Engineering Wonders of the World
Volume I

176 ENGINEERING WONDERS OF THE WORLD. of large mines of gunpowder. A tunnel of about forty feet long having been driven square into the face of the cliff, cross-headings were run from the end so as to form a T-shaped ex- cavation. The ends of the cross-headings were then chambered out to accommodate from seven to ten tons of gunpowder, which was ignited electrically after the Great tunnels had been securely built up. Some of the largest mines of this kind tore off enormous masses of rock, the displacement at times being upwards of 100,000 tons. Blasting operations were carried on for some four years, in which period more than 2,000,000 tons of rock were, dealt with, the result being that an area of about 27 acres was made available for railway purposes, partly by removal of the cliffs and partly by tipping material out from the shore. The excavation was carried to a maximum depth into the cliff of 180 feet, and to a height of 200 feet for a distance of more than 600 yards. On ground thus formed have been constructed an exten- sive quay, a railway station, an electric generating station, offices, and general equip- ment of an up-to-date port. The exact form of the harbour and buildings is best shown by the several illustrations, reproduced by the courtesy of the Great Western Railway, and therefore this descrip- tion will be confined to the broader details of construction ; for it must be remembered, when considering the engineering features of a port, that the magnitude of its works, in the form of breakwaters, quays, etc., is probably ten times greater under water than above. Simultaneously with the excavation of the cliffs, the construction of the breakwater and other works proceeded. The The „ . A rock blasted down was loaded Breakwater. by steam travelling cranes into tip wagons, and conveyed over temporary railway lines to the various parts of the works. By far the greater part of the material wis required for the breakwater, the seaward side of which was faced with boulders weighing from three to fifteen tons. Stones of from one hun- dredweight to three tons in weight formed the harbour side of the breakwater, or were tipped to extend the space for qu-ay and sidings. Stones of less than a hundredweight were crushed for ballasting the railway lines, while the small chippings afforded material for mak- ing concrete blocks for the quay wall. Thus nothing was wasted. The breakwater, a huge mole 300 feet wide at its base and 70 feet at the top, rises about 70 feet from the sea-bed. On an average some 650 tons of stone had to be tipped for each foot of its total length of 2,000 feet. It shelters an area of 500 acres, and its top—20 feet above sea-level—is capped by a concrete parapet. At the present time quay space of over 1,110 feet provides berths for three vessels, the mini- mum depth of water alongside being 20 feet. The quay wall is by no means the least interesting feature of QUay the works. From its founda- Wall tions, where it is 19 feet 6 inches thick, it rises 50 feet, and in its con- struction some 5,000 concrete blocks, each weighing from 6 to 11 tons, and manufac- tured on the site, were used. ' To secure firm foundations a trench was excavated by a suction dredger ; a grab hopper barge fol- lowed, taking off the shingle down to the rock, which was then levelled by divers, any hollows being filled up with concrete in bags. In this way was obtained a perfectly level foundation, upon which a “ Titan ” crane was able to lower and set accurately the blocks—each of which had previously been allowed a period of three months to “ mature ” after the time of its manufacture before being placed in the wall. The quay wall was built of blocks to within three feet of high water, where it was 13 feet 6 inches thick. Above the block work the wall is of mass concrete, shaped in casings or