In the heart of the Alps, a critical railway tunnel expansion faced some of the most demanding geological conditions in recent European infrastructure history. The project, which aims to increase freight capacity through a 12-kilometer stretch beneath fractured limestone and water-bearing fault zones, required a ground support solution that could combine drilling, injection, and permanent load-bearing capacity in a single, lightweight component. SupAnchor, a global leader in geotechnical reinforcement systems, supplied its SupFRP® GFRP Hollow Injection Bolt—a self drilling anchor bolt engineered for high-pressure grouting and long-term structural integrity.
The tunnel section, located at depths exceeding 800 meters, exhibited squeezing ground behavior, unstable rock masses, and significant water ingress. Traditional rock bolts often failed to achieve adequate bond strength due to poor grout penetration or corrosion in aggressive groundwater. SupAnchor's hollow bar anchor provided a dual-function solution: a drill-and-grout bolt that could be advanced through difficult strata while simultaneously injecting grout under high pressure, ensuring complete encapsulation and immediate load transfer to the surrounding rock mass.
The GFRP Hollow Injection Bolt integrates the functions of a rock bolt and an injection pipe. After drilling and grouting, the bolt remains in the borehole, acting as a permanent reinforcement member together with an end plate and nut. Its hollow core allows for high-pressure grout injection, which fills all fissures and voids, creating a monolithic bond with the ground. The bolt's waved thread structure enhances mechanical interlock with the grout, while its glass fiber reinforced polymer (GFRP) composition provides excellent corrosion resistance and cuttability—critical for later tunnel excavation phases.
For this project, SupAnchor recommended a combination of models based on ground conditions and load requirements. The technical data below highlights three key products deployed:
| Model | Outside Diameter (mm) | Guaranteed Tensile Load (kN) | Pressure Resistance (MPa) | Weight (kg/m) |
|---|---|---|---|---|
| H25/220 | 25 | 220 | 5 | 0.64 |
| H28/320 | 28 | 320 | 5 | 0.88 |
| H32/360 | 32 | 360 | 5 | 1.20 |
The selection of these models addressed specific engineering challenges. The H25/220, with a guaranteed tensile load of 220 kN and a weight of only 0.64 kg/m, offered easy handling in confined tunnel headings. For sections with higher rock stress, the H32/360 provided 360 kN tensile capacity while maintaining a 15 mm internal diameter for efficient grout flow. All models feature a 5 MPa pressure resistance, allowing grout injection pressures sufficient to consolidate fractured ground and seal water paths. The ultimate strain of 2.0% ensures ductility without sudden failure, and the GFRP material's low modulus (45 GPa) better matches rock deformation characteristics compared to steel, reducing stress concentrations at the bolt-grout interface.
The GFRP Hollow Injection Bolt is not limited to tunneling. Its design suits a wide range of geotechnical reinforcement applications, including slope stabilization, TBM face support, forepoling, confined ground conditions, stabilization of soft rock, and permanent installations. In slope stabilization, the hollow bar anchor can be installed quickly on steep terrain due to its low weight, and the high-pressure grouting effectively bonds fractured rock masses, preventing landslides. For TBM face support, the bolt's cuttability allows the TBM cutterhead to pass through without damage, making it ideal for pre-support in soft ground tunnels.
On a global scale, the demand for robust, corrosion-resistant ground anchors is rising. Aging infrastructure, urban underground construction, and mining operations in aggressive environments call for materials that outlast steel. SupAnchor's GFRP bolts offer a service life exceeding 100 years in most soil and rock conditions, significantly reducing long-term maintenance costs. The integration of drilling and grouting into one step also shortens construction cycles, a critical factor in project economics. As infrastructure projects become more complex, the self drilling anchor system is emerging as a preferred method for ground control, and SupAnchor is at the forefront of this evolution.
SupAnchor has established itself as a professional and innovative force in the geotechnical industry. With ISO 9001, ISO 14001, and ISO 45001 certifications, the company adheres to rigorous quality, environmental, and occupational health standards. Its R&D team continuously refines product designs, evidenced by the SupFRP® series' optimization of load capacity to weight ratio. Collaborative partnerships with engineering firms and contractors worldwide have led to successful deployments in major projects across Europe, North America, Asia, and the Middle East.
The company's commitment to solving real-world challenges is reflected in the development of the hollow injection bolt. By listening to field engineers, SupAnchor addressed common pain points—corrosion, heavy weight, poor grout bonding—and delivered a solution that enhances safety and efficiency. As a leading soil nail system manufacturer and ground anchor bolt factory, SupAnchor supplies not only products but also technical support and training, ensuring that every installation meets design specifications. The Alpine tunnel project stands as a testament to the value of professional engineering combined with innovative materials.
In conclusion, the successful application of SupAnchor's GFRP Hollow Injection Bolt in challenging ground conditions underscores the importance of advanced geotechnical reinforcement systems in modern construction. With its high tensile strength, corrosion resistance, and full-grouting capability, this self drilling anchor bolt is poised to become a standard tool for engineers tackling difficult geology. SupAnchor remains dedicated to delivering collaborative, professional, and innovative solutions that keep infrastructure safe, durable, and economical.
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