Application of Self-Drilling Anchor Bolts in IV and V Surrounding Rock Tunnels

Time:2025-12-16From:sinorock View:

In modern tunnel engineering and underground space development, surrounding rock support is crucial for ensuring construction safety and structural stability. Particularly in Grade IV and V surrounding rock environments, traditional support methods face significant challenges due to characteristics like fragmented rock, well-developed joints, and poor self-stability. Self-drilling anchor bolts (SDA) have emerged as a cutting-edge solution, offering numerous advantages in these complex geological conditions. This article explores the technical principles, application benefits, and engineering practices of self-drilling anchor bolts in Grade IV and V surrounding rock environments.

Geological Characteristics and Support Challenges

Grade IV Surrounding Rock Characteristics

Grade IV surrounding rock is typically fragmented, with well-developed structural surfaces and poor rock integrity. Key features include:

Moderate to low rock strength

Well-developed joints and fractures

Blocky or shattered rock structure

Short self-stability, ranging from hours to a few days

These conditions make the surrounding rock prone to local collapses and deformations, requiring precise and timely support.

Grade V Surrounding Rock Characteristics

Grade V surrounding rock is classified as weak, highly fragmented, and extremely unstable. Key features include:

Severe fragmentation, gravelly or soil-like texture

Very low strength

Highly developed joint and fracture systems

Near-zero self-stability

In addition, high ground stress, groundwater pressure, and expansive formations complicate construction and pose substantial challenges to support systems.

Limitations of Traditional Support Methods

Traditional anchor bolt support systems struggle in Grade IV and V environments due to several limitations:

Pre-drilling challenges: In fractured rock, holes often collapse, making it difficult to grout and anchor effectively.

Complex construction process: Traditional methods require multiple steps (drilling, hole cleaning, anchor installation, and grouting), which can be slow and ineffective in environments with short self-stability.

Self-Drilling Anchor Bolts: Key Technical Principles

Self-Drilling Anchor Bolts Working Principle

Structural Composition

Self-drilling anchor bolts integrate drilling, grouting, and anchoring into one system. The system consists of:

Hollow drill rod (serving as both anchor body and grout channel)

Drill bit (breaking rock and guiding installation)

Grouting pipeline (for grout injection)

Anchoring section (providing support to surrounding rock)

Working Principle

The construction process involves:

Drilling: A specialized drilling machine rotates the hollow rod, breaking the rock and forming a hole.

Grouting: Once the desired depth is reached, water is pumped through the rod for cooling, followed by grout injection to fill the hole.

Anchoring: The grout solidifies, turning the rod into a permanent anchor, creating an integrated support system.

Technological Innovations

The integration of drilling, grouting, and anchoring eliminates procedural transitions and reduces construction time by over 50% compared to traditional methods. This innovation also helps prevent hole collapse in fractured rocks, making it ideal for unstable formations.

Advantages of Self-Drilling Anchor Bolts in Grade IV and V Environments

Rapid Response and Timely Support

In Grade IV and V surrounding rock, quick stabilization is essential. Self-drilling anchor bolts allow immediate support after excavation, speeding up construction by 50% compared to traditional methods. This rapid response helps prevent rock deformation and collapse, crucial in short self-stability environments.

Strong Adaptability

Self-drilling anchor bolts are highly adaptable, effectively drilling and grouting through fragmented rock, weak interlayers, and water-rich formations. The system's ability to adjust drilling parameters ensures successful installation even in isolated or hard interlayers, making it ideal for complex geological conditions.

Reliable Anchoring Quality

Traditional anchor bolts often suffer from incomplete grouting, leading to weak anchoring. The hollow rod design of self-drilling anchor bolts ensures complete filling of the hole with grout, creating full-length bonding between the anchor and surrounding rock. Testing has shown that anchoring strength meets or exceeds design specifications, providing reliable support.

Minimal Disturbance to Surrounding Rock

Self-drilling anchor bolts use small-diameter drilling, minimizing damage to the surrounding rock structure. Additionally, the grouting process fills rock fissures, enhancing rock strength and improving its mechanical properties. This "drilling and grouting reinforcement" effect creates a more stable support system.

Engineering Case Studies

Mountain Tunnel Engineering

A highway tunnel project in a mountainous area passed through strata composed primarily of carbonaceous slate and shale, with surrounding rock grades ranging from IV to V. The surrounding rock exhibited poor self-stability after excavation, requiring immediate support. Self-drilling anchor bolts were used as the primary support method, combined with steel mesh and shotcrete.

Installation: Self-drilling anchor bolts were installed at lengths of 4-6 meters, spaced 1 meter apart in a staggered pattern.

Performance: Installation took only 15-20 minutes per bolt, significantly faster than the 40-50 minutes required for traditional bolts. The system effectively controlled surrounding rock deformation, keeping arch settlement and peripheral disturbance within design limits.

Mining Operations

In the Grade V surrounding rock of a gold mine, self-drilling rock bolts were used to reinforce the tunnel roof. The mine employed R32 rock bolts measuring 3 meters in length, with grouting performed using rapid-setting resin. Following installation, tunnel stability significantly improved, accident rates decreased by 70%, and the shear strength of the rock bolts reached 200 kN—far exceeding the required strength.

Conclusion

Self-drilling anchor bolts provide a highly effective solution for supporting Grade IV and V surrounding rock. Their integrated construction process, rapid response, and strong adaptability address the unique challenges posed by fractured and weak rock. Extensive engineering practice has demonstrated that this technology improves both construction efficiency and safety, providing significant technical and economic benefits.

With ongoing advancements, the application of self-drilling anchor bolts will continue to expand, especially in underground engineering and slope reinforcement projects. For future projects in complex geological conditions, prioritizing the use of self-drilling anchor bolts is recommended for optimal results.

Return The List