1. Self Drilling Anchor System
1.1 What is a Self-Drilling Anchor System?
The self-drilling anchor system is primarily composed of a hollow threaded anchor rod with a sacrificial drill bit, and various other accessories. This system enables simultaneous drilling, anchoring, and grouting operations to be performed.
1.2 The advantages of the Self-Drilling Anchor system
Due to the unique construction of self-drilling anchor system, it exhibits the following features during anchoring construction:
- 1.2.1 High Construction Efficiency: The self-drilling anchor system integrates drilling, grouting, and anchoring into a single process, significantly reducing construction time.
- 1.2.2 Suitable for Various Ground Conditions: After drilling, the self-drilling anchor bolt does not need to be removed from the drilled hole, avoiding the collapse of the hole that can occur with conventional anchor systems. This feature makes it suitable for various ground structures and significantly reduces construction difficulty.
- 1.2.3 Strong Adaptability: The self-drilling anchor bolt comes in multiple specifications, and the entire rod is covered with threads. It can be cut or extended at any position along the anchor bolt, making it suitable for various construction conditions.
- 1.2.4 High Anchoring Force: The self-drilling anchor bolt is completely covered with threads, ensuring better integration with grout material.
- 1.2.5 Ensuring Grouting Quality: During grouting, the grout is injected from the bottom hole of the anchor bolt, travels upward through the hollow rod body, and exits at the front end of the anchor bit. It then returns to the rear end, ensuring complete filling of the voids around the anchor bolt, consolidating the rock mass, and guaranteeing the quality of grouting and anchoring. 1.2.6 Convenient Construction: Compared to conventional anchor construction, the self-drilling anchor system reduces the need for drilling, installing anchor rods, and placing grout pipes, simplifying the construction process.
- 1.2.6 Convenient Construction: Compared to conventional anchor construction, the self-drilling anchor system reduces the need for drilling, installing anchor rods, and placing grout pipes, simplifying the construction process.
2. Development of Self-Drilling Anchor System
Anchoring technology is an important branch in the field of modern geotechnical engineering. It is a structurally simple active support system that maximizes the integrity and stability of the surrounding rock mass. It effectively controls deformation, displacement, and crack development in the rock mass while utilizing the inherent support capacity of the rock mass. In other words, it transforms the rock mass from being loaded to being a load-bearing element and shifts from passive support to active support. In geotechnical engineering construction, anchoring involves the use of tools capable of withstanding strong tensile stress to enter the rock mass, aiming to adjust and enhance the strength and stability of the rock mass. The tool used for this construction is known as an anchor bolt.
Self-drilling anchor system is one type among various anchor bolt systems. In the 1980s, addressing the issue of slow construction progress due to complex geological conditions in large underground projects, MAI International GmbH from Austria, specializing in the development and sale of geotechnical anchoring technology and specialized equipment, introduced the New Austrian Tunneling Method (NATM). As part of this method, they designed a new type of anchor system that combines drilling, grouting, and anchoring functions, ensuring fast anchoring in fractured rock layers, soft soil layers, and geologically complex sections. This marked the introduction of the initial self-drilling anchor system. Initially, self-drilling anchor system was primarily developed for mining and tunneling projects. With the advancement of technology and a deeper understanding of the anchoring effect on rocks, self-drilling anchor system has found wider applications in other fields such as civil engineering, geotechnical engineering, and slope reinforcement. The use and market demand for self-drilling anchor system has been continuously growing, quickly establishing them as high-quality, efficient, and fully functional anchor bolt products. Meanwhile, different manufacturers have contributed to the innovation and improvement of self-drilling anchor systems, resulting in the formation of two industry standards for self-drilling anchor bolts: MAI and ISCHEBECK TITAN, established by respective companies.
3. Application of self-drilling anchor system
3.1 In tunnel engineering
The self-drilling anchor system serves as a distinctive anchoring system that caters to the requirements of tunnel safety and rapid construction. It finds application in tunnel support, pre-support, and related areas. By utilizing self-drilling anchor bolts to reinforce the rock mass, the self-drilling anchor system effectively fulfills its role in providing support, enhancing the load-bearing capacity of the surrounding rock, ensuring the overall stability of the rock mass, and preventing collapse.
