A Treatise On The Principles And Practice Of Harbour Engineering

CHAPTER V. STONE: NATURAL AND ARTIFICIAL. Stone Supplies —Qualities désirable—Density and Hardness—Weight of Stone—Obtainment —Mine Firing—Drilling Operations—Implements—Charging—Taniping—Firing— Fuses and Detonators—Seam Firing—Wedging—Blasting Agents—Description 0 of Quarrying Operations for Breakwaters at Goodwiek, Alderney, and Holyhead—Concrète —Its Ingredients -Their Qualities and Proportions—Sea-water in its relationship to Concrète—Model Spécification for Concrete in Maritime Works—Japanese Standards. Stone. Natural Stone.—One of the most important considérations in connection with the construction of a breakwater is the supply of stone. Even in the case of those breakwaters which consist mainly of concrete blocks, it is eminently desirable, from an economical point of view, to pack the concrete with as many stone burrs, plums, or displacers, as possible. And in mound breakwaters a plentiful supply of rubble is obviously a paramount requirement. The matter opens out into two branches. First, there is the quality of the stone, and secondly, the cost of obtaining it. The former question involves a considération of physical characteristics and chemical qualities ; the second, the proximity of a suitable quarry and the means of transport. Quality.—In regard to physical characteristics, there are two features of pre-eminent importance—density and hardness. Density, or high specific gravity, is essential, because, when immersed in water, a stone loses a very considerable part of its effective weight; and when the sea is in motion, its stability as an inert mass is thereby reduced to a very great extent. Further- more, if, compared with its weight, the stone possess a very large bulk, it presents a correspondingly large surface to wave action, thus increasing the scope or field of the disturbing force. These two factors of volume and weight must therefore be taken into joint considération ; they show that the smaller the surface area of a stone and the greater its unit weight, the less likelihood there is of disturbance. In other words, the higher the specific gravity, the greater the stability. A concrete example will perhaps render this fact clearer. Take two blocks of stone of the same size—say exact cubes, each containing one cubic yard—but with specific gravities, represented in one case by 3 and in the other by 2. In air, the weights are 5184 Ibs. and 3456 Ibs. respectively. 84