Tunnels
What it is
Underground passages for roads, rail, water or services.
How it works
The ground around the opening is supported until a permanent lining takes over, while drainage keeps water out.
Diagram: Indiacon original, not to scale.
Main components
Portals, excavation, primary support (bolts, shotcrete), lining, waterproofing, ventilation, escape routes.
Key codes
IS 15026, IRC SP 91. Cited by number only; get the text from BIS or the issuing body.
Notable projects
Atal Tunnel, Gotthard Base Tunnel (Switzerland), Channel Tunnel (UK–France), Fehmarnbelt (Denmark–Germany).