On the French side, neoprene and grout sealed bolted linings made of cast iron or high-strength reinforced concrete were used; on the English side, the main requirement was for speed so bolting of cast-iron lining segments was only carried out in areas of poor geology. In the UK rail tunnels, eight lining segments plus a key segment were used; in the French side, five segments plus a key.
The French and English sides employed different approaches to lining their railway tunnels. The French utilized neoprene and grout-sealed bolted linings made of cast iron or reinforced concrete, while the English prioritized speed, limiting bolting of cast-iron lining segments only in areas with poor geology. In UK tunnels, eight segments plus a key segment were used; on the French side, five segments plus a key were employed.