3.2 In slope stabilization projects
The anchor bit at the front end of the self-drilling anchor bolt can easily penetrate various rock formations under the action of a typical rock drilling machine. The self-drilling anchor bolt can be used as a drill rod to complete the drilling process in conjunction with the drill bit. After the drilling is completed, the anchor bolt does not need to be removed and can serve as a grouting conduit. By fully filling the voids and securing the fractured rock mass, the high-strength plate and nut can evenly distribute the stress from the deep surrounding rock to the surrounding rock, achieving mutual support between the surrounding rock and the anchor bolt.
3.3 In soil nailing applications.
The unique advantages of the self-drilling anchor bolt allow it to be used as an alternative to conventional soil nails in construction. After drilling to the specified depth using the self-drilling anchor bolt system, the self-drilling anchor bolt and the anchor bit remain permanently embedded in the soil. Grouting is then performed through the hollow body of the self-drilling anchor bolt, effectively transforming it into a small-diameter anchoring pile for reinforcing the rock mass. The system exhibits excellent tensile and compressive anchoring strength, minimal displacement, simplified construction, and provides a stable supporting structure.
3.4 In foundation engineering.
The self-drilling anchor bolt can be transformed into a prestressed anchor rod by applying preload through the plate and nut connected to the anchor bolt. This prestressed anchor bolt is used for various applications such as slope stabilization, anti-floating measures, and foundation anchoring.
Nowadays, with the continuous improvement in equipment mechanization and increasing demands for construction efficiency and quality, the usage of self-drilling anchor systems has significantly increased in various construction sites, including anchoring support, slope remediation, excavation wall protection in foundation pits, large underground mine tunnels, and large-scale underground projects
The self-drilling anchor system primarily consists of components such as self-drilling anchors bolt, Self Drilling Anchor drill bits, Self Drilling Anchor coupling sleeves, Self Drilling Anchor plates, Self Drilling Anchor nuts, Self Drilling Anchor Centralizers, Self Drilling Anchor adapters, and other accessories. The entire self-drilling anchor system product line is designed as disposable consumables
4. Structure of Self-Drilling Anchor System
4.1 Self-Drilling Anchor Bolt
The self-drilling anchor bolt uses thick-walled seamless steel pipes produced according to API standards as raw materials. The steel pipes are processed using cold rolling to form R threads that comply with ISO standards or T threads that meet company standards. The cold rolling process allows for more precise thread formation on the surface of the self-drilling anchor bolt, while also refining the grain structure of the steel pipe and increasing the yield strength of the anchor bolt. To protect the anchor body from environmental damage and corrosion in soil and rock, the surface of the anchor body can be further protected through hot-dip galvanizing or epoxy resin coating.
