A Treatise On The Principles And Practice Of Dock Engineering

’54 DOCK ENGINEERING. Granite is principally used in situations where great strength is required, such as tor copings and facings to dock walls, quoins and sills to entrances and locks, column and pivot bases, girder beds, paving setts, and road metal. The stone is procured in various parts of the United Kingdom, chiefly in Aberdeenshire, Kirkcudbrightshire, Cornwall, Devonshire, Leicester- shire, Wicklow, Wexford, and the Channel Isles. Cornish granites have generally a very coarse grain. Sandstone has a crystalline structure composed of grains of quartz cemented together by various substances, such as carbonate of lime, carbonate of magnesia, &c., upon the weathering qualifies of which the durability of the stone depends. A good sandstone should possess a uniform, compact, bright, well-cemented grain. A dull appearance is not a good sign. Some sandstones are very friable, others are but moder- ately durable, but a few of the harder varieties are very serviceable for dock work, such as those from the reputed quarry of Bramley Fall,* near Leeds, from the Forest of Dean, in Gloucestershire, and elsewhere. TABLE XIV. —Compbessive Strength of Stone.! Stone. Crushing Weight in Tons per Square Foot. Stone. Crushing Weight in Tons per Square Foot. Granite — Aberdeenshire, . 800 to 1,200 Limestone—Chilmark, 400 Cornish, 600 „ 1,000 Magnesian, . 430 Mount Sorrel, . 850 Sandstone—Craigleith, . 350 Trap—Penmaenmawr, 1,050 York, . 350 Limestone—Portland, 250 Bramley Fall, 390 Bath, . 90 to 100 Cheshire, 130 Purbeck, 580 Liniestone is a somewhat vague term for a stone, the principal con- stituent of which is carbonate of lime; and a class which includes chalk, Portland stone, Kentish rag and marble, has a very wide range of characteristics indeed. The most durable specimens, as a rule, are heavy, dense, and homogeneous, with a fine, crystalline grain. Portland and Purbeck limestones, perhaps the best known varieties in general use, differ slightly from this criterion ; the first has a fairly large grain, and the second is conchoidal and non-crystalline. Both these stones, and, indeed, limestones generally, and in a lesser degree sandstones, are vulner- able under the attacks of the Pholas, and this acts as a deterrent to their extensive use in marine situations. The limestone blocks at Plymouth * The original quarry of Bramley Fall is reported to be practically worked out, but niuch of the stone from neighbouring quarries goes by the same name. + For a very valuable and complète series of experimental results, dealing with the crushing strength of stone, the reader is referred to a paper on “ The Building Stones of Great Britain,” by Professor T. Hudson Beare.—Vide Min. Proc. Inst. C.E., vol. cvii.