SSAB’s newest expandable rock bolt — the
Virsbolt 240 light. (Photo: SSAB)

As demand grows and requirements become more stringent, bolt manufacturers, OEMs, industry and academia are coming together to advance the capabilities of bolts, rigs and monitoring systems.

Rual Abreu, rock reinforcement director at Normet, explained: “Mines are being developed to ever increasing depths to reach resources. These depths subject the rock mass to significant stresses and therefore squeezing/bulking ground and seismicity have become a challenge for many mines. Similarly, extracting ore from great depths is costly, creating a need to optimize ground support process efficiency and installation time for the mine to remain cost competitive.

“The most critical focus in the design of new ground support technologies and their installation is safety. These three drivers: deeper mines, operational efficiency and safety, have resulted in several key trends…”

According to Abreu, these are:
• Ground support technologies are being developed to offer a wider range of yielding and dynamic rock reinforcement options and designed to cope with and control squeezing and seismically active ground.
• Increased understanding of ground support applications has seen a transition from designing independent products to ground support systems in recent years. These comprise several complimentary products that collectively offer higher performing ground control solutions.
• To reduce operational costs, products are being designed to offer reduced installation cycle times. This minimizes time losses associated with installation.
• Mines are becoming less focused on the per-unit-cost of ground support products in favor of looking at the overall operational cost of support. This has allowed product unit prices to increase year on year with the proviso that the benefits of these products on the overall operational cost provide a net benefit to the mine.
• The greatest concern for most mines is the safety and longevity of the operation. This has seen greater focus placed on testing, qualifying and fully understanding products through laboratory and insitu field tests that closely represent loading scenarios ground support could be subjected to long-term. These include dynamic (high-speed) loading of bolts, shear loading, combination loading (tensile and shear simultaneously) and corrosion testing of products.
• A new trend that is emerging is sustainability focused. In the pursuit of greener technologies, many rock reinforcement suppliers are developing products with reduced CO2 and environmental impact. The use of green steels (sustainably produced steel) is also beginning to emerge.

“Ground support has become far more scientific in its application over the past 20 years,” Abreu told E&MJ. “In the past, the focus was more on unit price and operational speed, with less focus on safety, longevity and understanding how products would perform over time. Many mines are now faced with ground support challenges today because of inadequate ground support technology that was installed into the mine years ago.

“Geotechnical engineers are also far more knowledgeable on the design and application of ground support and are requesting to be more closely involved in product design and testing. The result of these factors is greater attention on product design, grades of material and quality control than before.”

Normet Expands SDDB’s Reach and Trials New Cable Bolt
Over the past 12 months, Normet has accelerated the rollout of its Self-Drilling Dynamic Rockbolt (SDDB). This product is designed to address all of the above constraints. The bolt controls squeezing and seismically active ground conditions by offering significant yielding of the bolt tendon.

“Conventional rock bolts typically snap when subjected to displacements exceeding a few millimeters, whereas the SDDB is able to tolerate rapid and large displacements in the rock mass without a loss in its tensile capacity,” said Abreu.

“The SDDB is further designed to offer accelerated installation times when paired with our RBG pumpable resins. The combination of these two products provides a high-performance system suited to either self-drilling single pass installation, or a more cost effective two-pass installation (non-self-drilling) process using mechanized bolting equipment.” He added that the SDDB has seen unprecedented market uptake due to its ability to offer both product performance and operational efficiency gains at a fair cost.

Normet is also expanding its cable bolting offering to include a range of spiral indented cable anchors. These are flexible long anchors with a specially prepared surface-finish that enhances the mechanical adhesion of the cable into the encapsulating resin or grout. This improved adhesion increases the stiffness of the installed support and can shorten the critical bond length required to anchor the cable.

In some applications, this can allow for a shorter cable to be used, saving time in drilling the support hole and reducing the cost of the cable. Abreu said the Spiral indent cable performs well when paired with the RBG pumpable resin system, allowing effective support to be achieved within minutes, whereas grout installations take several hours before it’s safe to work under the installed support.

