As urbanization intensifies and aging infrastructure demands renewal, tunneling and deep excavation projects are increasingly pushing the boundaries of geotechnical engineering. In a landmark metro expansion project in Copenhagen, Denmark—the Cityringen line—contractors faced a daunting mix of water-bearing sands, soft clays, and glacial till. Traditional drilling methods with casing required extensive time and posed risks of ground loss and settlement in the historic city center. To overcome these challenges, the project team turned to SupAnchor's R Thread Self-Drilling Hollow Anchor, a geotechnical reinforcement system that has become a mainstay in over 39 million meters of global ground engineering.
The R thread anchor embodies the "3-in-1 principle": a single ribbed hollow steel bar serves simultaneously as a sacrificial drill rod, a grout injection tube, and a permanent reinforcing tendon. This innovation eliminates the need for temporary casing and separate grouting steps, slashing installation time and costs by up to 50% compared to conventional methods. On the Cityringen project, crews achieved an average installation rate of 80 anchors per day, maintaining borehole stability in loose, water-charged sands that would have collapsed without immediate support.
The anchor bar features a continuous ISO 10208 R thread profile, available in both left-hand and right-hand configurations. This standardization ensures quick, precise coupling with nuts, extension couplers, and bearing plates, while the full-length thread guarantees a robust mechanical bond with the cement grout. The thread form is optimized to transmit percussive drilling energy efficiently and to provide excellent load transfer once grouted. According to lead geotechnical engineer Lars Petersen, "The R thread system allowed us to install over 10,000 hollow bar anchors in record time while maintaining strict tolerance for ground movement. The 3-in-1 capability was a game-changer for our schedule and safety."
With design lives often exceeding 100 years in infrastructure projects, corrosion protection is a critical concern. SupAnchor addresses this with three distinct options. Hot-dip galvanizing (HDG) offers a zinc coating that provides basic protection in dry or mildly moist environments. For moderately aggressive conditions—such as industrial areas, damp soils, or groundwater with elevated chloride content—the advanced SupCoating system combines an HDG layer with a resilient epoxy outer coating. This dual barrier prevents underfilm corrosion and seals micro-cracks that might compromise a single coating. In the most extreme exposures, including coastal marine environments, salt-laden soils, and chemical plants, stainless steel anchors deliver ultimate resistance against pitting and crevice corrosion.
On the Copenhagen metro, sections with saline groundwater intrusion necessitated the use of SupCoated R32 anchors. Independent testing confirmed a corrosion protection life exceeding 120 years in these conditions, assuring the project owner of minimal long-term maintenance. "Knowing we could tailor the protection level to each segment gave us confidence that the investment would stand the test of time," Petersen added.
The R thread family is engineered to cover a broad spectrum of load demands, from light soil nailing to heavy-duty tieback walls. The following table highlights some of the most commonly used models, showcasing their robust mechanical properties:
| Model | OD (mm) | ID (mm) | Ult. Load (kN) | Yield Load (kN) | Weight (kg/m) |
|---|---|---|---|---|---|
| R25N/12 | 25 | 12 | ≥200 | ≥150 | 2.30 |
| R32L/22 | 32 | 22 | ≥250 | ≥200 | 2.75 |
| R32N/20 | 32 | 20 | ≥280 | ≥230 | 2.85 |
| R32N/18.5 | 32 | 18.5 | ≥280 | ≥230 | 3.30 |
| R32S/17 | 32 | 17 | ≥360 | ≥280 | 3.50 |
Beyond these, the R thread lineup extends to larger diameters and higher strengths. Models like R38N/21, R38/550, and R38/600 offer ultimate loads up to 600 kN, while the R51 series—including R51L/36, R51N/33, R51N/30, and the mighty R51/1000 and R51/1200—can sustain working loads exceeding 1,200 kN, making them suitable for permanent anchorages in dam stabilization and high-rise foundation bracing. All bars are manufactured from high-quality carbon steel per EN10083-3 or EN10025, with elongation values A100mm ≥6% and Agt ≥5%, ensuring ductile behavior under overload conditions.
On site, the self drilling anchor bolt is driven using a standard rotary-percussive drill rig. Flush medium (typically air, water, or foam) exits through the drill bit ports, carrying cuttings up the annulus and out the collar. Once the design depth is achieved, a cementitious grout is pumped through the bar's hollow core, flowing from the bit end and backfilling the borehole while permeating the surrounding ground. A bearing plate and torque nut are then tightened, applying immediate preload that actively compresses the ground arch. This rapid installation cycle reduces worker exposure to unsupported ground and allows follow-on works—such as shotcrete application or tunnel excavation—to commence without delay.
