SOA Category OG4
Everything required for underground engineering works
The OG4 category within the SOA qualification system covers underground civil works – specifically the construction, maintenance, and renovation of road and railway tunnels. As one of the 13 general categories, OG4 plays a strategic role in the transport‑infrastructure sector. OG4 certification attests to a company’s technical and financial capability to build highly complex underground structures, often carried out in challenging geological or environmental conditions. The category includes natural tunnels, cross‑mountain passages, underground corridors, and excavated transit structures in soil or rock, designed for vehicle or rail traffic.
Types of underground works covered by OG4
OG4 is a highly specialized category, required in numerous major infrastructure tenders and reserved for companies with strong technical expertise, dedicated equipment, and integrated competencies. OG4 activities include:
- Road and highway tunnels: Alpine tunnels and major road galleries, including excavation, lining, ventilation, and safety systems.
- Railway tunnels: from high‑speed lines to cross‑border megaprojects, built with strict technical standards and dedicated systems.
- Metro and underground tram systems: excavated beneath densely populated urban areas, with constraints related to groundwater, existing buildings, and traffic.
- Underpasses and minor underground passages: natural‑tunnel works or microtunnelling in confined environments.
- Tunnel auxiliary works: access ramps, retaining structures, technological systems, and railway track installations linked to the main gallery.
Categories that integrate with OG4
Underground works are rarely isolated; major infrastructure projects require the integration of multiple SOA categories:
- OG3 – Roads and railways: OG3 and OG4 are complementary. OG3 covers open‑air sections, viaducts, and embankments; OG4 covers natural tunnels. New highways or railways usually require both.
- OS21 – Special structural works: consolidation of tunnel faces, soil injections, diaphragm walls, and deep foundations. In unstable ground, OG4 and OS21 are almost always paired.
- OS28 / OS30 – Technological systems: ventilation, fire‑safety systems, lighting, electrical supply, and communication systems. In complex tenders, these may be replaced by OG11, which covers all integrated tunnel systems.
- OG5 – Dams and hydraulic tunnels: sometimes overlaps with OG4 for diversion or relief tunnels; however, OG5 remains the leading category for hydraulic works.
- Support categories: OS8 (waterproofing), OS10 (signage), OS11 (structural equipment), OS12‑B (safety barriers), OS19 (telecommunications).
FAQ
SOA Category OG4
OG4 is the category that certifies the ability to build safe, sustainable, and long‑lasting underground infrastructure that connects territories and communities. Obtaining OG4 SOA certification means investing in innovation, technology, and the future of mobility.
To excel in OG4, companies must combine experience, advanced training, and cutting‑edge technology. Qualified enterprises must ensure safety, quality, and strict compliance with timelines – critical elements for competing in public‑works tenders.
Interested in expanding into underground engineering?
Make sure you have the appropriate OG4 qualification and continue investing in people, skills, and innovation.
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