BOLTS SHAKEN OUT.

Auckland Star, Volume LX, Issue 228, 26 September 1929, Page 8

BOLTS SHAKEN OUT.

BY HUGE WATER PRESSURE. TESTS AT ARAPUNI. FURTHER STRENGTHENING NEEDED. WHAT INSPECTION REVEALED. (By Telegraph.—Special to " Star.") \ ARAPUNI, this day. More strengthening of the steel lining below the gates in the Arapuni diversion tunnel is needed before the gates themselves can be opened for a prolonged period to enable the unwatering of the spillway and the taking of steps to prevent further erosion at 1 the falls. This fact was revealed yesterday morning, when the gates, which had been partially open for 26 hours, were J closed once more, and an inspection of | the steel lining was made by Mr. T. Rabone, engineer in charge, Mr. A. Dinnie, of the Public Works Department, and the overseer. It was apparent that the steel lining in the tunnel must be more strongly iixeel before the gates can be allowed to remain open while concreting of the falls is in progress. The task of accomplishing this is not considered difficult, but any possibility of the lining being disturbed must first be removed. Therefore the gates must remain closed for an indefinite period while strengthening ■ work is vigorously pursued. The extra piecautipnary measures, however, should be completed in from ten days to a fortnight. I here is no need for hurry, as there has been no extensive erosion for six weeks. A gratifying feature of the tests is that the steel lining was less affected during the 26 hours the «ates were open than during the 12 hours ? t P «+ a fortnight ago. Only ten bolts out c f 840 were shaken out, and none of the welding between the steel sheets was fractured. An indication of the tremendous hydraulic pressure that the tunnel was subjected to may be had from tlie fact that the bolts extracted had nuts welded to them, and the heads were welded to the plate. Thus holts which

in ordinary circumstances would last an age, lose their grip under the terrific pressure in the tunnel. The intention now is to restore the bolts, and add new ones with the most exacting care.

Good progress is being made with the two new penstock tunnels that are being driven through to the powerhouse down in Arapuni gorge. The lower heading of the right penstock, has been carried 217 ft, or three-quarters of the way, and that of the left 80ft. Workmen are displaying much activity, as the order is urgent in regard to the tunnels. The second generator at Arapuni is now running interlocked electrically with the No. 1 unit. The effect of the additional generating capacity is to relieve Horaliora of part of its load, and to eliminate the subsidiary sources of supply at McLaren's Falls and the Grand Junction Mine, and also relieve the Diesel plant at Penrose- The third generator is expected to be in operation by Christmas.