SEARCH FOR LEAK

Dominion, Volume 25, Issue 274, 15 August 1932, Page 8

SEARCH FOR LEAK

Coffer Dam Finished at Arapuni BUILT IN FAST TIME Dominion Special Service. Auckland, August 13. The coffer dam in the Arapuni headrace was completed on Friday night, and to-day three pumps will be set to work to unwater it As this operation should only take four or five hours, it may be expected that the interior of the dam will be dry to-night. In view of the difficulties confronting the task, the dam has been built in commendably quick time, as it was only last Saturday that a start was made on its construction. Its walls standing 2ft. out of the water, the structure presents a very neat appearance. It is of exceedingly solid construction and the largest volume of water the headrace has. ever carried could not possibly shift it. As soon as the floor of the headrace inside th© dam is dry, a minute examination of the damage will be possible, and the access thus made available to the undermined bank may quite likely be of great value in tracing the course of the underground seepage which has caused the damage. Now a Placid Pool. The interior of the dam is now a placid pool, as unruffled as a millpond. ’ The water is deeply stained yellow owing to the large quantities of clay pug which have been poured into the trough of the wall to make it watertight, and an interesting, consequence is that the' water which >s leaking through the bent tiles Is emerging at the power-house, about a third of a mile away, stained an identical yellow. It is evident from this that the great bulk of the seepage now occurring. Is coming from the damaged portion of the lining, and when the coffer dam is unwatered, the leakage should be reduced to only negligible proportions. The search for the origin of the seepage above the cut-off wall is continuing more vigorously than ever, now that the concussion drill at the bottom of the recently excavated shaft has been set to work to supplement the efforts of the two well-borers. Horizontal Drilling. The drill is burrowing horizontally 40 feet underground in a direction away from the headrace through country not tapped so far by the wellborers. It has already driven a distance of over 40ft. without striking water and will next be turned round in the opposite direction to bore under the headrace. It is probable that other bores will be made horizontally in other directions before the shaft is sunk further and the bores duplicated at a lower level. A total of 13 vertical bores has now been sunk by the well-borers at distances of 18in. apart and it may be that scores of similar bores will yet be sunk in order to probe thoroughly the suspected country. Pres-sure-grouting will be carried out in each of them to seal the country against any possibility of percolation in the future.