Norway is drilling the world's longest and deepest undersea road tunnel through fault zones and rock that keeps letting seawater in

Norway is drilling the Rogfast tunnel, the world's longest and deepest undersea road tunnel, stretching nearly 27 km and reaching almost 400 m below sea level.

The tunnel passes through fault zones where crushed and fractured rock presents unpredictable geological conditions.

Crews have encountered extensive saltwater leaks at roughly 300 m below sea level, requiring specialized grouting and sealing methods.

Norwegian regulations require at least 50 m of solid rock between the tunnel and the sea above for safety.