WAIKATO IN BONDS.

New Zealand Herald, Volume LXIII, Issue 19383, 19 July 1926, Page 8

WAIKATO IN BONDS.

TRIUMPH AT ABAPUNI. DIVERSION OF THE RIVER. FIRST STAGE ACHIEVED. BARRIERS BROKEN DOWN. REM ARK A RLE BLASTING. The roar and crash o'f land mines which hurled rock 500 ft. into the air and made the cliffs quake to their foundations signalled a new phase of the Arapuni hydroelectricity scheme on Saturday. Portion of the river was turned into the diversion tunnel by the removal of the lip of the intake dumpling and by the explosion of over a ton of blasting gelatine the outlet dumpling was completely destroyed. It was one of (lie great events of a great engineering job and in the memory of the few people, not of Arapuni, who were privileged to see if, it will remain

as a thrill seldom experienced in civil life. The great explosion was highly spectacular, but it is only part of the event. The tension of the whole day, the final dramatic preparations, the waiting for the "zero" hour, the scene afterwards, the purpose of it all—these things go to the making of a wonderful memory. Small Change at Intake.

The operation did not go precisely to plan, bnfc it exceeded the brightest hopes. The charges in the intake dumpling (and be it understood it is a weighty dumpling) were limited to 14 of 101b. each, their purpose being to take about 6ft. from the top of it to allow part of the river to enter the tunnel. To this depth the clay was broken, but not dispersed, and hence there was no possibility of the tunnel filling in 60 seconds, as had been calculated. It was necessary to put a gang of men to work to open channels. These quickly scoured into rushing torrents, but it was an hour before the tunnel had filled up sufficiently to pour the water over the outlet dumpling, the removal of which presented the real problem of the whole job. Originally, it had been intended to blow up the outlet barrier first to make certain of an open channel before any part of the river was diverted, but the final decision was to turn in sufficient water to have its weight to aid in clearing the rock when it was dislodged and to create a cushion to help to take the shock that would be imposed upon the portal of the tunnel. Except for the delay in opening channels" at the intake everything went according to plan, and probably better. The Effect Localised. When the tunnel was full and the water was flowing over the outlet dumpling, the mighty charge was fired and so successful was its effect that when the smoke and spray cleared, a matter of about ten seconds, water was flowing where the huge barrier of rock had been and—a most important matter—there had been practically no dislodgment in the unsound country above. From the cliff-top the channel appeared as clean-cut as if made by hand. From the movement of the surface of muddy, flowing water it was evident that what remained of the broken rock was being swept into the fierce, deep current of the river, and in five minutes the movement of the water from the tunnel mouth indicated that it was running deep without impediment. The mining of the top of the intake dumpling requires little comment. Fourteen ordinary horizontal bores were put into the bank from the face of the excavation, which had an altitude of about 20ft. to river'level. In each of these bores was laid 101b. of blasting gelatine, and the effect in a sandy kind of clay can readily be understood. System of Mining. The system of mining the outlet was anything but ordinary and there professional interest lies, and it is probable that it will be the subject of weighty discussions in the engineering world. Acting under the personal guidance of Mr. Leggo, the Nobel Explosives Company's expert in New Zealand, the Sir William Armstrong Whitworth Company put down 64 vertical bores throughout the dumpling. None was less than 16ft. deep and the average depth was 20ft. Some had been driven with great difficulty into the face sloping into the river. In these bores pipes were placed and in each pipe many feet of blasting gelatine was rammed. Some of them had a charge 15ft. long. The explosive is very powerful, containing 90 per cent, of nitrate of glycerine. The detonant used was cordeau fuse, the core of which is that terrible explosive T.N.T., the detonating speed of which is 17,000 ft. a second. One Pound per Cubic Yard. Two wiring systems were installed, one in parallel and one in series. The charge was equivalent to a little over one pound to every cubic yard of earth and rock to be removed. Its total weight of over one ton has often been exceeded in the Dominion, but always large charges have been used to crumble quarry faces to the greatest possible degree. Here the reverse was the case. A channel, starting with a width of 24ft. and opening out like a fan, was wanted, and nothing more. This was achieved with wonderful accuracy. The largest charge has yet to be fired. Beneath the intake dumpling some 26ft. below the river level as it was before Saturday's charge, there is a gallery, the passages of which contain two tons of high explosive. With 6ft. taken off the lip there will still be about 20ft. of firm country above this charge and when the time is ripe, possibly during the next flood, it will be fired to complete the diversion of the river, a work which will be facilitated by the building of the gabion dam that will commence immediately. "It is best to take this river gently," said an cnginepr on Saturday. He said it without a smile. In spite of the volcanic explosion, he really meant it. He was explaining why the heavy lower charge in the intake dumpling had not been fired to turn the bulk of the river into the tunnel at once. For the moment it may be said that that wild colt, the Waikato, has been roped. A mouthing bit is between its teeth and soon it will lead quietly on a halter. Its day of labour is rapidly approaching.