A TREMENDOUS EXPLOSION.

New Zealand Times, Volume XXXIV, Issue 5662, 23 May 1879, Page 5

A TREMENDOUS EXPLOSION.

(From the South Australian Register, April 22.) The first sensational blast at the Victor Harbor Breakwater works—and the largest ever fired in Australia—took place on Saturday afternoon, April 19, and proved a great success. The upheaval was a grand sight to wit-, ness, and between 35,000 and 40,000 tons of rock and earth were displaced. For months past this explosion had been anticipated with some amount of trepidation by the more nervous among the local residents, and with a good deal of curiosity far beyond the Southern districts. The charge consisted of five tons of gunpowder, or 10,0001 b., besides about 751 b. of dynamite. It was calculated that this would raise or displace 10,000 cubic yards, or 20,000 tons, of rook and earth. The tunnelling, drives, and chambers in which the explosives were stored were rather an elaborate and costly undertaking. They were almost in the form of a double-barred cross. The drives were all sft. 6in. in width, so as to allow three men to work in them, and at certain intervals there were powder chambers sunk sft. lower than the level of the drives. All the drives were horizontal. The main tunnel was 51ft. long, and from the end of it there branched off a very irregular T-head of a total length of 91ft. The explosives were not put in the drives, hut in five chambers branching off these—three off the T-head and two off the main tunnel about midway between the mouth and the end of the tunnel. About a ton of powder was placed in each chamber, and the whole of the charges were connected by a long ” sausage ” of dynamite in small cartridges. The powder was put in zinc cases, in order to protect it from, the effects of damp, and it was then stacked up in calico bags and covered with _ felt to prevent its being injured by drippings from the roof. Bach chamber was walled in with boulders of rubble, the walls being built about 13in. from the powder, so as to allow of a little expansion. The main drive and tunnel were then “ tamped ” or filled up with stones and dirt ” pressed home.” An electric wire ran through the tamping to a point about the centre of the T-head, where the detonator was placed at the end of the dynamite ** sausage.” The wire was about 200 yards long, the instrument —a dynamo-electric exploder—being placed that distance back from the south-east corner of the island where the upheaval was to take place. The " sausage ” connected all the powder chambers, and dynamite being much more rapid in its action than powder it was expected that all the charges would' go , off. simultaneously. The result proved the correctness of this anticipation, as only one dull heavy report was heard, ' The

tunnel was about 20ft. from the surface at its mouth, and at the T-head about 40ft. The vibration was not felt at all in the township. No cue heard the blast beyond Port Victor. Even where the firing party were—--200 yards away from the explosives—the vibration was a very slight one indeed. After Miss Robb had turned the little handle which did all the work a slight vibration was felt, then a second or two later the smoke and dust were seen, and four or five seconds afterwards came the report and rumbling sounds. The chasm left by the upheaval was something wonderful. Its immense dimensions startled every one who had seen the blow-up, and delighted the contractor (Mr. Robb) and his staff. The quantity of stuff displaced was between 35,000 and 40,000 tons, but unfortunately the rock was not of the best kiud, and there was a lot of earth amongst it. The whole mass above the drives had been lifted clean out of its position, and huge rocks from 50 to 100 tons (one was about 150 tons) in weight had been gently dropped down again a few yards from their original position. There were four or five blocks of about 70 or 80 tons each, standing not far away from each other on the further side of the great irregular gully which had been artificially formed. The chasm was about 100 ft. in leugth, and 30ft. or 40ft. wide, by from 25ft. to 40ft. deep. On the one side was the face of the solid rock—an excellent face that will serve as a capital start for the next big blast—and on the ocher was the disintegrated mass all hurled seaward. Towards the easterly side of the island a wall of rock was left standing, but it had no doubt been shaken, and will he more readily removed hereafter. Towards the southeast the blast had done all that was required, and a little more too. It had covered part of Mr. Robb’s private tramway on the embankment leading to the breakwater, and torn up some of the rails and twisted them like corkscrews. It had embedded about 150 ft. of the tramway beyond the 40ft. or 50ft. from which the rails had previously been taken up. But this is a mere trifle compared with the great advantage of having the stone so near the end of the. future breakwater.

The blast, and the preparation for it, are said to have cost nearly £IOOO. The powder alone was worth over £2OO (even at sd. per lb.), and the dynamite and other items brought up the value of the charge to more than £250. But even at the actual outlay in this instance the big blast has proved a most economic arrangement ; indeed, the saving is said to be a shilling or two per cubic yard.