In the field of geotechnical engineering such as foundation reinforcement, tunnel construction, and slope stabilization, self-drilling anchor bolt has become the core solution of modern anchoring engineering and plays an irreplaceable role by virtue of its unique technical advantages of integration of “drilling, grouting and anchoring”.
As the key component of the self-drilling anchor bolt system, the performance of the drill bit plays a decisive impact on the drilling efficiency, hole quality and the economy of the project. The efficient drilling efficiency can greatly shorten the construction period, and good hole quality is the foundation to ensure the stability of the project. Therefore, it is very important to choose a suitable drill bit.
This article will conduct an in – depth and systematic analysis from these three key dimensions, namely the function of the drill bit, classification and selection methods, on how to accurately select the appropriate drill bit according to different geological conditions, so as to provide practical references for relevant engineering practices.
Introduction of drill bit
Under normal circumstances, the common drill bit mainly serves the coal mine roadway support scene, some of which work together with Top hammer rock drilling tools and DTH drilling tools, and some are specially adapted to the use of rock bolts.
The drill bit matching with the rock bolts has a relatively conventional workflow.
After the completion of the drilling task, the operator needs to use a specific tool to pull it out of the hole in accordance with the standard process for subsequent reuse or maintenance.
This mode of operation is more common in the traditional drilling construction process. However, the drill bit of the self-drilling anchor bolt has a unique design and functional positioning. As the core component of the self-drilling anchor bolt drilling function, it is closely combined with the rock bolts in the drilling process to form an organic whole. When the drilling operation is finished, it will not be pulled out like the ordinary drill bit, but directly left in the hole.
This design not only simplifies the construction process, and reduces the time loss and equipment wear caused by repeated insertion and removal of the bit, but more importantly, it can immediately participate in the subsequent anchoring link, providing stable connection and support between the anchor rod and the hole wall, greatly improving the anchoring effect and engineering quality, and becoming an important embodiment of modern anchoring engineering technology innovation.
Classification of drill bit
In the above article, we also understand that the choice of drill bit plays a decisive role in construction efficiency and quality. There are five types of common self-drilling anchor bolt bits, each of which has its own unique advantages and is suitable for different geological conditions. Next, we will analyze the differences between these five kinds of drill bits from the aspects of drilling characteristics and applicable geology.
Hardened cross-cut drill bit
Forged from monolithic steel, the drill bit with a cross cut structure has excellent rotary drilling performance. In loose deposits such as mud, sand, and gravel soil, the bit can quickly cut soil when rotating, and the drilling process is smooth. In the face of weak soil such as chalk soil and lime soil, it can also rely on its own structure to effectively transmit torque and achieve efficient drilling. In artificially filled areas, the hardened cross-cut drill bit can easily cope with complex fillings and maintain stable drilling. Because of its simple structure and low production cost, construction under matching geological conditions is not only efficient but also can significantly reduce costs.
Tungsten carbide cross-cut drill bit
On the basis of a cross-shaped steel body, the cutting edge is inlaid with carbide to make it capable of both rotary and impact drilling. In the gravel stratum with large pebbles, the ordinary drill bit eaily stuck, but the cross alloy drill bit can use the impact to break the pebbles, cooperate with the rotary cutting, and drill smoothly.
In the rock stratum with crack development, the drill bit can break the rock along the crack impact and expand the drilling hole. In the face of unreinforced concrete, the carbide cutting edge can be effectively cut to ensure the quality of the drilling.
Clay bit
Unique spiral blade with wide cutting edge design, making it a “Nemesis” for soft soil layers. In clay and soft soil, the clay bit can quickly stir the soil and discharge it out of the hole to achieve efficient drilling. In the sand and gravel layer, the mud drill bit has a large slag discharge space to avoid clogging. Mixed fill and clay areas are its “best battleground”, where larger holes can be drilled at a relatively low cost.
Hardened button drill bit
Spherical teeth evenly distributed on the surface are its “secret weapon”, giving the drill bit strong impact properties. In the broken formation, the hardened button drill bit can effectively impact the broken rock and open up the drilling channel. Soft sandstone, and limestone, such as the moderate hardness of the rock, the repeated impact of the hardened button drill bit can rapidly break rock. In compact or consolidated soil, the impact can destroy the soil structure and facilitate drilling. In soft rock, it can also rely on the impact advantage, stable drilling, and ensure the construction progress.