“In Canada we have two new trials underway, the first is cable anchored with pumpable resin as described above, and we’ve seen great results in-terms of operational speed,” he said. “We also have a trial underway in Canada installing SDDBs using drilling rigs rather than bolting equipment. This allows mines to use their drill rigs as dual function equipment that can also install ground support. It requires modification of the drill drifter to be able to inject resin as well as drill.”

Normet will be showcasing its SDDB and cable anchor product systems at MINExpo INTERNATIONAL in September, and Abreu hinted that the company also has some new technologies focused on dynamic rock reinforcement that E&MJ readers can look forward to later this year.

SSAB’s Virsbolt Goes Light
SSAB has recently launched a new expandable rock bolt — the Virsbolt 240 light. This weighs 22% less than comparable bolts on the market.

Sara Valentin Eklöw is responsible for the SSAB Virsbo business. She explained: “The Virsbolt 240 light is made of higher strength steel which has allowed the thickness of the product to be reduced, but without compromising on performance. The benefits of the weight saving include reduced transport costs and, when installing the bolts in a mine, loading the carousel or manually installing the bolt, a 22% weight reduction will certainly be noticed by the operators resulting in better safety and an improved work environment.” She added: “What we see in the market is the increased need for dynamic bolts as mines go deeper and experience more seismic activity. Still, productivity needs to be high. Bolts also needs to be cost efficient and safety is always priority number one, so new bolts needs to live up to all of those challenges.”

“What we see in the market is the increased need for dynamic
bolts as mines go deeper and experience more seismic activity.”
(Photo: SSAB)

Looking ahead, SSAB is developing a 16-ton bolt in a smaller size — the Virsbolt 160 small — meaning that, with the same sized hole and bolt, mines can get more pull load than market standards, which are at 12 tons. “We’re also developing a stronger face plate, to handle pull loads over 12 tons,” said Eklöw.

Mining3 and UniSQ Develop Carbon Fiber Bolt
In July 2023, mining research organization, Mining3, and the University of Southern Queensland (UniSQ) announced they had partnered to develop a “revolutionary carbon fiber composite rock bolt” through support from the Australian Coal Industry’s Research Program (ACARP). This development aims to replace traditional steel and fiberglass rock bolts, offering improved performance and cost-effectiveness in mining and tunnel engineering.

Associate Professor Ali Mirzaghorbanali of the Centre for Future Materials at UniSQ is leading the research team in rock bolt mechanics and supporting Mining3 in the mechanical characterization of the new carbon fiber composite rock bolt.

“Steel rock bolts are heavy and prone to corrosion, while fiberglass composite rock bolts have limited capacity ratings and can be bulky in diameter,” said Mirzaghorbanali. “The introduction of lightweight and compact rock bolts is expected to significantly reduce drilling and installation costs in extreme mining and tunnelling environments.”

To expedite their market introduction, researchers from the Centre for Future Materials are using a state-of-the-art, industrial-scale, robotic double-ring braiding machine to enable automated manufacturing. The braiding machine is integrated with an industrial pultrusion line to demonstrate a fully automated, cost-effective rock bolt manufacturing process. UniSQ said this breakthrough has generated significant interest from the mining and tunnelling industries.

“We are thrilled to collaborate with UniSQ on this innovative project,” Mining3 CEO Jacqui Coombes said. “The development of carbon fiber composite rock bolts has the potential to revolutionize the mining industry by providing a lightweight, high-capacity, and corrosion-resistant solution. This partnership represents a significant step towards enhancing safety and productivity in underground operations.”

MRIWA Models for Better Bolt Design
Mining3 also worked with the Minerals Research Institute of Western Australian (MRIWA) between 2018 and 2023 on an A$1.27 million ($840,000) project to research in-situ rock bolt behavior underground to model and design improved ground support systems.

In the subsequent technical report, Mining3 explained that current rock bolt design is based mainly on the consideration of axial loading. However, underground in the mine, the rock bolts are subjected to complex loading conditions with axial, shear and combined loads (axial and shear).

