the dynamic laboratory testing of rockbolts as well as the presentation and interpretation of test results. A practical approach to better utilise laboratory results for the monitoring of support performance underground is also proposed.

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Overview:
The capacity of a rockbolt subjected to an impulse of energy varies as a function of the magnitude of the impulse of energy applied. This paper explores the relationship between the magnitude of the impulse of energy applied to a rockbolt and the resulting dynamic capacity. The result of this research shows that for a given velocity at impact, there is a linear relationship between the magnitude of the individual impulses of energy applied to a rockbolt and the resulting dynamic capacity of the rockbolt. The dynamic capacity of a rockbolt is not a constant value. During this research, the relationship between the magnitude of the impulse and the resulting displacement of the rockbolt is also examined.

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Overview:
New Concept Mining (NCM) has developed the Dynamic Impact Tester (DIT) capable of testing as many as 179 rock bolts in a period of six months, with no interruptions to mining operations. The limitations of the dynamic axial loading testing method are known, however, the DIT provides an efficient platform, on which a large number of tendon support systems can be compared under controlled conditions with increased agility. During the rapid development of new rock bolt products it is crucial to quantify the effects of high strain rates exerted by rock bursts on ground support systems. The DIT provides this capacity.

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Overview:
The introduction of a new testing configuration, whereby a split is introduced between each anchor pair along the entire rock bolt and the loading is applied to the washer. The purpose of the Multiple Split Tube test is to attempt to more accurately simulate the expected loading of the complete length of rock bolt in highly fractured ground. Since this new testing configuration loads the entire length of the bolt, an increase in the ultimate absorbed energy and deformation have been noted when compared to traditional split tube tests.

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