As shallow mineral resources become increasingly depleted, mining operations are gradually shifting toward deeper excavation. In deep mining environments, challenges such as soft rock rheology, faulted fractured zones, and superimposed mining stress pose unprecedented difficulties for roadway support systems.

Traditional support methods are often time-consuming and inefficient. In highly fractured formations, boreholes collapse immediately after drilling, making it impossible to insert conventional anchor bolts. Even when installation is completed, ordinary bolts often fail to bond effectively with broken surrounding rock, resulting in a support system that provides little real reinforcement.

The emergence of self-drilling anchor bolts was specifically designed to address these critical industry challenges.

1. Working Principle of Self-Drilling Anchor Bolts

Unlike conventional anchor bolts, a self-drilling anchor bolt functions simultaneously as both drill rod and support element.

• The bolt body is made of seamless steel tubing with high tensile strength and yield capacity after special heat treatment.
• A carbide drill bit is attached at the front end, while extension couplings can be used at the rear.
• After drilling to the designed depth, the drill rod is not removed.
• High-pressure grout is injected directly through the hollow core, exiting through ports in the drill bit and permeating rock fractures.

This process forms a fully bonded reinforcement system along the entire bolt length, integrating the surrounding rock into a unified support structure.

2. Application of Self-Drilling Anchor Bolts in Underground Mines

2.1 Effective borehole formation in fractured zones

In fault zones, jointed rock masses, and loose soft rock, conventional drilling often leads to immediate borehole collapse due to stress release.

Self-drilling anchor bolts adopt a simultaneous drilling-and-supporting method:

• The drill bit breaks the rock while the bolt immediately follows to stabilize the borehole.
• High-pressure flushing media (water or air) is discharged through the hollow rod to reduce exposure time of the borehole wall.

This fundamentally solves the problem of borehole instability in fractured formations.

2.2 Controlling surrounding rock collapse

Roof strata in underground roadways are often highly fractured and structurally weak. Traditional bolts are passive systems that only bear load after deformation occurs.

In contrast, self-drilling anchor bolts:

• Inject grout that penetrates fractures and bonds loose rock blocks
• Transform fragmented rock into a continuous composite arch structure
• Convert surrounding rock from a load source into a load-bearing system

In practical applications, roadway deformation has been reduced from approximately 1500 mm to 300400 mm, representing a reduction of over 70%.

2.3 Advanced forepoling (canopy tube support)

For fault crossings and large-section intersections, self-drilling anchor bolts can be used as advanced support pipes.

By drilling ahead of the excavation face at an outward angle of 5°15°:

• A reinforced umbrella-shaped pre-support arch is formed after grouting
• Roof collapse risk during excavation is significantly reduced

This method eliminates multiple traditional steps such as rod withdrawal, resin cartridge installation, and re-drilling, reducing installation time per bolt by more than 50% in large-section roadways.

3. Advantages of Self-Drilling Anchor Bolt Systems

3.1 More than 50% time reduction

Traditional anchoring requires multiple steps: drilling, rod withdrawal, resin insertion, bolt placement, mixing, curing, plate installation, and pre-tensioning.

Self-drilling anchor bolts simplify the process to:

• Connect rod
• Drill to design depth
• High-pressure grouting
• Install bearing plate and tension

Installation time is reduced from 812 minutes per bolt to 35 minutes, improving efficiency by 60%70%.

3.2 Lower overall cost

Although unit material cost is higher, traditional systems in fractured rock often fail more than 50% of the time and require additional consumables such as casing pipes or secondary grouting.

Self-drilling systems eliminate:

• casing requirements
• separate grout pipes
• drill rod withdrawal

This reduces auxiliary material consumption by over 30%. Over time, maintenance and rework costs are significantly lower.

3.3 Adaptability to complex geological conditions

Self-drilling anchor bolts perform effectively in:

• weak rock formations
• fractured zones
• highly variable geological environments

Grouting materials and rod configurations can be adjusted based on field conditions, ensuring stable long-term support performance.

3.4 Higher safety performance

The system reduces manpower per cycle by 23 workers and minimizes operator exposure to hazardous zones. Reduced equipment switching and simplified procedures also significantly improve overall construction safety.

4. Case Study: A Gold Mine in Xinjiang, China

A gold mine project in Xinjiang encountered severe fractured rock conditions during roadway excavation. Conventional small pipe supports could not be inserted into pre-drilled holes due to collapse and instability.

This led to:

• low excavation efficiency
• high operational risk
• insufficient support reliability

The project later adopted a self-drilling forepoling system with support-before-blasting methodology.

Using R51 self-drilling anchor bolts, which provide high rigidity and drilling stability:

• Excavation and support efficiency improved significantly
• Daily advance rate increased from 1.21.5 m/day to 2.52.8 m/day
• Breakage of support elements and roof collapse risks were greatly reduced
• Material cost savings reached approximately 30%
• Overall project cost reduced by more than 40%

Conclusion

Self-drilling anchor bolts have become a critical solution in underground mining roadway support due to their efficiency, reliability, and adaptability.

However, due to complex geological variability in mining environments, system design must consider:

• equipment compatibility
• roadway dimensions
• operator skill level

Selecting a supplier capable of providing on-site technical support and full-system solutions is essential for successful implementation.

With extensive experience in self-drilling anchoring systems, Sinorock provides end-to-end services including solution design, product selection, equipment matching, and field guidance, supporting safe and efficient mining operations.

Categories

Mining, Tunneling in Rock, Underground Structures

Keywords

Self-Drilling Anchor Bolt, mining roadway support, fractured rock reinforcement