What is A Self-drilling Anchor Bolt?

Table of Contents

The self-drilling anchor bolt system is an anchoring system carefully designed according to different sites, geology, and usage conditions, and has the characteristics of high efficiency, reliability, and convenient construction. The system can ensure the anchoring effect in various field formations. Therefore, it is an efficient and economical geological support material with broad application prospects and market demands.

What is a self-drilling anchor bolt?

self-drilling anchor bolt

A self-drilling anchor bolt is a product that can integrate drilling, grouting, and anchoring. Its construction process is simple, the construction efficiency is high, the anchoring effect is good, and there is no need to worry about the problem of hole collapse. Therefore, it applies to a wide range of geological conditions, such as siltstone, miscellaneous fill, strongly weathered rock, pebble layer, and conglomerate layer.

Self-drilling anchor bolts are mainly used in tunnel and underground engineering, slope stabilization engineering, ground and foundation engineering, such as various slope support, foundation support, tunnel pipe umbrella support, foundation support of transmission towers or wind power towers, existing buildings and structures repair and reinforcement. It is used for temporary support and permanent support in the pre-project period, which can effectively enhance itself stability of soil and rock, and has become an indispensable material in geotechnical anchorage engineering.

Composition of self-drilling anchor bolt

Composition of self-drilling anchor bolt

Self-drilling anchor bolt consists of six major accessories, a hollow anchor bar, a drill bit, a coupler, a plate, a nut, and a centralizer.

Hollow anchor bar

Hollow anchor bar

It combines an anchor rod with a drill pipe and has the dual function of drilling and grouting. The hollow anchor bar is made of seamless steel pipe of high tensile alloy steel, and the tensile strength and yield strength can meet various complex geological conditions according to the design requirements. Additionally, it features continuous R thread and T thread along its body for easy cutting and connection during construction.

Drill bit

Drill bit

The drill bit is made of wear-resistant metal, and has flush hole. The selection of the appropriate model according to the rock and soil conditions. Commonly used drill bits include hardened cross-cut drill bits, tungsten carbide cross-cut drill bits, clay bits, hardened button drill bits, and tungsten carbide button drill bits.

Coupler

Coupler

The coupler is a part extensioning anchor bar, and it is of equal strength to the hollow anchor bar. Two rods can be connected seamlessly by the coupler, and there will be no grout leakage when grouting.

Plate

Plate

The plate is installed at the tail of the anchor bar, between the nut and the rock formation. There are two shapes: domed and flat plates. Domed plates are generally used in soil nail applications, while flat plates are used in micropile applications.

Nut

Nut

The nut is a device that has internal threads, which transmit the anchoring force of the hollow anchor bar to the plate and lock it in place. One end of the nut has a arc surface. When there is a slight angle between the plate and the rod, it can fit with the plate to ensure proper force transmission. If the angle is large, you can choose a domed nut or add a domed washer. Cooperating with the hollow anchor bar, they provide equal strength and the effect of preventing rock mass deformation.

Centralizer

Centralizer

The centralizer is a component used to realize the centering of the hollow anchor bar in the hole, which is installed on the hollow anchor bar in front of the coupler and realize the thickness of the grouting layer not less than 20mm. Using centralizer can ensure the uniform thickness of the grout around the rod during  construction and enhance anchoring effect.

Advantages of self-drilling anchor bolt systems

  • Strong adaptability of equipment and can be adapted to down-the-hole drills, anchor drilling rigs, rock drilling rigs, etc.
  • Diversified drilling methods, depending on the geology, rotary drilling, or rotary impact drilling.
  • The rod body is made of alloy steel, which can be used as a drill rod during drilling and as an anchor rod during anchoring.
  • All-thread rod design, convenient for any extension and cutting, also suitable for narrow places construction.
  • The rod can be extended by coupling sleeve and can achieve equal strength with the rod.
  • The hollow design of the rod can realize synchronous drilling and grouting.
  • Synchronous drilling and grouting, good anchoring effect.
  • It can realize the effect of rotary grouting, improve soil mass, fill cracks, consolidate rock mass and soil layer, and have good grouting diffusion radius and reliable anchoring quality.
  • Low comprehensive cost, close to steel, anchor cable, etc.
  • High efficiency, short construction period, 4-5 times that of steel bars, anchor cables, etc.
  • Long drilling depth, 3-40m depending on different product series.