Tungsten carbide button drill bit
Alloy material design, suitable for rotary and impact drilling, excellent performance in soft to medium hard weathered rock. Stonewall, gravel, and other strata, ball teeth can break hard stones, and alloy material to ensure the drill bit is usable. Broken rock, a large pebble area, can be through impact rotation, or efficient drilling. In mudstone, schist, volcanic rock, and other weathered rocks, tungsten carbide button drill bit can easily cope with complex geology by virtue of their own performance, and the hole formation efficiency is higher than that of ordinary bits.
Choice of drill bit
After an in-depth understanding of the characteristics of the five common self-drilling anchor bolt bits and the applicable geological conditions, how to accurately select the drill bit has become the key to ensuring the smooth progress of the project.
Next, we will deeply analyze the selection method of the drill bit from three key perspectives: rock hardness, construction rock type, and rock weathering degree.
Select drill bits according to rock hardness
Rock hardness and compressive strength are the key factors that can not be ignored when selecting the drill bit of the self-drilling anchor bolt, They are closely related and together determine the difficulty of drilling operations. Rock hardness, directly reflects the difficulty of drilling rock, when the drill bit and rock layer contact, it is actually the drill bit cutting structure, and rock hardness launches a “contest”.
In actual construction, low-hardness rock is suitable for the selection of relatively simple structures of the drill bit, such as the tungsten carbide cross-cut drill bit, which can rely on its own structural characteristics, in mud sand, chalk soil, and other low-hardness geology of rapid cutting, efficient drilling.
In the face of hard rocks, it is necessary to have a hardened button drill bit with a hard cutting edge and strong impact performance of the drill bit, through high-frequency impact and rotary cutting, to overcome the high strength resistance of the rock, to achieve efficient drilling, to ensure the construction progress and quality.
Selection based on construction rock type
The construction environment is complex and diverse, and the solidity coefficient and density of rocks in different regions are very different, which requires that the rock type be accurately confirmed before construction, and then the most suitable self-drilling anchor bolt drill bit must be matched. Uniaxial compressive strength (UCS) varies significantly among different types of rock. In order to improve drilling efficiency, it is important to accurately determine the maximum compressive stress that rock can bear before failure under uniaxial compression load.
For example, in the sandstone formation with fissure development, due to poor rock integrity, it is more appropriate to choose a tungsten carbide cross-cut drill bit, which can not only use rotary cutting to break the rock but also use the impact to deal with the fissure, to ensure the stability and perpendicularity of the drilling. In limestone, such a relatively homogeneous rock, a hardened button drill bit with its impact performance, can effectively break the rock, and improve the drilling speed.
Reference rock weathering degree selection
The degree of weathering of rocks can be subdivided into five levels: unweathered, breezy, moderately weathered, strongly weathered, and fully weathered. With the gradual deepening of the weathering degree, the uniaxial compressive strength of the rock will gradually decrease, and the structure will become more and more loose and broken, which has a significant impact on the drilling effect. Unweathered rock, dense structure, high strength, the selection of The conventional high-performance drill bit can meet the drilling needs, such as a tungsten carbide button drill bit, which can efficiently complete the drilling. In breezy rock, the strength is slightly reduced, but the overall structure is still more complete, can properly reduce the performance requirements of the drill bit, choose the hardened button drill bit, ensuring the drilling efficiency at the same time, control costs. Medium weathered rock, rock structure began to crack, strength further declined, need to use a certain impact and cutting dual functions of the bit, such as tungsten carbide cross-cut drill bit, to ensure the smooth drilling. Strongly weathered and fully weathered rocks, soft texture, similar to soil, at this time, clay bit with its special structure, can effectively stir and discharge soft soil, to achieve large bore drilling, and the cost is low, become the first choice for these two degrees of weathered rock drilling.
Summary
In the complex system of rock and soil anchorage engineering, the correct selection of the drill bit of the self-drilling anchor bolt is the cornerstone to ensure the success of the project. From the initial recognition of the unique advantages of self-drilling anchor bolt drill bits to the in-depth understanding of the “expertise” of various types of bits and the selection strategy based on rock characteristics, each step embodies the integration of technology and experience.
Through a comprehensive understanding of this series of related contents of the drill bit, I believe that everyone has a more profound and thorough understanding of the choice of drill bits.
In the future practice of geotechnical anchoring engineering, we hope that we can make full use of this knowledge, and precise selection so that each drill bit of the self-drilling anchor bolt can play the maximum efficiency in the right working conditions, escort the successful implementation of various geotechnical anchoring projects, and promote the steady development of the entire industry in the direction of more efficient and better quality.
