Engineering Wonders of the World
Volume III

74 ENGINEERING WONDERS OF THE WORLD. land the largest concrete blocks that have ever been transported in their complete con- dition. Each block measured 27 by 211 by 12 feet, contained nearly 5,000 cubic feet of concrete, and weighed 350 tons. After being allowed to dry for ten weeks a block was lifted by a shears on a floating pontoon, carried to its site, and lowered on to the foreshore, where, until now, it has helped to protect the foreshore and sea wall most effectively. For a really extraordinary example of the forces with which the engineer has to contend we may cite What the Waves did at Wick. the dislocation of the super- structure of Wick Harbour. In 1871 the head of the super- structure was formed as fol- lows : on the levelled top of the rubble mound a single course of 100-ton concrete blocks ; then two courses of 80-ton blocks ; and finally an 800-ton monolith of cement rubble, attached to the uppermost course of blocks by 3-inch iron rods. The whole mass—1,350 tons—was removed bodily by the waves, turned round, and dropped inside the mound; while the second course of 80-ton blocks was swept away like so many bricks. A 2,600-ton concrete monolith was substituted. Before it was two years old a storm shifted it and broke it in half ! Portland Harbour is probably the largest of all purely artificial harbours. It has an area of well over 2,000 acres to the one fathom line, and includes 1,500 acres of five-fathom water at low tide. The harbour is bounded and the famous Chesil Bank of Portland Harbour. by the land shingle on the west and north-west, and on the south by the island from which it gets its name. In 1849 a rubble breakwater was begun, running from the island in a north- easterly direction, and beyond it a second and much longer detached mound bending sharply northwards. Between the two was left a narrow passage for ships. The mounds, completed in 1872, were formed by running stones down a ropeway from the Portland quarries to a staging erected on the line of the breakwater, along which they were moved in trucks for dumping. The work was done by convict labour. To render the harbour fit for strategical purposes and able to protect warships from torpedo attack, two large additional break- waters, pointing south-eastwards from the northern end, have been added. The Bin- cleaves breakwater, 1,550 yards long, reaches out from the mainland. A second and iso- lated mound lies between it and the seaward extremity of the old island breakwater, there being a 700-foot passage at each end. For these newer works the stones quarried at Portland were delivered down a rope incline into barges, which dumped them on the line of the mounds, as had been done many years before at Plymouth. On the top of the mounds, which, have a bottom breadth of 285 feet and a maximum height of 57 feet, is a wall of ashlar about 20 feet high. The amount of material used in the 2| miles of breakwater was enormous. The Algiers breakwater is an interesting example of a mole built up largely of concrete blocks thrown in at random. The older part of the mole is composed of OK , , , . , , Algiers. 25-ton blocks heaped up on the sea bed. The newer portion was con- structed at less expense by bringing a flat rubble mound to within 33 feet of low- water level, and depositing the blocks on this base. The use of random blocks is economical, since less labour is required, and, as the spaces between the blocks equal one-third of the total volume of the heap, less material; but a mound so constructed would not bo suitable for sites where the waves are ex- ceptionally violent. The new defensive harbour at Gibraltar has an area of about 440 acres. It is protected by two moles running out from the shore and by