Self-drilling anchor bolt construction process

  • Preparation before construction: check whether the functions of the drilling rig are proper, whether the drill bit and hollow anchor bar are damaged, whether the hollow anchor bar is smooth, etc. After ensuring that there are no problems, screw the hollow anchor bar to be used with the drill bit.
  • Drilling and grouting: connect the hollow anchor bar and grouting pipe to the drilling rig using the rotating grouting adapter, and conduct grouting while drilling to achieve simultaneous completion of drilling and grouting.
  • Extension of hollow anchor bar: if the length of a single self-drilling anchor bolt cannot reach the intended drilling depth, a coupler can be utilized to extend its length, ensuring it meets the design requirements.
  • Install plates and nuts: after grouting is completed, install plates and nuts in sequence on the part of the self-drilling anchor bolt exposed outside the rock body close to the construction surface to ensure the anchoring effect.

Application scenarios of self-drilling anchor bolts

Slope engineering

In transportation, water conservancy, hydropower, and urban geotechnical slope projects, high-strength self-drilling hollow anchor bars and full-length adhesive are generally used for the protection of high slopes with an excavation height greater than 30m, especially ultra-high slopes exceeding 100m. The reinforcement method combined with knot anchors reinforces the system and parts to maintain slope stability.

Tunnels and underground engineering

In tunnels and underground cavern projects, shotcrete support, that is, self-drilling hollow anchor bars, system mortar anchors, and reinforced shotcrete reinforcement methods, has become a frequent method to maintain the stability of the surrounding rock. Using this reinforcement method can effectively reduce the subsidence of the vault and the displacement of the side walls, ensure the stability of the cavern, and ensure the safety of personnel and property during project construction.

Coal mining engineering

In coal mine construction, self-drilling hollow anchor bars or self-drilling hollow bar anchors and shotcrete support are mainly used to reinforce the surrounding rock.

Ground and foundation Engineering

In urban foundation pits, self-drilling hollow anchor bars are also very common as the support structure of pile foundations. Usually, in foundation pit engineering, there are high requirements on the ultimate pullout force and drilling depth of rock bolts. The ultimate pullout force of large-diameter self-drilling hollow bar anchors can reach 1900kN, ensuring the stability of the foundation pit and the safety of the superstructure.

Water conservancy and hydropower dam engineering

In dam projects, employing self-drilling hollow anchor bars to secure the dam body to the bedrock can strengthen or raise the dam body without disrupting operations, resulting in significant cost savings in construction. As dams must withstand floods, the rock bolts that reinforce them usually have a higher design tension value.

Anti-floating project

In basement anti-floating projects, self-drilling hollow anchor bars are used as anti-floating anchors, which can improve the utilization of soil strength and the durability of rock bolts. There are various types of anti-floating rock bolts, including concentrated point arrangements, concentrated linear arrangements, and even surface arrangements.

Conclusion

As an essential supporting structure, self-drilling anchor bolts have promising application prospects in the fields of geotechnical engineering and underground engineering. By delving into a comprehensive understanding of self-drilling anchor bolts, we can adeptly apply them, furnishing a robust assurance for the safe, stable, and efficient execution of projects. Concurrently, as science and technology progress incessantly and engineering requirements evolve, self-drilling anchor bolts will persist in development and innovation, thereby making substantial contributions to future engineering constructions. We have reason to believe that in the days ahead, self-drilling anchor bolts will become more advanced, efficient, environmentally friendly, and intelligent, offering stronger support for human engineering construction.

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