The cost of tirring in this case is exceedingly low, the rock being at the surface, with a few pockets of earth dispersed over the area operated on. The drilling turns out very well, considering the extremely hard nature of the rock. The cost of blasting is above the average; the character of the rock was such that in calculating the throw 10 tons of rock were considered sufficient for each pound of explosive used. The sledging is a heavy item, the material when blasted being of a similar size to that of the previous quarry (road-stone quarry No. 2), but the tough and stubborn character of the rock necessitated additional men being employed to break it up in order to keep the stone-breaking machine constantly at work. It may be mentioned that the rock in this quarry had defied the efforts of many contractors to put in a bore-hole, owing to the hard nature of the material. The jumpers could not be made to stand the work, 2 to 3 inches being all that it was possible to bore without resharpening. The appearance of the quarry face, when the rock drill was working and previous to blasting, is shown in fig. 90, and the amount of rock dislodged after blasting is represented in fig. 91. The cost of quarrying by machinery and blasting, as detailed on p. 170, is a mean result of working in twelve different quarries, including those just described, and may therefore be taken as an average in estimating the cost of quarrying in connection with the production of macadam. 226. All the quarries under the author's jurisdiction are worked during the summer months only, and in order to arrive at the cost when drilling and blasting operations have to be carried on during the winter season also, an allowance must be made for the short day inseparable from this time of the year, and for other circumstances. The cost of labour, which of necessity varies in different parts of the country, will also more or less affect the expenditure. 227. Cost of Quarrying by Manual Labour.-The cost of quarrying by manual labour, that is, by hand-boring, blasting with powder and fuse, including mashing or sledging, varies considerably, and may range from 10d. to 1s. 6d. per ton. For a small quantity of material, which is to be removed from the quarry in an intermittent manner, the cost of quarrying one ton of rock reduced to a size suitable for the hand-breakers may be taken at 1s. 1d. This figure, in order to make a comparison with the method described in the foregoing paragraphs, is apportioned to the several items which make up the cost of quarrying one ton of rock. The following sub-division may be taken as an average, although some of the items vary widely in different quarries. The price for such work is usually quoted and paid for at so much per cubic yard; the cost of quarrying one ton of rock, therefore, has been deduced from it. |