Types of Tunnel Rock Bolts and Their Uses

Rock bolts are long steel rods or anchors, inserted into pre-drilled holes in tunnel ceilings or walls, used to reinforce rock mass and prevent collapse. Their primary function is to transfer unstable, loose, or fractured rock load deeper into the more stable rock mass, effectively “knitting” together the rock structure and ensuring overall tunnel safety.

1. Self-Drilling Rock Bolts

Overview

These are hollow steel bolts that can simultaneously drill into rock and anchor themselves in a single operation. The hollow core allows for cementitious grout to be injected after installation, further increasing the bond and enhancing reinforcement.

Uses

• Loose or fractured rock: Excellent in weak geology, where drilling holes for traditional anchors is risky.
• Wet conditions: The grouting process helps bind the bolt, even in percolating ground water.
• Rapid installation: Ideal for projects requiring fast support deployment.

Argentium supplies self drilling rock bolt systems designed for both mining and tunneling sectors, ensuring high productivity and safety margins.

2. Expansion Shell Hollow Rock Bolts

Overview

This type of tunnel rock bolt employs a mechanical shell that expands against the borehole when tension is applied. The expansion anchors the bolt firmly within the rock. Its design can also accommodate additional grouting if required.

Uses

• Immediate load bearing: Useful for circumstances demanding quick stabilization.
• Variable geology: Performs reliably in rocks where the strata conditions can change over short distances.
• Temporary support: Common in initial tunnel face stabilization.

Argentium’s expansion shell systems are tailored for convenience and adaptability across various tunnel environments.

3. Resin Grouted Rock Anchor Bolts

Overview

These bolts utilize a chemical resin to fill the void between bolt and rock. After the bolt is placed, a resin cartridge is broken and mixed inside the hole, quickly curing to form a powerful anchor.

Uses

• Rapid strength gain: Perfect for conditions where support must be set almost instantly.
• Damp or waterlogged tunnels: Resin’s chemical properties allow for use in environments where cement might not set well.
• Permanent reinforcement: Frequently used in high-value infrastructure projects demanding ultimate reliability.

Argentium ensures every chemical anchoring solution can withstand the toughest underground conditions.

4. Swellex Rock Bolts

Overview

The Swellex system consists of a flexible, sealed tube made of high-strength steel. Once inserted into the drilled hole, it is hydraulically expanded using pressurized water, conforming precisely to borehole irregularities and creating a uniform radial support.

Uses

• Highly fractured rock: Their flexibility and expansion ensure tight contact with the entire surface, providing 360-degree support.
• Dynamic environments: Swellex bolts are adept at adapting to shifting or settling rock masses.
• Projects with irregular boreholes: They grip even in uneven, varied rock faces.

Argentium’s Swellex bolts are recognized for both versatility and substantial load-bearing capability.

5. Refined Rolled Thread Bar Bolts

Overview

This robust, high-tensile steel bolt is furnished with coarse, rolled threads along its length for superior grip and easy tensioning. These can be either solid or used with grout for added strengthening.

Uses

• Hard rock conditions: Their strength excels in extremely tough strata.
• Permanent and long-term support: Ideal for large-diameter tunnels or where maximum load transfer is crucial.
• Seismic zones: Their robust design gives them a margin of safety where earth movements are a concern.

Argentium customizes these bars to suit diverse length and load requirements, meeting diverse geotechnical project demands.