In modern construction projects, self-drilling anchor bolts are an efficient and convenient anchoring technology. They find extensive applications in slope support, tunnel reinforcement, underground engineering, and various other fields. Understanding the working principles of self-drilling anchor bolts in different application scenarios is of great significance to ensure their function safely and effectively.
The meaning of 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.
Working principles in different application scenarios
Slope support principle
In slope protection, the self-drilling anchor bolt is drilled into the slope body at a certain depth at a certain angle by a self-drilling anchor bolt drilling rig and then grouted by a grouting machine through the inner hollow channel of the pole body. The slurry fills the cracks in the rock and soil from the inside out through the slurry outlet hole of the drill bit, tightly enveloping the rod body. After completing the drilling and grouting process, plates and nuts are installed near the surface of the rock mass. Once the slurry solidifies, it forms an anchor body along with the rock bolt. When the rock and soil mass deforms, the force exerted on the pads and nuts is transmitted to the anchor. The anchor provides anchoring force through friction with the rock and soil mass, which can effectively prevent the deformation of the rock and soil mass and prevent the slope from sliding.
Foundation pit support principle
Self-drilling anchor bolts utilize a hollow anchor body with a threaded surface as a drill rod, with a drill bit installed at the end of the rod body. The drilling rig is employed to drive the rod body into the ground, after which grout is injected into the ground through the center hole of the rod body. This results in the anchor rod body being enveloped by cement mortar or a cement mortar body, which makes contact with the surrounding soil along the rod body and forms a binding body, creating an anchoring effect. Under the condition that the soil deforms, the rock bolt is passively stressed through the bonding friction force on the contact surface with the soil and mainly restrains, strengthens, or stabilizes the soil through tension.
Tunnel advance support principle
The self-drilling pipe shed can solve the construction problems of hole collapse after drilling in IV and V level surrounding rock conditions, drill stuck, and the inability to insert ordinary flower pipe sheds after drilling. The self-drilling pipe shed has strong toughness and small radial plastic deformation of the surrounding rock. After support, a load-bearing arch is formed, which provides effective reinforcement and ensures the safety of tunnel excavation and initial support. Compared with the traditional pipe shed support construction, the self-drilling pipe shed support construction completes the two processes of drilling and grouting at one time, more than doubling the construction efficiency, convenient grouting, and good grouting effect, which plays a leading role. The role of support can effectively reduce surface settlement and prevent surrounding rock collapse.
Working principle of prestressed self-drilling anchor bolt
Self-drilling prestressed anchor bolt technology is a technology that buries tension rods (self-drilling anchor bolts) into the ground to reinforce structures. It provides resistance to the structure to withstand external loads, creates a compressive stress zone on the anchoring stratum (reinforcing the rock), and enhances the strength of the stratum. Self-drilling prestressed anchor bolt technology uses rock bolts to connect structures with rock and soil to form an anchoring structure that increases the rock mass’s pressure-bearing capacity and shear resistance.
Application advantages of self-drilling anchor bolts
High construction efficiency
Self-drilling anchor bolts integrate drilling, grouting, and anchoring, simplifying the construction steps and shortening the construction period, and are highly efficient, 4-5 times that of steel bars, anchor cables, and other processes.
Good anchoring effect
Simultaneous drilling and grouting ensure good cement slurry bonding and anchoring effects.
Strong equipment adaptability
Self-drilling anchor bolts can be adapted to DTH drilling rigs, anchoring drilling rigs, rock drilling rigs, and other equipment.
Precautions for self-drilling anchor bolt construction
Choose the appropriate self-drilling anchor bolt
Select appropriate self-drilling anchor bolt specifications and parameters according to project requirements and stratigraphic conditions to ensure the support effect of the anchor.
Select drill bits according to geology
Self-drilling anchor bolts are equipped with drill bits made of different materials depending on the geological conditions. The selection should be according to geological survey reports and design requirements. For instance, in conglomerate layers with numerous pebbles and high hardness, it is advisable to use alloy drill bits during construction.
Selection of drilling rig
Not all drilling rigs on the market can drill self-drilling anchor bolts. It is necessary to use modified drilling rigs or special drilling rigs for self-drilling anchor bolts to carry out the construction, and it is also required to consider the environment of the construction site and the construction conditions.
Maintain appropriate drilling speed
During the drilling process, it’s essential to maintain appropriate drilling speed and grouting pressure to prevent excessive disturbance and damage to the formation.
Grouting cement requirements
Rock bolt grouting should adopt pure cement slurry or 1:1 mortar. When using mortar, ensure that the particle size of the sand does not exceed 1.0mm, and control the water-cement ratio within the range of 0.4-0.5. It enables the slurry to thoroughly penetrate the gaps in the rock, enhancing the anchoring effect.
Conclusion
As an efficient and convenient support product, self-drilling anchor bolts have demonstrated their unique advantages in various application scenarios. Understanding its working principle and application advantages is of great significance to ensure the stability and safety of the project. With the continuous development of science and technology, self-drilling anchor bolt technology is also constantly innovating and improving. In the future, we can anticipate the emergence of more efficient, intelligent, and environmentally friendly self-drilling anchor bolt technology, which will offer robust support for the development of slope support, tunnel reinforcement, underground engineering, and other fields.
