Cable Bolting in Underground Mines

What is a Cable Bolt?

A cable bolt is a flexible tendon made of multiple steel wires twisted into a strand, which is then grouted into a borehole. These bolts are typically installed at regular intervals to reinforce and stabilize the walls, roof, and floor of underground or surface openings in mines. Cable bolting is a highly versatile support method because the flexible strands can bend around tight curves, allowing for installation in confined spaces. Additionally, they can be customized with different wire configurations to suit various performance needs. Multiple strands can be placed in a single borehole to increase tensile strength, provided the hole is wide enough. Cable bolts can also be combined with other support systems like shotcrete, mechanical bolts, or grouted rebar for enhanced stability.

How Cable Bolting Works

The strength of a cable bolt is transferred to the surrounding rock mass through grout, typically made of Portland cement and water. Some mines add special additives to improve the grout's pumping properties. While resin and shotcrete have been explored as alternatives, cement grout remains the most common. Innovations like fiberglass cables are also being developed as potential replacements for steel strands. This guide focuses on traditional seven-wire steel strands and cement grouts.

Importance of Cable Bolting in Mining

Safety is a top priority in mining and construction. In smaller tunnels, methods like mechanical rock bolts, shotcrete, or grouted rebar are used to protect workers from falling rocks. However, in larger spaces such as major intersections, underground chambers, or active mining stopes, cable bolts are preferred due to their higher load capacity and ability to span greater distances. Larger spaces pose a higher risk of significant rock falls, making robust support systems like cable bolts essential.

Cable bolts can extend deep into the rock mass, reinforcing large volumes of rock and preventing separation along weak planes like joints. By maintaining the rock mass's continuity, cable bolts help mobilize its inherent strength, improving overall stability. They also prevent loosening and weakening of the surrounding rock by supporting surface blocks. This reduces the risk of progressive instability and failure, which can be both dangerous and costly.

Remote Installation and Pre-Reinforcement

Cable bolts can be installed remotely in long boreholes, reaching planned stope boundaries to pre-reinforce otherwise inaccessible areas. This is particularly useful in modern bulk mining methods. Cable bolts are often the only viable option for stabilizing inaccessible rock faces and controlling dilution.

Economic Impact of Dilution Control

Dilution control is critical in mining economics. Unplanned dilution—waste rock mixing with ore—can significantly increase costs. Waste rock must be extracted, transported, crushed, and processed, all of which are expensive. Additionally, it reduces the mill's effective capacity and can cause unscheduled delays. Cable bolts help minimize unplanned dilution by stabilizing the rock mass, preventing sloughing, and enabling safer extraction of larger stopes. This can lead to increased productivity and reduced costs.

Theoretical Dilution Values

Figure 1.2.3 illustrates theoretical dilution values based on span and sloughing depth for an unsupported stope. This highlights the importance of cable bolting in reducing dilution and improving mining efficiency.

Reference Source:

• Bawden, W. F. (1993). Rock Reinforcement in Mining.
• Elbrond, J. (1994). Economic Effects of Rock Dilution in Mining.
• Pakalnis, R., et al. (1995). Design of Underground Mine Support Systems.
• Stillborg, B. (1986). Professional Users Handbook for Rock Bolting.

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