The R thread hollow bar anchor finds its most critical use in tunneling, where it provides face stabilization in soft ground, forepoling umbrellas over crown headings, and radial bolting in rock tunnels. In slope engineering, it reinforces unstable hillsides, stabilizes landslide-prone cuts, and supports retaining walls under surcharge loads. Urban construction benefits from its vibration-free installation and minimal spoil generation, which reduce traffic disruption and environmental impact.
In alpine regions, the anchor excels in fractured, blocky rock masses where conventional rock bolts may fail due to lack of bond. The injection grout fills joints and fissures, transforming weak rock into a coherent reinforced arch. For temporary works like braced excavations or emergency slope repairs after heavy rainfall, the system's rapid installation can make the difference between a controlled worksite and a catastrophic failure. As a leading soil nail system manufacturer, SupAnchor provides a complete package: hollow bars, couplers, nuts, plates, centralizers, and drill bits—all manufactured under ISO 9001 quality control to ensure perfect compatibility and reliable performance.
The global push for sustainable and resilient infrastructure demands construction methods that conserve resources and speed delivery. The self drilling anchor system significantly reduces the carbon footprint of anchoring works by eliminating temporary steel casings and cutting drilling time. Its immediate load-bearing capability often allows the elimination of heavy temporary support structures, further reducing material consumption. On the Cityringen project, an independent sustainability audit calculated a 25% reduction in CO₂ emissions per linear meter of installed anchorage compared to traditional cased methods.
With over 39 million meters installed in more than 50 countries, SupAnchor's track record spans iconic projects from the Gotthard Base Tunnel in Switzerland to the Riyadh Metro in Saudi Arabia. The R thread's ISO 10208 compliance ensures it integrates seamlessly into designs governed by Eurocode 7, ACI 318, or BS 8081, giving engineers worldwide the confidence to specify it without lengthy product approval procedures. In North America, where the Infrastructure Investment and Jobs Act is driving a surge in transportation and water projects, the demand from every ground anchor bolt factory has spiked; SupAnchor's production facilities have responded with expanded capacity and just-in-time logistics.
SupAnchor's ethos—Professional, Innovative, Collaborative—is embedded in its R&D culture. The company maintains a full-scale testing laboratory where anchors are subjected to static and dynamic pull-out tests, fatigue loading, and accelerated corrosion trials. Data from thousands of pull-out tests on R32 series anchors confirm bond strengths exceeding those predicted by current design methods, enabling engineers to optimize anchor spacings and lengths.
The recent development of the R32/320 grade, with an ultimate load of 320 kN, fills a performance gap between standard and high-strength options, giving designers greater flexibility. Collaborating with tunneling contractors, SupAnchor has also introduced specialized nut geometries that facilitate robotic screwing for fully automated jumbo installations—a step toward Industry 4.0 in underground construction.
"Our customers aren't just buying steel; they're buying reliability and engineering support," said Klaus Meier, SupAnchor's European Technical Director. "From the first site visit to the final pull-out test, we work shoulder to shoulder with the project team. That's what sets us apart."
As climate change drives more extreme weather and sea-level rise, the need for corrosion-proof, durable ground anchors will only intensify. SupAnchor's R thread self-drilling hollow anchor, with its proven efficiency and adaptability, is well-positioned to anchor the infrastructure of tomorrow. Whether it's securing a high-speed rail tunnel through the Alps or stabilizing a coastal revetment, this drill-and-grout bolt delivers on the promise of safe, fast, and sustainable geotechnical reinforcement.
SupAnchor’s self drilling anchor system provides critical ground stabilization for a major European tunnel project, demonstrating advanced geotechnical reinforcement technology.
SupAnchor's R thread self-drilling hollow anchor combines drilling, grouting, and reinforcing in one step. With ISO-standard threads and anti-corrosion options, it boosts safety and efficiency in tunneling and ground engineering.
The Brenner Base Tunnel project in the Alps employed SupAnchor's self drilling anchor bolts to overcome fractured rock and water inflows, demonstrating the value of advanced geotechnical reinforcement systems.
SupAnchor's T thread self-drilling hollow anchor system integrates drilling, grouting, and reinforcement in one step, delivering high load capacity and corrosion resistance for tunnels, slopes, and foundations worldwide.
A major infrastructure project in the Alps successfully utilized SupAnchor's self-drilling anchor system to overcome fractured rock conditions, enhancing geotechnical safety and project efficiency.