| Size | O.D (mm) | I.D (mm) | Sectional Area (mm² ) | Ultimate Load (KN) | Yield Load (KN) | Agt(%) | Weight (kg/meter) | |
| R25 | R25N-14 | 25.0 | 14.0 | 290 | 200 | 150 | >10% | 2.30 |
| R32 | R32L-22 | 32.0 | 22.0 | 350 | 210 | 160 | >10% | 2.80 |
| R32N-21 | 32.0 | 21.0 | 370 | 280 | 230 | >6% | 2.90 | |
| R32N-18.5 | 32.0 | 18.5 | 430 | 280 | 230 | >10% | 3.40 | |
| R32S-17.5 | 32.0 | 17.5 | 440 | 360 | 280 | >6% | 3.50 | |
| R32S-15 | 32.0 | 15.0 | 520 | 360 | 280 | >10% | 4.10 | |
| R32SS-14 | 32.0 | 14.0 | 520 | 405 | 350 | >10% | 4.10 | |
| R38 | R38N-21 | 38.0 | 21.0 | 620 | 500 | 400 | >6% | 4.90 |
| R38N-19 | 38.0 | 19.0 | 700 | 500 | 400 | >10% | 5.50 | |
| R38S-18 | 38.0 | 18.0 | 700 | 560 | 460 | >10% | 5.50 | |
| R51 | R51L-38 | 51.0 | 38.0 | 760 | 550 | 450 | >6% | 6.00 |
| R51L-36 | 51.0 | 36.0 | 970 | 550 | 450 | >10% | 7.60 | |
| R51N-36 | 51.0 | 36.0 | 970 | 800 | 630 | >6% | 7.60 | |
| R51N-33 | 51.0 | 33.0 | 1070 | 800 | 630 | >10% | 8.40 | |
| R51S-30 | 51.0 | 30.0 | 1160 | 930 | 730 | >10% | 9.10 | |
| T76 | T76N-49 | 76.0 | 49.0 | 2100 | 1600 | 1200 | >6% | 16.5 |
| T76S-45 | 76.0 | 45.0 | 2420 | 1900 | 1500 | >6% | 19.0 | |
| T30 | T30-11 | 30.0 | 11.0 | 420 | 320 | 260 | >10% | 3.30 |
| T30-14 | 30.0 | 14.0 | 370 | 275 | 220 | >10% | 2.90 | |
| T30-16 | 30.0 | 16.0 | 340 | 245 | 190 | >10% | 2.70 | |
| T40 | T40-16 | 40.0 | 16.0 | 900 | 660 | 525 | >10% | 7.10 |
| T40-20 | 40.0 | 20.0 | 710 | 540 | 425 | >10% | 5.60 | |
| T52 | T52-26 | 52.0 | 26.0 | 1270 | 930 | 730 | >10% | 10.0 |
| T73 | T73-56 | 73.0 | 56.0 | 1380 | 1035 | 830 | >6% | 10.8 |
| T73-53 | 73.0 | 53.0 | 1780 | 1160 | 970 | >6% | 14.0 | |
| T73-45 | 73.0 | 45.0 | 2230 | 1600 | 1270 | >6% | 17.5 | |
| T73-35 | 73.0 | 35.0 | 2700 | 1865 | 1430 | >6% | 21.2 | |
| T103 | T103-78 | 103.0 | 78.0 | 3180 | 2270 | 1800 | >6% | 25.0 |
| T103-51 | 103.0 | 51.0 | 5600 | 3660 | 2670 | >6% | 44.0 |
4.2 Self-Drilling Anchor Bit
During the construction process of using self-drilling anchor tools, it is necessary to select different types of self-drilling anchor bits based on different geological structures and rock types. The main types of self-drilling anchor bits are as follows.
- 4.2.1 Self-Drilling Anchor Cross Bit
EX: Fully machined cast or forged all-steel cross drill bit, practical through heat treatment with quenching and hardening, primarily used for soft rock construction situations. It is a commonly used type of self-drilling anchor bit.
EXX: Tungsten Carbide cross drill bit with hard alloy inserts at the top. Primarily used for soft rock and medium-hard rock conditions.
- 4.2.2 Self-Drilling Anchor Button Bit
ES: Fully machined cast or forged all-steel button drill bit. The full steel button drill bit is primarily used for medium-depth anchoring in fractured rock formations of soft rock and medium-hard rock.
ESS: Tungsten Carbide button drill bit with hard alloy teeth inserts on the top. Due to the Tungsten Carbide on the drill bit head, this type of drill bit can be used for construction in medium-hard rock formations. It features fast penetration, smooth drilling, and fewer tendencies to get stuck.
- 4.2.3 Arch Self drilling anchor bit
EC: Asymmetric all steel arch self drilling anchor drill bit formed through forging, used for unconsolidated soil and small stones, with faster penetration in soft rock.
ECC: Tungsten Carbide inserts embedded in the drill bit head, used for anchoring construction in medium-hard fractured rock formations.
- 4.2.4 Three Cutters self-drilling anchoring drill bit
EY: All steel three cutters drill bit, formed by forging or casting, used as an anchoring drill bit for loose soil and rock.
