Channel Tunnel Thickness: 4.8 Metres Total

The Channel Tunnel (Chunnel) lining thickness is 4.8 metres (15.7 ft) total, comprising:

• Concrete segmental lining: 39.3 cm (15.5 in) thick precast segments, bolted & gasketed.
• Cast-in-place inner lining: ~30–40 cm (varies) for fire protection & finish.
• Rock cover: Average 40–75 m of chalk marl above tunnel crown.

Tunnel Structure

• Three bores: 2 rail tunnels (7.6 m diameter) + 1 service tunnel (4.8 m).
• Length: 50.45 km (31.35 mi), 37.9 km undersea.
• Depth: Max 75 m below seabed, 115 m below sea level.

The 39.3 cm precast segments are the primary structural element—engineered for 120-year design life, water pressure, and train aerodynamic loads.