Modern Gasworks Practice

CHAPTER II FOUNDATIONS, GASWORKS BUILDINGS, ETC. Emphasis has already been laid upon the advisability of securing a gasworks site which. is of low level in comparison with. the major portion of the district to be sup-plied. The works, however, will not necessarily be erected on the lowest-lying portion, as it may give rise to trouble in connection with water or bad foundations. Certainly, money may usually be saved in the first instance ; but unsuitable, spongy subsoils are almost invariably associated with land of this description, and untold damage may afterwards be occasioned by abnormal flooding. Nevertheless, in some cases other attractions may more than balance the prospect of an excessive expeiidi-ture on foundations, and gasworks have before now been erected on land reclaimed from the sea. Accordingly, the choice of the site must not be influenced by considera-tion of the immediate saving, and the various factors require to be carefully balanced before any hasty decision is come to. Before a site is definitely purchased, trial borings must be sunk, so tliat a fair indication of the substrata may be obtained. On an extensive site one such boring is by no means sufficient, as comparatively abrupt changes in the character of the strata are frequently found. The more general practice is to sink a circular boring about four feet in diameter, the sides of the excavation being shuttered up by means of a light wooden casing as the digging advances. The casings are usually worked in about 6-feet lengths. A less costly and laborious method consists. in driving down a special boring auger, which brings the core to the surface as it proceeds, thus enabling an accurate knowledge of the character of the subsoil to be obtained. An auger, complete with. the necessary boring outfit, is shown in Fig. 1. The first step is to sink a shallow pit 3 or 4 feet deep by about 4 feet squa.re. and to shiitter this up with timber. The shear-legs are then erected over the centre of the pit, and the boring rope is connected to the end of a special joint rod, to the other end of which the auger itself is attached. The auger is then drilled into the earth by a twisting motion, and periodically withdrawn by means of the windlass for the removal of the strata. The sketch shows a “ clay ” auger in use. It is found tliat with normal soils of the clay and soft gravel type a core of strata about 3 feet in length. may be brouglit up at eacli operation. In the event of the soil proving extremely hard, and of a rocky nature, a special tool of a chisel type is employed, and the strata broken up by a series of blows. Strata drills of this kind may be used for boring skafts of from 4 inches to 2 feet in diameter; for most purposes 40