EYY: Tungsten Carbide three cutters self-drilling anchoring drill bit, with Tungsten Carbide inserts, suitable for anchoring situations in medium-hard rock formations.
4.3 Self-Drilling Anchor Coupling Sleeve and Nut
The self-drilling anchor coupling sleeve is used to connect the anchor bolt for extension to the designed drilling depth. The coupling sleeve is typically made of seamless steel pipe and processed to have an R or T thread. It undergoes heat treatment to ensure its comprehensive mechanical strength is higher than that of the self-drilling anchor bolt.
The self-drilling anchor nut is used to secure the entire self-drilling anchoring tool, ensuring the entire anchoring system is fixed at the specified anchoring point. It is commonly available in hexagonal and spherical types.
4.4 Self-Drilling Anchor Plate
The self-drilling anchor plate is used to secure the anchor point and is typically designed in domed type and solid type. They are used for anchoring rock layers in different geological structures according to the requirements of the project. The plate is manufactured through cold stamping process.
4.5 Self-Drilling Anchor other accessories
Self Drilling Anchor Centralizer: Used to ensure that the anchor bolt is positioned in the center of the drilled anchoring hole, while ensuring that the grout can fully envelop the entire anchor bolt body.
Self-Drilling Anchor Adapter: It has internal and external threads with different sizes, facilitating the connection between anchor bolt and anchor bit with different thread sizes.
Grout stopper: Made of rubber material, it provides a certain sealing effect, maintaining a certain pressure for grouting to fully fill the voids in the surrounding rock, achieving complete grouting and compactness.
5. Construction Process of Self-Drilling Anchoring Drill Tools
- 5.1 Before use, check whether the anchor drill bit and anchor bolt are ventilated. If there is any blockage, it should be cleared before use.
- 5.2 Connect the anchor drill bit and anchor bolt, drill rig and shank adapter, coupling sleeve and shank adapter, anchor bolt and coupling sleeve, etc.
- 5.3 Align the self-drilling anchor system with the designated anchor hole position. The rock drilling machine should be supplied with air or water first before drilling. When drilling in fractured rock, the water holes in the drill bit are prone to blockage. Therefore, during drilling, the drilling speed should be slowed down, with more rotations and less impact. Pay attention to the water flow from the drill hole. If there is blockage in the water holes, retract the self-drilling anchor system, repeatedly clean the holes to ensure water holes are unobstructed, and then slowly advance until the design depth is reached.
- 5.4 When reaching the design depth, flush the hole with water or air, and check if the holes on the anchor bit are clear. Then remove the anchor bolt from the drilling machine, and expose the anchor bolt as required by the design.
- 5.5 Insert the grout stopper through the exposed end of the anchor bolt to seal the hole for grouting. If the grouting pressure is high or the surrounding rock is highly fractured, grout can also be used for hole sealing.
- 5.6 Quickly connect the anchor bolt, grouting pipe, and pump with quick couplings, and start the grouting pump. The entire process should be continuous without interruptions and must be completed in one go.
- 5.7 After the grouting is completed, install the plate and nut.
6. Conclusion
In conclusion, the self-drilling anchoring tool, as an integrated solution for drilling, grouting, and anchoring, demonstrates significant advantages in complex geotechnical anchoring projects. It eliminates the need for casing or separate installation of anchor bolt, providing immediate support to the rock mass after excavation and effectively protecting its inherent strength, preventing rock loosening and deformation, thus enhancing the stability of geotechnical engineering.
Furthermore, the self-drilling anchor tool ensures thorough encapsulation of the bolt with grout after grouting completion. With its refined seamless steel pipe construction, it greatly enhances the product’s resistance to corrosion and ensures excellent durability during engineering applications. These characteristics contribute significantly to the reliability and long-term performance of the self-drilling anchoring tool in harsh environments.
By utilizing the self-drilling anchor tool, safer and more efficient construction can be achieved in anchoring projects. The innovative design and reliability of the self-drilling anchor tool make it an indispensable key tool in the field of geotechnical engineering, providing stability and reliability assurance for various engineering projects under different geological conditions.
