Engineering Wonders of the World
Volume III

HARBOUR CONSTRUCTION. 79 PLAN OF NEW ADMIRALTY HARBOUR, DOVER. The works marked in solid black have recently been completed bv Messrs. S. Pearson and Son. foot breakwater at the east end ; (4) building an island breakwater on the south, between the heads of the two arms. The form of structure adopted for the breakwaters was a wall between 50 and 60 feet wide at the base, built on the sea bottom, and tapering upwards gradually to a height varying between 80 and 90 feet. For all the walls large concrete blocks, weighing up to 42| tons, were used, those set on the sea faces being covered with granite ashlar built up inside the moulds before the concrete was poured in. The contractors began operations on the Admiralty Pier extension, and cutting away the chalk cliff along the easterly half of the strip of shore included in the harbour. The chalk, detached by gangs of men roped to- gether for safety, was dumped in the sea behind a retaining wall of 3-ton blocks. Eventually ample room was secured for block- making yards, workshops, and storehouses. As a preliminary to construction w.ork, the shore end of the great gantries to carry the 100-ton Goliath cranes had to be built by , driving in great iron-shod The Goliath .. ,• . ° Gantries. Plles’ 100 feet long and from 18 to 20 inches square, in groups of six, three on each side of the line of the future blockwork, and by connecting the groups with horizontal girders and bracings. The girders were covered with a heavy timber flooring as a base for the Goliath and block- truck tracks. Oregon pine piles were used in the first instance, but replaced subsequently by sticks of Tasmanian blue gum, which, being heavier than water, does not float when detached, to the danger of shipping, and is immune from the ravages of the sea-worm. When a gantry had been advanced suffi- ciently a Goliath was erected on it, to work the grabs and breakers used for levelling roughly the sea bottom. Behind this crane followed a second for the diving-bells, under cover of which divers levelled the surface accurately. A succeeding crane did the under- water block laying, the crane-men working in accordance with signals sent up by divers, and a fourth placed the above-water courses. This system made for general rapidity of progress, as all the stages of construction proceeded simultaneously when weather and tide permitted. It is interesting to note that the Admiralty Pier extension was built at more than six times the speed of the old pier —600 feet in a year compared with about 90 feet. To save time, the contractors wished to build the island breakwater independently of shore connections ; but, owing to diffi- culties in securing a starting-point in the open sea, it was found necessary to prolong the gantries of the east arm and bring up the cranes and material over that arm, closing tem- porarily the south-east entrance to the harbour. About 64,000 blocks, weighing together 1,920,000 tons, have been used in forming the breakwater walls. To get the grand total of about 3,000,000 tons we add the blocks for the retaining wall of the reclamation and the horizontal apron blocks laid on the sea- ward side of the breakwaters. The excellent views which, by the courtesy of Messrs. S. Pearson and Son, we reproduce, will give the reader a better idea of the constructional operations than could be conveyed by words.