In deep foundation pit support projects, faced with the complex geological conditions of loose and collapsible strata, traditional construction methods often face many challenges, such as difficulty in hole formation, low construction efficiency, and high costs. To solve these problems, self-drilling anchor bolts have emerged as an innovative support material and quickly attracted widespread attention in the industry. With its unique design that integrates drilling, grouting, and anchoring, self-drilling anchor bolts effectively overcome construction obstacles in loose and collapse-prone strata and significantly improve construction efficiency and quality. In this paper, we will discuss the advantages of self-drilling anchor bolts in loose and easy-to-collapse hole formations.
The composition of self-drilling anchor bolts
Self-drilling anchor bolt is a new support material that integrates drilling, grouting, and anchoring. It consists of a hollow anchor bar, a drill bit, a coupler, a plate, a nut, and a centralizer. The outer surface of the hollow anchor bar adopts a corrugated thread design, which not only enhances the slag discharge capacity but also effectively prevents hole collapse and drill sticking while improving the gripping force between the rock bolt and the rock and soil mass. In addition, the drill bit part of the self-drilling anchor bolt adopts a one-time simple design, which can complete the drilling task by itself under the driving of the drilling rig, greatly simplifying the construction process.
Features of self-drilling anchor bolts
Compared with ordinary mortar anchor rods, hollow grouting anchors do not need to be pulled out and are suitable for various strata, avoiding the need for wall grouting or pipe drilling in similar strata and the collapse and rework of the hole after pulling out the drill rod after drilling, slow progress or rework, etc. During construction, the hollow grouting anchor does not need casing to protect the wall, and drilling and grouting make it easy to form anchor holes and ensure the anchoring and grouting effect. Compared with ordinary mortar anchor rods, hollow grouting anchors improve the construction quality under loose and easy-to-collapse strata.
Self-drilling anchor bolts have construction advantages that ordinary rock bolts do not have in terms of performance. Although the cost and price of self-drilling anchor bolts are high in terms of drilling materials alone, under the same construction conditions, ordinary rock bolts should circulate wall grouting or pipe drilling, while self-drilling anchor bolts can overcome these problems. The construction is simple and fast. From the perspective of comprehensive construction costs, self-drilling anchor bolts are more economical than ordinary rock bolts.
Construction process
The construction process of self-drilling anchor bolts is relatively simple, mainly including construction preparation, drilling rig debugging, measuring and placing points, connecting grouting pipes, preparing slurry, installing rock bolts, synchronous drilling and grouting, etc. During the drilling process, the grouting is synchronized, which effectively ensures the formation of anchor holes and the anchoring effect. Compared with traditional methods, self-drilling anchor bolts do not require casing wall protection, reduce the risk of hole collapse, and improve construction efficiency and safety.
Engineering application cases
Take a tourist block development and construction project as an example. The depth of the foundation pit of the project is about 7.3 to 7.8 meters, and the circumference is about 1,200 meters. The geological conditions are complex, including mixed-fill soil, silt, fine sand, gravel, and other strata. Under such construction conditions, the designer adopted self-drilling anchor bolts as temporary support structures, which achieved remarkable results.
In practical applications, self-drilling anchor bolts have shown excellent support effects. Through the pull-out test, the anchoring force of the anchor fully meets the design requirements. At the same time, on-site monitoring results show that the supporting structure is stable and reliable, effectively ensuring the safe progress of foundation pit construction. Compared with traditional construction methods, self-drilling anchor bolts show clear advantages in cost and time. Project statistics show that the average drilling speed of self-drilling anchor bolts reaches 1m/min, and the average drilling depth per shift can reach 200m. Compared with casing drilling, the construction efficiency is significantly improved, and the construction cost is the same or even slightly lower.
Conclusion
The efficient application of self-drilling anchor bolts in deep foundation pit support in loose and prone-to-collapse strata fully demonstrates its unique technical advantages and significant economic benefits. Through integrated construction, wide applicability, solving construction problems, and improving anchoring effects, self-drilling anchor bolts simplify the construction process, improve construction efficiency, and significantly enhance the stability and safety of the supporting structure. With the increasing number of foundation pit projects and the increasingly complex geological conditions, the application prospects of self-drilling anchor bolts will be broader. We believe that self-drilling anchor bolts will continue to play an essential role in future deep foundation pit support projects, making more contributions to guaranteeing project quality and safety, reducing construction costs, and shortening the construction period. At the same time, with the continuous advancement and innovation of technology, the performance of self-drilling anchor bolts will be further improved, bringing more surprises and breakthroughs for civil engineering.
