As urban infrastructure expands, tunneling through soft, water-bearing ground presents formidable geotechnical challenges. Recently, a major cross-city metro tunnel project in Southeast Asia faced severe ground instability in loose silty sand and weathered rock. Conventional drilling with casing proved too slow and risked collapse. The project needed an anchoring solution that could drill, inject grout, and reinforce simultaneously—without removing the drill string. The answer came from SupAnchor’s T thread self-drilling hollow anchor system, a hollow bar anchor that merges drilling rod, injection tube, and reinforcing bar into a single continuous element. Within weeks, the system stabilized the tunnel face, accelerated excavation cycles, and set a new benchmark for construction safety in difficult ground.
The T thread self-drilling hollow anchor follows the proven “3-in-1 principle.” Its ribbed hollow steel bar acts as a sacrificial drill bit, a grout injection tube, and a permanent reinforcement bar. Drilling and grouting happen in a single pass, eliminating separate casing systems and slashing installation time—critical in unconsolidated or cohesive soils where traditional methods often fail. On the tunnel project, crews used rotary percussive drilling with left-hand T thread bars, achieving rapid penetration without blockages. After reaching design depth, cement grout was pumped through the hollow core under low pressure, filling the annulus and permeating the surrounding ground, creating a continuous geotechnical reinforcement system.
The bar’s rib geometry was engineered for superior bond strength. The relative rib area (fR) ranges from 0.21 to 0.33—close to the theoretical optimum—while the 45° rib angle reduces splitting forces on the host material. At maximum load, crack widths stay below 0.1 mm, ensuring durable crack control even under high stress. This design maximizes load transfer from the steel to the grout, turning the assembly into a high‑capacity soil nail system. To illustrate the system’s capabilities, key technical data for three commonly used models are presented below:
| Model | Outer Dia. (mm) | Inner Dia. (mm) | Cross‑section (mm²) | Ultimate Load (kN) | Yield Load (kN) | Weight (kg/m) |
|---|---|---|---|---|---|---|
| T30/16 | 30 | 16 | 343 | ≥220 | ≥180 | 2.70 |
| T30/11 | 30 | 11 | 406 | ≥260 | — | ~3.3 |
| T40/16 | 40 | 16 | 913 | ≥660 | ≥525 | 7.17 |
All models feature the T International Standard thread (left‑ or right‑hand), allowing quick on‑site coupling with standard percussion equipment. The standardized thread also guarantees compatibility with nuts, couplers, and plates, streamlining logistics and assembly. For the tunnel project, the T30 series provided immediate face support; the T40/16 anchors were later employed in critical arch zones where higher yield loads were needed. The integrated construction method cut the drill‑and‑grout cycle by more than 40% compared to conventional casing methods, proving the system’s value as a true drill-and-grout bolt.
Groundwater chemistry and exposure conditions dictate the service life of any anchoring system. SupAnchor’s T thread hollow bar anchors come with three corrosion‑protection levels, tailored to the site’s aggressiveness:
This layered anti‑corrosion philosophy allows engineers to optimize cost and durability, reinforcing SupAnchor’s reputation as a forward‑thinking ground anchor bolt factory that supplies complete, certified systems rather than isolated components.
Beyond the metro tunnel, the T thread series is proving its versatility across a wide spectrum of geotechnical works:
The range extends well beyond the models detailed above. Larger self drilling anchor bolts like T76/1400, T103/3034, and T114/3450 cater to heavy‑duty tunnel support and major slope stabilization, delivering ultimate capacities exceeding 1400 kN. All maintain the same T thread standard and optimized rib profile, ensuring seamless integration into existing workflows. With global infrastructure investment surging—the G20’s Global Infrastructure Hub estimates USD 15 trillion will be spent on transport infrastructure by 2040—reliable, efficient anchoring technologies like this self drilling anchor system are in growing demand.
SupAnchor, recognized as the No. 1 manufacturer and exporter of self‑drilling anchors in Asia, combines rigorous R&D with ISO‑certified production to deliver anchors that meet international standards. The T thread system is manufactured under ISO 9001 and ISO 14001, with full material traceability. The company’s collaborative approach—working with contractors and consultants from design concept through installation support—has made it a trusted partner on projects from high‑speed rail in Europe to hydro‑power tunnels in Latin America. By continuously refining rib geometry, anti‑corrosion coatings, and thread standardization, SupAnchor translates field feedback into engineering innovation, reinforcing structures and safeguarding lives around the world.
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