Transactions . n blasted away. It was finally decided to adoptthe fissure as the line of the main gangway, and follow it to the end. MINING WORK. Work was begun on the main tunnel by two drillers taken fromthe quarry, and an open cut was made by them about seven feet inlength along the face of the old quarry, the loose rocks before theproposed mouth being thrown down the bank. The main differencebetween the plan of mining adopted and that used at Holyhead andelsewhere was that the shafts, instead of being sunk directly from themain gangway and the cross-cut gangways driven from the bottom,were
Transactions . n blasted away. It was finally decided to adoptthe fissure as the line of the main gangway, and follow it to the end. MINING WORK. Work was begun on the main tunnel by two drillers taken fromthe quarry, and an open cut was made by them about seven feet inlength along the face of the old quarry, the loose rocks before theproposed mouth being thrown down the bank. The main differencebetween the plan of mining adopted and that used at Holyhead andelsewhere was that the shafts, instead of being sunk directly from themain gangway and the cross-cut gangways driven from the bottom,were sunk from the ends of these cross-cuts, thus obviating the neces-sity of handling the rock twice, and of hoisting all the materialmined in the cross-cuts up the shaft. By this economy at least 50per cent, was gained in the driving of the cross-gangways. The main gangway was begun at a height of about fifteen feetabove the general surface of the quarry, so as to give some grip to 272 THE GREAT BLAST AT THE GKEAT BLAST AT GLENDON. 273 the tamping in tlie sluifts. After this gangway had been driven itsentire extent, tlie position of the powder-chambers was marked uponthe plan, and cross-gangways were driven to a point a little to theright, left, or behind them ; this was doneso that the powder-cham-ber would be by itself and not merely an enlargement of the bottomof the shaft. The shafts were then sunk to a depth of two feet belowthe level of the floor of the quarry in the direction of the line ofleast resistance, and the chambers were started and excavated to therequired size. The object of this slightly complicated system oftunnels, shafts, and chambers was to cause the tamping to gain asmuch resistance as possible to the force of the explosion, by the in-creased resistance caused by the friction of three right angles. As theexpansive force of the powder would bear upon the tamping, the firstresultant would act directly across the shaft in a horizontal line;the second
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
