WAIKATO MASTERED.

New Zealand Herald, Volume LXIII, Issue 19390, 27 July 1926, Page 10

WAIKATO MASTERED.

DIVERSION OPERATIONS. SECOND GREAT EXPLOSION. INTAKE BAHlilEli BLASTED. POWERFUL CHARGE USED. PULL SUCCESS ACHIEVED. The second stage in the subjection of the turbulent Waikato River in the Arapuni gorge, was accomplished yesterday afternoon, when the intake dumpling was blown up with a charge of gelatine dynamite weighing over t\yo tons and a-haif. About half the river was immediately diverted into the tunnel. The explosion, which took place in heavy rain, was hardly, as spectacular as that which removed the outlet dumpling a week a so. The , charge was more than double the weight, although the explosive power per pound was less—-75 per cent, against 90 per cent.-—but the blast did not produce the same volcanic effect. Ihe reason was ill tbo man nee of laying the mines. At the outlet dumpling the charge was laid iu 65 perpendicular pipes, which cut a channel throwing the rock very high. Yesterday's charge was .designed to give greater .-expansion in the explosive effect. It coveted a greater mass of earth and the greater .part of it was beneath the bed of tho river,, and the charge, if used for quarry breaking, would have shifted 40,000 tons of earth. Yet no disturbance was done ill the towering cliffs of the gorge, the.only .damage not desired, being the collapse into the river of the jib of a steel crane directly opposite the tunnel intake. This is a minor matter, and will be remedied m a few days.

Confidence of Engineers. I<; was another day of crisis in the job. Half-done, it would have caused great difficulty. But there was not the same nervous tension as when the outlet dumpling was to be blasted. In the language of an engineer,.they iiad to make a dead bird" of shifting the lower dumpling before the force of the river was put into the tunnel. It was just as necessary that they should made a "dead bird" of the intake dumpling yesterday, but there was more confidence in the result —doubtless because there was less of the experimental about the method. Nevertheless, as shall be explained later, there were some unique features in connection with the charge. The dumpling had been riddled, deep down, with' drives and galleries, all prepared before the explosion of Saturday week, • when-a small charge broke up a surface layer,: 6ft. thick. This explosion, as was , related .in-the. Hebaud, did not disperse the material. By manual labour channels had to be- cut through it. • In the intervening week the water had scoured away all of the 6ft. layer except a portion in the centre, which formed an island in what yesterday was a foaming stream that dashed into the c .jin the. it was calculated, that the stream through the tunnel, which was taking about 20 per cent; of the river's volume of between 8000 and 9000 cusecs, was running at 6ft. a .second.

■ <'Fishing for the Taniwha." The reason for-this velocity in the tunnel- was-the complete clearance of the outlet... What the explosion had not done had been" accomplished during the week by mechanical means in the shape of a four-pronged grapnel. The stranges -who &sked what, was .happening when, the grapnel was working received the illuminating information from a flippant engineer—engineers occasionally can be flippant—that they were fishing for the taniwha , which,. according to the Maoris, lived, in the river and defied the engineers. The apparatus, under the power of compressed-air • winches, looked' a very simple and ineffectual contrivance, but it had" been far from ineffectual. The bottom of the channel had been thoroughly fractured' by the explosive. The force of the' -current: was' sufficient to sweep away hftgfc boplders as eooji as the grapnel had released them from the grip of the bed In this way a good 18ft.' had been secured from the tunnel-mouth to the deep channel of the river. They Had fished for a very "material taniwha with excellent'effect,-

ef" Galleries; Thus was set lor yesterday's explosion. - The drives and-galleries had been prepared long ago and a heavy difficult .job they made. A shaft 42ft. deep had been sunk from the ground above the old level and from its bottom a curving drive,- 135 ft. long and sft; by 3ft. had been carried directly uoder where the coffer had b-pen. . A second mam drive 90ft. long had been run more or less parallel on the cliff side. From these 18 galleries, of a total length of. -280 ft., had. been driven on a "stagger" system, those on the river side being right under its bed, but only Bft. below it, and the miners and electricians who worked in them could hear the stones*..; rumbling overhead as the swift surge swept them down. The miners who drove the .galleries, which measured only 2ft. 6in. by 2ft., had as bad a jol? as ever could : fall "to their lot—"cribbed, cabined and confined " and exceeding wet. Through this warren the mighty charge was distributed in 126 mines distributed in stagger formation and according to the amount of over-burden. The minimum over-burden above the main drives was 14ft. thick. Tins Filled With Dynamite.

The previous explosion had shaken down a fair quantity o£ earth into the galleries, but it was not necessary to remove it. "The roofs were propped and the workers crawled <through them with benzine tins filled with gelatine dynamite. Each mine weighed 501b.—451b. of gelatine dynamite and 51b. of blasting gelatine as priming. The whole worked out at nearly lilb. per cubic yard of earth, this heavy proportion being used on account of the "woolly" nature of the earth, which in geology is called tuff. Material offering more resistance—a tougher stratum—would have 'beer, an advantage. The wiring of the mines in these dark crannies' was a particularly arduous task for the electricians, who in some cases had to lie on their backs and even then had hardly anv elbow room.

Each mine had three electric detonators, two connected with T.N.T. fuse running through the charge and one direct into a plug of blasting gelatine. Thus a total of 380 detonators was used —a world's record. The wiring, which was to a 230 volt line, alternating current, provided for two phases and gave three circuits, two circuits carrying each detonator in parallel and one taking the detonators in series. Three-quarters of a mile of wire was used in connecting up the charges with the power. When the Wiring had been completed the drives were pumped full of water.to tamp the. charge. Three o'clock was the hour fixed for the explosion.,, and by that time a considerable crowd had gathered at the appointed grandstand .on the west side of the gorge 'jp-stream from the. intake. This , spot commanded a splendid view, but .no shelter, and soon the spectators . .were thoroughly soaked. . But that for the moment had not the slightest importance, X were prepared to pay for their. influen-T' " er "' s discomfort, cold and

Soon after three o'clock the hoarsevoiced hooter sounded its warning. Fifteen minutes later the five-minute signal sounded, and the seconds became tense with suppressed excitement. In the thick rain few saw the flag wave from the "0- Pip"—the observation station—occupied by the officials, and when the charge was fired ft »m the opposite side the eye was unable to telegraph its message to the brain quickly enough.

Where the little island hud been a mighty geyser aros?. The heavy report deadened by depth was hardly noticed, because the earth had begun to quake. Six definite tremors were felt before the white mass of the upheaval had subsided. It probably reached 300 ft. As it was falling a screaming noise was heard, and through the spray it was just possible to discern the cause —the falling jib of the gabion crane. The success of the explosion was evident in a few moments. The volume of water into the tunnel began to increase, and kept on increasing as the broken barrier began to feel the influence of the current. Five minutes afterwards if was estimated the tunnel was carrying 4000 cusocs, or nearly half of the flow of the river. For a little this was greater, some of the dislodged material having formed n bank in the river, but this was quickly swept awav.

The outlet end of the tunnel showed the result more plainly than tho intake. There the water rushed with great velocity, while the river itself between the two ends became a slow-flowing "boiling" stream. It still had volume, but ail the "sting" was out, of it, which is precisely what is desired. The gabion dam will do the rest.

Every hour for days the tunnel flow is likelv to increase, as the loose roe'\i are shifted by the current, but the i«b was really accomplished yesterday afternoon.