Across Europe's mountainous regions, tunnel construction has long been plagued by unconsolidated ground and time-consuming drilling with casing systems. On a recent high-speed rail tunnel project in the Alps, contractors encountered mixed ground comprising sandy gravel, silty clay, and weathered rock. Traditional drilling methods required installing a temporary casing to prevent borehole collapse, followed by separate grouting and anchor installation—a multi-step process that slowed production and increased labor costs. To overcome these challenges, the project turned to SupAnchor's R Thread Self-Drilling Hollow Anchor, a drill-and-grout bolt that streamlines the entire anchoring sequence.
Developed in response to the tunneling and ground engineering industries' demand for safer and faster production, the R Thread self-drilling hollow anchor from SupAnchor tackles one of the most persistent challenges in underground construction: how to install a reliable anchor in unstable ground without the time-consuming use of casing systems. In unconsolidated or cohesive soil, conventional drill-and-place anchors often require a temporary casing to keep the borehole open until the anchor and grout are installed. This multi-step process is not only slow but also increases the risk of collapse and grout loss. The R Thread system eliminates these problems by allowing a single hollow bar to drill, grout, and reinforce in one continuous operation.
The system is built around a ribbed hollow steel bar that serves three functions simultaneously: a sacrificial drill rod, an injection tube, and a reinforcing bar. This 3-in-1 principle is the foundation of the self drilling anchor system's efficiency. The bar's ISO 10208-compliant thread profile allows for rapid connection and disconnection of drilling bits, couplers, and nuts, minimizing downtime and simplifying logistics on site.
At the core of the R Thread system is a range of hollow bar anchors designed to meet diverse load and ground conditions. The table below presents key technical parameters for three representative models from the series.
| Model | Outside Diameter (mm) | Internal Diameter (mm) | Ultimate Load (kN) | Yield Load (kN) | Weight (kg/m) |
|---|---|---|---|---|---|
| R25N/12 | 25 | 12 | ≥200 | ≥150 | 2.30 |
| R32N/20 | 32 | 20 | ≥280 | ≥230 | 2.85 |
| R32S/17 | 32 | 17 | ≥360 | ≥280 | 3.50 |
These models illustrate the range of load capacities available. The R25N/12, with an ultimate load of at least 200 kN, is lightweight and ideally suited for forepoling and face stabilization in small- to medium-diameter tunnels. The R32N/20 offers a higher ultimate load of 280 kN while maintaining a relatively modest weight of 2.85 kg/m, making it a versatile choice for ground anchors in slope stabilization. For more demanding retaining wall support or deep excavation projects, the R32S/17 delivers an ultimate load of up to 360 kN thanks to its thicker steel cross-section (440 mm²), providing a robust geotechnical reinforcement system.
All models in the R Thread series are available in lengths from 2 to 8 meters, with left-hand or right-hand thread options. Standard accessories include anchor nuts, couplers, and plates, all designed to work seamlessly with common drilling equipment. The hollow core diameter is optimized for efficient grout flow, ensuring that the injected cementitious grout fills the annular space and penetrates the surrounding soil, forming a strong mechanical and chemical bond.
Because tunnel and ground anchors are exposed to moisture, aggressive soils, and sometimes chemical contaminants, ensuring long-term structural integrity is critical. SupAnchor offers three anti-corrosion protection levels for the R Thread self drilling anchor bolt product line:
On the Alpine tunnel project, the contractor selected SupCoating for the majority of the anchors due to the presence of groundwater with moderate sulfate content, while stainless steel bars were used in the portal areas exposed to de-icing salts. This strategic use of anti-corrosion options extended the design life of the support system and reduced long-term maintenance costs.
The R Thread self-drilling hollow anchor is engineered for unconsolidated or cohesive soil conditions, making it a versatile tool across multiple geotechnical disciplines. Its primary applications include:
Because the system combines drilling and grouting in a single pass, it significantly reduces the number of equipment setups and manual interventions. This not only accelerates construction schedules but also minimizes the risk of borehole collapse, a common failure mode when drilling through cohesionless soils. Furthermore, the grout injected through the hollow core fills voids and improves the ground's mechanical properties, enhancing overall stability.
As global infrastructure investment accelerates—especially in rail, highway, and underground space development—contractors are increasingly seeking systems that reduce project risk and labor costs. The self drilling anchor system from SupAnchor addresses both needs by shortening installation cycles and improving safety. According to industry analyses, drill-and-grout bolts can cut anchor installation time by up to 40% compared to conventional casing methods. In tunneling, where time is literally money due to high overhead and equipment costs, such efficiency gains have a direct impact on the bottom line.
Moreover, the ability to inject grout through the hollow bar ensures a strong bond with the ground, enhancing load transfer and improving overall stability. This characteristic is particularly valuable for projects in urban environments where surface settlement must be strictly controlled. By providing immediate support and allowing for pressure grouting, the R Thread system helps engineers meet stringent deformation criteria.
SupAnchor's R Thread series is manufactured under strict quality control in accordance with ISO 10208 and ISO 1720 standards. The company reports that over 39,000,000 meters of self-drilling anchor bars have been safely applied worldwide—a figure that underscores the system's field-proven reliability. As a leading soil nail system manufacturer and ground anchor bolt factory, SupAnchor continues to invest in R&D to develop products that meet the evolving demands of modern geotechnical engineering.
The R Thread product line is backed by a global distribution network and technical support team, ensuring that engineering consultants and contractors can access the right anchor specification for their project. With options for left- or right-hand threads, multiple lengths from 2 to 8 meters, and a range of steel grades, the system offers exceptional flexibility. Additional models such as R38N/21, R51L/36, and R51/660 expand the selection to cover higher load capacities and larger diameters for heavy civil applications.
As underground construction pushes into more challenging ground, the R Thread self-drilling hollow anchor stands out as a reliable, efficient, and adaptable drill-and-grout bolt. Its combination of high tensile strength, corrosion protection options, and one-pass installation makes it an essential tool for modern tunneling and ground engineering projects. For engineers and contractors seeking a proven geotechnical reinforcement system, SupAnchor's R Thread series delivers the performance and versatility needed to keep projects on schedule and within budget.
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