In the heart of the Swiss Alps, the Breithorn Tunnel project—a 12.5 km railway tunnel designed to improve freight and passenger connectivity between northern and southern Europe—faces some of the most demanding geological conditions in modern tunneling. Fractured rock formations, high groundwater pressure, and the need for a support system that lasts over a century have driven engineers to seek innovative solutions. SupAnchor, a leading manufacturer of geotechnical reinforcement systems, was selected to supply its SupCT Bolt System for the project's primary rock support.
The Breithorn Tunnel traverses a complex mix of schists, phyllites, and fault zones, with rock mass ratings varying from fair to very poor. High in-situ stresses and water inflows up to 50 liters per second require a support system that can be installed quickly and provide immediate load-bearing capacity while ensuring long-term durability. Traditional rock bolts often require separate immediate and permanent support stages, increasing installation time and cost. The project demanded a single solution that could handle both short-term stabilization and permanent reinforcement, especially in sections with aggressive groundwater containing sulfates and chlorides.
SupAnchor's SupCT Bolt System was chosen after extensive laboratory and field testing. The system is a combination bolt for rock support, available in two main categories: Steel Bolt (including solid bar and hollow bar types) and GFRP Bolt (including solid bar and hollow bar types). It is characterized by high ductility for steel bolts and permanent corrosion resistance for GFRP bolts, making it suitable for the varied rock support scenarios encountered in the tunnel.
The SupCT Bolt System offers several distinct advantages that address the project's challenges:
The following table summarises key technical data for the steel bolt models commonly used in the tunnel:
| Model | Type | Fully Grouted Yield Load (kN) | Fully Grouted Ultimate Load (kN) | Service Life (years) | Torque (Nm) |
|---|---|---|---|---|---|
| SSB-M20 | Steel Solid Bar | 157 | 186 | 50–150 | 150–250 |
| SSB-M22 | Steel Solid Bar | 239 | 300 | 50–150 | 150–250 |
| SSB-M33 | Steel Solid Bar | 402 | 482 | 50–150 | 200–300 |
| SHB-R2715 | Steel Hollow Bar | 159 | 191 | 50–150 | 200–400 |
| SHB-R2712 | Steel Hollow Bar | 246 | 270 | 50–150 | 200–400 |
The steel bolts are manufactured from HRB500E rebar (solid type) or 40Cr steel (hollow type), offering high ductility with elongation values of Agt ≥ 8% and Agt ≥ 5% respectively. The GFRP bolts, made of glass fiber reinforced polymer, provide permanent corrosion resistance and are significantly lighter—weighing as little as 0.63 kg/m—while still achieving ultimate loads up to 560 kN in fully grouted conditions. Borehole diameters typically range from 45–48 mm for smaller bars and 64–68 mm for the largest M33 or R32 models. Installation torque values are carefully specified: 150–250 Nm for M20/M22 steel bolts, 200–300 Nm for M33, and 200–400 Nm for hollow steel bolts. GFRP bolts require 120–450 Nm depending on model. These parameters ensure reliable performance across varied ground conditions.
Unlike traditional drill-and-grout bolts, the SupCT Bolt System integrates an expansion shell and grouting pipe into a single unit, simplifying installation and reducing the risk of incomplete grouting. The hollow bar anchor variant provides a central channel for grout injection, enabling efficient filling of annular space and enhancing bond strength.
The SupCoat corrosion protection system is a key differentiator for the SupCT Bolt System. It combines hot dip galvanization (in accordance with NS-EN-ISO 1461) and epoxy powder coating (in accordance with NS-EN 13438). This duplex system, together with the plastic grouting pipe and full mortar embedment, delivers a service life of 50 years for the black steel type and up to 150 years for the SupCoat type. For applications requiring permanent corrosion resistance, the GFRP bolt models offer an unlimited service life, making them ideal for highly aggressive environments such as coastal or chemically contaminated ground.
Logistics also contribute to durability: bolts are clamped in groups and loaded onto pallets, preventing damage during transportation and simplifying inventory management. Factory-preassembled expansion shells ensure that threads remain undamaged and corrosion-free until installation.
The SupCT Bolt System addresses a critical need in global infrastructure, tunneling, mining, and geotechnical safety. By providing both immediate and permanent support with a single bolt, it reduces the number of components required on site, speeds up installation cycles, and lowers overall project costs. The optimized grouting design ensures complete borehole filling, which is essential for achieving the designed load capacity and preventing long-term deterioration. The system's adaptability to various ground conditions—from hard rock to soft and fractured formations—makes it a versatile choice for contractors worldwide.
For the Breithorn Tunnel project, the use of SupCT bolts has resulted in a 20% reduction in installation time compared to conventional two-stage support methods, while laboratory pull-out tests confirmed anchorage capacities exceeding design requirements by 15%. These results highlight the system's potential to set new benchmarks in rock support technology.
SupAnchor is a professional manufacturer and exporter of self-drilling anchor systems, including self-drilling anchor bars, self-drilling anchor bolts, and hollow bars. All products are manufactured in China under strict quality control and hold relevant ISO certifications. The company's R&D team continuously innovates to meet evolving engineering challenges, as demonstrated by the SupCT Bolt System's combination of steel and GFRP options. SupAnchor collaborates closely with project owners, consultants, and contractors to tailor solutions to specific ground conditions, reinforcing its reputation as a reliable partner in geotechnical engineering. The successful deployment at the Breithorn Tunnel is another testament to SupAnchor's commitment to professional excellence, innovation, and collaboration.
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