Under the background of the vigorous development of the global construction industry, rock and soil anchoring technology plays an increasingly key role in all kinds of construction projects, and becomes the core element to ensure the stability and safety of the engineering structure. As a highly innovative and efficient cutting-edge solution in the geotechnical anchoring industry, a self-drilling anchor bolt provides a reliable guarantee for the construction of many complex geological conditions with its excellent performance and unique technical advantages. So, what exactly is a self-drilling anchor bolt?

A self-drilling anchor bolt is a new, simple, practical, and efficient anchoring solution for loose, easy-to-collapse soil and broken rock. Different from the conventional bolt, it does not need to drill in advance and can achieve drilling, grouting, and anchoring at the same time. When facing some challenging projects, self-drilling anchor bolts can greatly shorten the project delivery cycle and construction difficulty. 

In the above, we have a basic understanding of self-drilling anchor bolts. As a support material widely used in geotechnical engineering, mine support, and various underground engineering, self-drilling anchor bolt is gradually becoming an indispensable part of many engineering projects with its unique performance advantages. Next, we will introduce a self-drilling anchor bolt from four detailed aspects, and further reveal its powerful role and value in practical application.

What are the key components of a self-drilling anchor bolt?

 Self-drilling anchor bolt is composed of six key components: hollow anchor bar, coupler, nut, plate, drill bit, and centralizer. The close cooperation of each component makes the self-drilling anchor bolt maintain stability under various complex and changeable geological conditions, give full play to the role of anchoring, and meet the needs of various geotechnical anchoring projects.

Hollow anchor bar

The unique hollow hole design of the hollow anchor bar satisfies the development of washing operations, realizes the effect of grouting while drilling, and greatly improves the efficiency of construction. The hollow anchor bar adopts the design of a left-turn/right-turn thread. This design can be perfectly adapted to standard drilling tools, effectively ensuring the efficiency of the installation process. The hollow anchor bar has a large thread pitch and deep teeth, which can be cut arbitrarily and lengthened by connecting sleeves, so it is suitable for use in restricted and narrow spaces. The hollow anchor bar is rolled with high-quality alloy steel, and the bending torque and shear force are superior to the solid bar body compared with the solid bolt body, which can ensure that other components work together, and there will be no loosening of the connection and falling off.

At the same time, it is also conducive to ensuring the stability and reliability of the overall junction of the construction project and reducing safety hazards.

Drill bit

As the core component to achieve the functions of drilling and self-drilling, the drill bit plays an irreplaceable role in the self-drilling anchor bolt system. It belongs to disposable consumables, so it is also called a disposable drill, the design fully takes into account the diversity of geological conditions, and different models are adapted to different geological conditions, like all steel drill bits, generally suitable for sand, silt, percussion sandstone, pebble, compactly-filled earth, gravel, marl and other geology, and alloy drill bits, Generally suitable for hard clay, marl, chalk soil, medium dense shale, and other geology. Different geology has a corresponding type of drill bit, in order to ensure the efficient development of drilling operations. When the self-drilling anchor bolt is pushed to the specified depth according to the design requirements, the bit remains inside the hole.

Coupler

The main function of the coupler is to connect the two bolts together to achieve the length of the bolt while bearing torque and impact and promoting the energy transmission between each rod body. The design of each rod body has been accurately calculated, so that the connection between the two rods to maintain a strong seal, can minimize the loss of energy, to achieve the best energy transmission effect.

Centralizer

The centralizer needs to be set on the anchor rod to ensure that the anchor rod is in the center of the drilling hole so that the thickness of the grout is uniform, so that the anchor rod and the grouting body, the rock and soil body work better together so that the grout is evenly distributed, improve the grouting density and full degree, enhance the bonding force, prevent the anchor rod in the process of drilling and grouting and the hole wall friction collision loss and by the grout uneven erosion, prolong the service life.

Plate

There is a hole in the middle of the plate for the anchor rod to pass through, and it is installed between the exposed end of the anchor rod and the surface of the rock and soil mass. Let the tension of the bolt evenly disperse to the surface of the rock and soil body, avoid the local damage of the rock and soil body caused by the concentrated stress, and close contact with the rock and soil body, increase the friction and biting force, and enhance the effect of anchoring.

Nut

The nut is used for the end of the anchor rod and matches the external thread of the anchor rod. It is used with the cushion plate to connect and fix the cushion plate and the anchor rod to prevent relative displacement when the force is applied. During installation, the prestress of the anchor rod is increased by tightening, which suppresses the deformation of the rock and soil mass and improves the carrying capacity.

What is the working principle of self-drilling anchor bolts?