“In most in-situ conditions, where a rock bolt crosses a discontinuity, the rock bolt will not fail by pure shear (guillotine) or pure axial tension, but by a combination of shear and tensile failure,” the team said. “This project aimed to establish the behavior of in-situ rock bolts by testing and monitoring with fiber optic sensors in the laboratory, and at underground sites to develop improved models and design improved rock bolt support systems.”

The project entailed extensive laboratory testing to understand bolt behavior under complex load conditions. To reduce the complexity of the mechanism of rock bolt loading, the bolts were tested without grouting. The tests were performed by subjecting the un-grouted rock bolts to a combination of axial and shear loads. The effect of these combined loading conditions on the rock bolt’s failure behavior was then analyzed.

Mining3 said: “Physical models were prepared to simulate the shearing in underground opening. The observations from the models were then used to analyze the effect of combined load on the safety factor of rock bolt reinforcement in underground openings using numerical modelling. The key finding of the analysis is the significant reduction in the actual safety factor of the reinforcement designed under combined load conditions.”

To establish the in-situ rock bolt behavior underground, and to validate and verify the numerical modelling of the rock bolt support system, a new and improved instrumented rock bolt was designed for underground testing. To analyze the data a new software tool was written, allowing the operator to observe the recorded strain values for a single fiber or for one rock bolt at a time through a graphical user interface. Further, the software provides the option to display the 3D shape and deformation of the bolt.

The instrumented rock bolts were first tested in a series of laboratory double shear tests. This research and testing showed that:
1. Current rock bolt support design methodologies consider only the axial capacity.
2. For typical rock bolt steel in Australia, the shear capacity is about 70% of the axial (tensile) capacity.
3. Most of the rock bolts are loaded along their length under varying combinations of axial, shear, and bending.
4. Under both shear and combined load with a gap condition, a low-stiff bar is suggested in the design since it can undergo more displacement.
5. Combined load conditions are still not considered in the rock bolt design; however, could decrease the rock bolt shear and axial capacity by 30% and 18%, respectively.

The results of the tests were used to calibrate numerical models to analyze the rock bolt behavior under combined loading when installed across a discontinuity. Based on the conclusions from analysis of double shear test models, a new method was proposed for modelling rock bolts under shear load in FLAC3D.

The instrumented rock bolts were tested during a two-month long trial at a hardrock gold mine near Kalgoorlie. The data collected demonstrated the capability of the instrumented bolt to provide a continuous monitoring of the rock bolt loading. The high density and continuous sensing of the complete length of the rock bolt led to the exact location and magnitude of the shearing. This data can be used to identify potential structures and help design and improve future ground support.

A new analytical model for the shear response of fully grouted rock bolts using the virtual work principle was proposed, and a method to consider the effect of plastic strain hardening of steel on post elastic shear behavior of rock bolt was presented.

“The analytical model has been validated with laboratory shear tests results. The validation of the analytical model with lab test results has shown that it can more accurately predict large shear deformation behavior of rock bolts,” stated the report. “Analytical models that do not consider the effect of strain hardening, overestimate the ultimate shear displacement by up to 35%. Therefore, it is important to consider plastic strain hardening in post-elastic shear behavior of rock bolt. The proposed analytical model outlines a method to do so.”

The project concluded that, under combined load conditions, 80% of the rock bolt axial load capacity should be assumed for the rock bolt design. However, in situations with large shear, this is further reduced to only 50%. For both conditions, if the displacement percentage is higher than 80% then the rock bolt selection should be reconsidered (i.e. low-stiffness bar).

Komatsu’s ZB21 bolter at the San Xavier mine in Arizona. (Photo: Komatsu)

Komatsu Launches Z2 Bolters
In May 2024, Komatsu introduced its second generation Z2 product line of small-class development drill and bolting equipment with various enhancements and additions, including the first battery- electric offerings within Komatsu’s underground hard-rock portfolio, an innovative pumpable resin system solution, optimized ergonomics and more.

The small-class ZJ21 jumbo drill and ZB21 bolter initially launched in 2020 with a common platform. The new Z2 bolters and jumbos also feature optimized operator ergonomics designed to maximize comfort and visibility, user-friendly intuitive controls and engineering for ground-level maintenance.

