Bridge pylons rest on a foundation that begins deep in the ground below the surface of the water. A system of cables is attached to each side of the bridge and then to the pylons, which transfers the entire weight of the structure through the foundation and into the ground.
When the location of the foundation is determined, steel walls are placed in the water to isolate the area to be excavated. The water is pumped out and excavation begins.
The central portion of the foundation consists of poured concrete reinforced with rebar. Large stones arranged in a trapezoidal configuration surround the concrete from the surface of the water down to the ground below the water's surface.
Building the Pylon
When the foundation is complete, the reinforcing system is framed for the pylon in vertical sections. The concrete is poured for each section as the reinforcing is built for the section above.