Engineering Wonders of the World
Volume I

THE ROTHERHITHE TUNNEL. 51 ROTHERHITHE TUNNEL PLAN AND SECTIONAL ELEVATION OF THE TUNNEL. of 180 yards to the first shaft (No. 1), built on the “ cut-and-cover ” system, to be described later. After passing this shaft, the roadway, still descending, enters the tunnel proper, which was driven by the shield method and lined with cast iron. About 300 yards farther on, No. 2 shaft is reached, the deepest point of the tunnel, where are situated the pumps for dealing with the small amount of water due to leakage, that used for washing the roadway, and the rain-water from the open approaches. Passing through this shaft, we reach the “ subaqueous ” portion of the tunnel. This is nearly level, but rises slightly to give a fall to the drainage. (See plan.) A length of 515 yards separates Shafts Nos. 2 and 3. Practically all of this length lies under the river, which is crossed obliquely in order to avoid the docks situated on each side. Near No. 3 shaft the ascent begins, the first section to No. 4 shaft being 390 yards long, and curved for most of the distance. North of No. 4 shaft there is another length of “ cut-and-cover,” 200 yards long, followed by the open approach, which is 360 yards in length, measured up to Commercial Road. The open approaches consist of gradually deepening trenches or cuttings in the ground. The earth at the sides is supported by retain- ing walls of concrete, and the bottom, or invert, also con- Open sists of concrete. The invert Approaches, is required to withstand the upward pressure of the water in the ground. On both sides of the river, just below the sur- face soil, is the gravel known as “ Thames ballast,” saturated with water, which, in the absence of a strong floor, would be forced up between the side walls. The open approach on the south side is of special interest, owing to the fact that, as before mentioned, it passes over the East DANMARKS TEKNISKE BIBLIOTEK