The second generation ZB21 is a small-class bolter featuring a fully enclosed ROPS/FOPS-certified operator cabin, intuitive operator controls, integrated patented screen handling and industry-leading drifters manufactured by Montabert. The bolter also introduces an optional Komatsu pumpable resin system using J-LOK P by Jennmar. The solution allows resin to be pumped into the drilled hole prior to bolt installation, permitting the use of more economical bolts and helping to decrease overall installed cost.

The second generation ZJ21 jumbo drill is a single-boom development drill with a fully enclosed ROPS/FOPS-certified operator cabin, innovative drilling feeds, advanced pilot hydraulics and renowned drifters manufactured by Montabert. Komatsu said that both product lines now include battery-electric versions featuring onboard, smart, opportunistic charging and are designed for seamless integration and compatibility with existing mine infrastructure. The ZB21 and ZJ21 are the smallest size-class drills and bolters to offer a BEV option and feature a modular battery driveline with 83 kWh of onboard energy designed for demanding tram cycles and the challenges of hard-rock mining.

“As underground mining operations increasingly shift toward electrification of their fleets, our innovative, battery-powered Z2 jumbo drills and bolters will support that pivotal transition. By integrating into existing infrastructure, we can help enhance productivity while helping to reduce operating costs,” said Johan Kempe, product director for underground drilling at Komatsu. “The rollout of our second generation Z2-class marks a milestone in our commitment to advancing mining technologies and building upon the proven success of our products to empower the future of mine operators.”

New Monitoring Systems from ThingWave
ThingWave, a startup created by researchers from the Luleå University of Technology and supported by EIT RawMaterials, unveiled a new 5G-enabled convergence sensor for underground mines in December 2023. This can effectively detect the convergence of tunnels and the tilt of walls and other load-bearing structures.

Any indicated deformations are reported to the client, providing real-time insights and ensuring proactive anomaly detection. The use of wireless communications enables fast and trouble-free installation of convergence sensors, and easy relocation where necessary. The produced data can be visualized in ThingWave Cloud, or in ThingWave RealMine3D.

The global rock bolt market was valued at $46.3 billion
in 2023. (Photo: SSAB)

The RBM-VX can measure bolt elongation up to 40-mm with 0.1-mm resolution as well as measure bolt rupture and vibrations. Lifetime is up to 10 years on a single battery, and the system supports 5G and LTE connections. Deformation data can be visualized in ThingWave’s tool for Digital Twins — RealMine3D — and the system is fully integrated into ThingWave’s Mining 4.0 digital platform.

“We have been successfully testing the RBM-VX in active mines to be able to assess the sensing performance, robustness, and connectivity,” the company said. “The data we have collected has resulted in new knowledge in how rock masses move due to ground pressure and blasting. We have been able to track wall movements in real- time using 5G connected devices.

“The RBM-VX represents a significant leap in ground support monitoring capabilities, doing away with the hassles of legacy sensor solutions based on cables with time-consuming installations as a result. The RBM-VX also enables other digitalization opportunities such as finegrain positioning, improved ventilation control and production efficiency. The use of ThingWave’s Mining 4.0 digital platform results in savings of tens of millions of dollars per year.”

Epiroc to Acquire Canadian Ground Support Business
On the business side of things, Epiroc has agreed to acquire the business of Yieldpoint Inc, a Canadian company that provides advanced ground support solutions for mining and civil engineering applications.

Yieldpoint is based in Kingston, Ontario, Canada. The company designs, manufactures and sells advanced digital geotechnical instruments and has customers worldwide. Its products include ground movement sensors and telemetry solutions which are primarily used for underground mining, tunnelling, and civil construction applications. Yieldpoint’s solutions help digitalize the ground support and create a safer working environment.

“Yieldpoint’s smart and robust monitoring solutions complement our ground support offering well, and expand our portfolio of digital solutions,” said Helena Hedblom, president and CEO, Epiroc. “Together we will offer high-tech ground support solutions that allow customers to operate in a safer environment and spend more time focusing on their operations.”

The acquisition was expected to be completed toward the end of the second quarter of 2024.