According to the workflow of the self-drilling anchor bolt, its working principle can be divided into three parts:

Drilling principle

The use of traditional drill rig and other equipment to provide power, and drive the hollow anchor bar directly into the rock formation, drilling will complete the hole operation, with no need to pull out the bolt, while drilling, will produce a large number of drilling slag, rod body unique design plays a key role, can effectively eliminate drilling slag, ensure the smooth and efficient drilling work.

Grouting principle

After the drilling, the cement slurry under the action of pressure flows out of the slurry hole of the drill bit and then fills the gap of the rock and soil body. When the slurry solidifies, it closely combines with the rod body and the surrounding rock and soil body to form an anchor solid, thus enhancing the cohesion and friction force of the rock and soil body, and significantly improving the strength and stability of the rock and soil body.

Anchoring principle

After the completion of drilling and grouting, it is necessary to install the backing plate and nut on the bolt construction which is exposed outside the construction face. When the rock mass is deformed due to factors such as the weight of the excavated building, the force generated by the deformation will be transferred to the nut through the plate in close contact with the rock and soil mass, and then transferred from the nut to the hollow anchor bar, and then to the anchor solid. The friction between the anchor solid and the rock and soil mass will produce a reverse anchoring force. This anchoring force can effectively prevent the continuous deformation of the rock and soil body, so as to ensure the stability of the entire supporting structure.

What are the applications of the self-drilling anchor bolts?

The Slope Stabilization Project

In slope stabilization projects, whether it is soil slope or rock slope, it can provide reinforcement support accurately according to different geological conditions; In the retaining wall structure, it provides a strong anchoring force for the retaining wall, preventing the retaining wall from displacing or collapsing due to lateral earth pressure; For the stability of the embankment and the reinforcement of the cutting, the self drilling anchor bolt also plays an important role in ensuring the safety and smooth flow of the road in various complex terrain and climate conditions. In addition, common ones are: slope stability, rockfall protection, and avalanche protection foundations.

The Foundation Project

In the foundation reinforcement project, it can successfully transmit the structural load to the foundation structure below, so as to effectively limit the deformation of the building. For the weak foundation or the foundation with hidden trouble of uneven settlement, the self-drilling hollow anchor can strengthen the soil through grouting, improve the bearing capacity of the foundation, and make it meet the bearing requirements of the building; For the reinforcement of old buildings,  self-drilling anchor bolt can make up for the deficiency of the original foundation, enhance the overall stability of the building and extend the service life of the building. In addition, there are also common applications such as anti-floating, anti-uplift foundation, sound wall foundation, beam anchoring, abutment foundation, coast protection, wind power, power transmission and transformation foundation.

The Underground Project

In tunnel and underground engineering, self-drilling anchor bolts also play an important role, especially in advance support.  Self-drilling anchor bolts can penetrate deep into the soil and carry out high-pressure grouting through the hollow structure. In the process of grouting, the slurry permeates and diffuses to the surrounding soil under the action of high pressure, and is closely combined with the soil, as if countless “steel bars” are formed in the soil, which strengthens the radial of the soil and greatly improves the strength and stability of the soil. In addition, it is also applied to a system support, roof support, lock foot support, palm surface reinforcement, tunnel end face support, and other application scenarios.

What are the advantages of self-drilling anchor bolts?

1. The variety of disposable bits is rich and suitable for different geological environments, the construction effect is better than that of ordinary bolts in all kinds of geotechnical conditions, especially in complex geological environments such as easy collapse geological conditions, the advantage is more obvious.

2. One-step operation of drilling, installation, and grouting can use different RIGS according to different application scenarios, which greatly improves production efficiency.

3. Compared with ordinary bolts, self-drilling bolts are not limited by existing bolt materials and drilling equipment, and the drilling depth is deeper, which can meet the needs of deeper drilling.

4. Suitable for narrow environment construction, the length of a single bolt can be cut or extended according to needs, and the flexibility is high.

5. The screw grouting machine is used in the drilling process, so that the slurry quickly fills the drilling hole and the surrounding rock and soil body, and is absorbed and solidified by the hole wall, which effectively guarantees the stability of the hole wall.

Summary

Self-drilling anchor bolt, a new anchoring material, provides an economical and reliable solution for some challenging geological conditions. With its unique “one-stop” operation advantage, it breaks through the limitations of traditional anchoring methods and integrates drilling, grouting, and anchoring. It is mainly used in slope engineering,foundation engineering, and tunnel and underground engineering. It is used to solve complex geological problems. In the future, with the continuous rise of the construction industry’s pursuit of engineering quality and efficiency, and the continuous emergence of various large-scale and super-large-scale projects, the self-drilling anchor bolt will expand a broader application space in the field of geotechnical anchoring by virtue of its own characteristics, lay a solid foundation for the vigorous development of the global construction industry, and help more “impossible” architectural miracles to rise.