A Treatise On The Principles And Practice Of Harbour Engineering

BREAKWATER DESIGN. 147 contain 6,301,407 short tons1 of stone. To September 1904, 1,690,178 tons had been deposited. Piers at Tynemouth. —The Tyne piers commenced in 1855 for the purpose of sheltering the mouth of the River Tyne, constitute an example of the composite type in which the wall predominates. The rubble mound, which acts as a foundation to the wall (see fig. 122), has since been discarded in connection with the reconstruction of a portion of the north pier, due to a breach in it, 100 yards wide, made by a storm in 1897. The mural portion of the original structure consisted of two longitudinal masonry walls connected at frequent intervals by cross walls, the cavities or pockets between being filled near the shoreward end with quarry débris, and, further seaward, with mass concrète. “ The depth of the foundations of the superstructure varies from low- water level at the shoreward end to 27 feet lower at the pierhead. This Shale' Shala Typical Section of Old Work. Typical Section of New Work. Fie. 122. —River Tyne Breakwater. depth of foundation at the pierhead is much greater than was originally contemplated, it having been discovered, while the work was in progress, that wave action took place at much greater depths than had previously been supposed. The depth of the foundations would probably have been carried still lower had it not been that the rubble mound was deposited very much in advance of the superstructure, in order to ensure its being sufficiently consolidated before being built upon. The whole work seems to have stood well until the winter 1893-94, after which it was found that some of the foreshore blocks had been moved and the foundations of a short length of pier exposed.” After the more serious breach of 1897, the question of reconstruction was considered, and, upon careful deliberation, the Tyne Commissioners decided to form a length of new work within the line of the old work, as shown in fig. 123. “ In the new work the rubble mound is being dispensed with, and the foundations are being taken down to a hard shale, the depth averaging about 1 Tons of 2000 Ibs.