Thompson Graving Dock

office]] In October 1903, construction of Thompson Graving Dock was started. It was dug next to Alexandra Dock. The design was made in-house by the Belfast Harbour Commission. The work was carried out by contractors Walter Scott & Middleton. The excavation of the new dry dock alongside Alexandra Dry Dock, caused two accidents. During construction, the action of the pumps at the new dock carried away a substratum of fine sand. It caused two subsidences of Alexandra Dock's walls. The first happened in October 1905 and a second more serious one happened in April 1906. The damage was so serious that Alexandra Dry Dock was only repaired by the end 1907. This made that several large ocean-going…

Thompson Graving Dock resembles a big rectangular box dug out of the earth. Even so, it has sides and a floor covered in granite. The side walls are 18 ft thick. The floor is 17 ft thick. Like all the earlier docks in Belfast, it was made in stepped masonry. Stepped masonry is a technique to build a solid foundation in brick. Foundation is crucial to prevent a dry dock's floor from collapsing under the weight of a docked vessel. The side walls of the dock are rectangular, except for a series of steps near the top. The dry dock was closed by a caisson gate. This is a large floating steel box. It can be flooded to seat it in the opening of the dock and close it. If enough water is pumped out…