How did the caisson method create a stable base for a lighthouse on soft seabed?

The caisson method creates a stable base for a lighthouse on soft seabed through a systematic process of excavation and reinforcement.

A steel caisson, typically an open-ended cylinder, is positioned on the seabed. To achieve the necessary depth and stability, sand is excavated from within the cylinder, allowing it to sink into the seabed—sometimes as deep as 15 meters (50 feet). As the structure descends, additional sections are added to the top to ensure it remains above the high-water level. Once the desired depth is reached, the interior is pumped dry and filled with concrete. This creates a solid, heavy foundation capable of supporting the lighthouse structure above it.1

This method is particularly effective for offshore construction where traditional foundations are impractical due to soft ground conditions. By transforming a hollow shell into a dense, concrete-filled pillar, engineers provide the structural integrity required to withstand the forces of the open sea.12