Your browser is not supported anymore.

We suggest changing from Internet Explorer to another option. The Internet Explorer browser is no longer supported by Microsoft. Please install or upgrade one of the browsers below.


Influence of Testing Configuration on the Performance of Paddled Energy-Absorbing Rockbolts under Impact Loading

Published: Rock Mechanics and Rock Engineering (2022)

 

Author(s): Greig Knox and John Hadjigeorgiou

 

Date: 26 June 2022

 

Overview: Deep and high-stress mines are susceptible to mining induced seismicity that can challenge the installed ground support. Under these seismic conditions, conventional rockbolts such as mechanical, fully grouted rebar and frictional rockbolts are often inadequate. This has led to the development of several yielding, high energy-absorbing rockbolts that can carry large loads as well as accommodate large deformations. In this category, paddled energy-absorbing rockbolts are more widely used at seismically active mine sites. The performance of energy-absorbing rockbolts is generally determined by the impact testing method, which consists of dropping a known mass from a given height to transfer the kinetic energy of the falling mass to the rockbolt that is installed in a steel tube. All impact tests employ one of two configurations: continuous tube and split tube. The continuous tube configuration simulates an impact load directly applied onto the rockbolt plate while the split tube represents a loading condition on a rockbolt when a rock block is ejected by an impact thrust. However, the influence of the split location along the testing tube on the behaviour of energy-absorbing rockbolts had not been addressed in the past. This paper presents the results of a comprehensive testing programme whereby it was demonstrated that the location of the split within the host tube controlled both the maximum plate displacement and dissipated energy recorded prior to the rupture of the rockbolt. This has a significant influence on the performance of paddled energy-absorbing rockbolts under impact loading conditions.

 

Download link: https://link.springer.com/article/10.1007/s00603-022-02945-1


Multi-modal loading of rock reinforcement under controlled conditions

Conference: Breaking new ground: A Modern approach of destress strategies in deep (mass) mining, Johannesburg, South Africa

 

Author(s): Greig Knox

 

Date: 7 April 2022

 

Overview: Rock reinforcement products are typically laboratory tested under singular loading conditions. This presentation explores the benefits and limitations of conventional testing methods for ground support; and introduces new testing methodologies intended to improve industry understanding of ground support behaviour in application.

 

Download link: https://sanire.co.za/documents/events/breaking-new-ground/860-ep-gs-multi-modal-loading-of-rock-reinforcement-under-controlled-conditions


Dynamic testing: determining the residual dynamic capacity of an axially strained tendon

Conference: Ground Support 2019, Sudbury, Canada

 

Author(s): Greig Knox and Adrian Berghorst

 

Date: 23 – 25 October 2019

 

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, resulting in the rupture of the tendon.

 

Download link: https://doi.org/10.36487/ACG_rep/1925_14_Knox


A practical design approach for an improved resin anchored tendon

Conference: Deep Mining 2019, Muldersdrift South Africa

 

Author(s): Brendan Crompton

 

Date: 24 – 25 June 2019

 

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.

 

Download link: https://doi.org/10.36487/ACG_rep/1952_13_Crompton


Introduction and application of the Dynamic Impact Tester

Conference: ARMA 2019, New York, USA

 

Author(s): Adrian Berghorst and Greig Knox

 

Date: 23 – 26 June 2019

 

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.

 

Download


The relationship between the magnitude of impact velocity per impulse and cumulative absorbed energy capacity of a rockbolt

Conference: ARMA 2019, New York, USA

 

Author(s): Adrian Berghorst and Greig Knox

 

Date: 23 – 26 June 2019

 

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.

 

Download


Qualification of Dynamic Ground Support

Conference: Caving 2018, Vancouver, Canada

 

Author(s): Adrian Berghorst

 

Date: 17 October 2018

 

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.

 

Download


An empirical comparison between new and existing laboratory-based dynamic sample configurations

Conference: Caving 2018, Vancouver, Canada

 

Author(s): Greig Know, Adrian Berghorst and Pieter de Bruin

 

Date: 17 October 2018

 

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.

 

Download Link: https://doi.org/10.36487/ACG_rep/1815_58_Knox


Relationship between energy per impulse and dynamic capacity of a rockbolt

Conference: Rock Mechanics – Experiments, Theories and Applications

 

Author(s): Koos Bosman (Open House Management Solutions), Martin Cawood and Adrian Berghorst

 

Date: 2018 

 

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.

 

Download


Increased agility for the research and development of dynamic roof support products

Conference: RocDyn-3, Trondheim, Norway

 

Author(s): Greig Knox and Adrian Berghorst

 

Date: 26 June 2018

 

Overview: 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..

 

Download