Existing comment:
1870
The Bridge Foundations
The majestic towers of the bridge rest on wooden foundations called pneumatic caissons. Each caisson is a giant bottomless chamber which was built on land and slowly sunk to the river bed exactly where the tower was to rise. Inside the chamber, workers excavated debris until firm ground to support the weight of the tower was reached. The caisson was then filled with concrete.
1870
The Tower's Begun
The stone blocks for the towers were lifted into place by boom derricks and a system of steam pulleys. The weight of the first stone course for the tower caused the caisson to settle to the river bed; the excavation began. |