UNEXPECTED WEAKNESS.

New Zealand Herald, Volume LXVII, Issue 20601, 27 June 1930, Page 14

UNEXPECTED WEAKNESS.

EXTENT OF MOVEMENT. RUPTURE AND BENDING. POWER HOUSE INCLUDED. LEAKAGE NOT INITIAL CAUSE. [BY TELEGRAPH. —PRESS ASSOCIATION.] WELLINGTON, Thursday. In his statement concerning the position at Arapuni, made in the House of Representatives to-day, the Hon. W. B. Taverner, Minister of Public Works, traced the history of the trouble from the time the cracks first developed. It was apparent almost from the first, he said, that extensive work would be necessary to make good the position and that- the ' plant would of necessity have to be shut 'down for a considerable period. The entire emptying of the lake was therefore decided upon. As soon as it became evident that it ;would be necessary for the plant to shut down Auckland was communicated with ind arrangements were made with the Auckland Power Board for it to take up its own load at its King's Wharf steam plant. Arrangements were also made to get steam on the department's steam set at the Grand Junction mine and also to ensure that the department's Diesel plant at Penrose was ready for immediate service. .. , Surplus Over Present Demand. ' It was also arranged that all power available from the McLaren's Falls plant, ;?which belongs to the Tauranga Borough .Council and from which the department . has in the past taken power over a considerable period, should be drawn upon. .Further, the Government's plant at Rotorua, Which has been shut down for some L time,' was also got ready for immediate "action. ' „ As a result when the water fell too low for the machines at Arapuni to operate •the load was taken up by the plants indicated, in addition to the department's station at Horahora, and has been carried jn this way ever since. t ; The total estimated power amount available is 19,150 kw., and the amount of the present load is 18,000 kw. Thus there is ..at present an estimated surplus of apvproximately 1150 kw.

Technical Committee's Eeport. The'director of the Geological Survey branch of the Scientific arid Industrial Research Department proceeded to Arapuni immediately after the trouble occurred, and after further examination when th» headrace was laid bare he consulted with the head of his department. The Minister in charge of that department agreed that a technical committee, consisting of the head of the department, Dr. Marsden, Dr. Henderson (director of the Geological Survey branch), Dr. P. Marshall (member .of the staff and at ono time professor oi geology at Otago University), and Professor J. A. Bartrum (professor of geology at the Auckland University College), should further examine the position and make a joint report. This they have done. !A summary of the report is as follows "A block of country near the, penstock tunnels, betwegn the spillway and the power-house, broke away at 1.30 a.m. on ' Juno 7, developing a crack extending along the front of the penstock tunnels , and spillway. Water poured into this crack, developing hydrostatic pressure, jivhich bent the block, including the poworhouse, progressively over toward tho river. 'This bending extended over two days the base of tho cracks filled up with grit, allowing fuller development of the / pressure. It is evident that tho block moved about a base woll below the river level, that is, some 300 ft. below the penstock bead.

Hydrostatic Pressure. ■ "Alter the diversion tunnel at the dam ■ ,was opened and the level of the water in iho penstock head began to recede, the block moved slowly back by about threequarters of its original displacement, and the leaks were reduced in greater proportion. It appears evident that the movement of tho crack after its original formation car. bo accounted for by tho hydropressure oi water entering tho .. cracks and the question naturally arises as to the origin of the original crack and or not further disturbances are ;>Jikely to occur. "Several alternative explanations may '•-Tbe advanced to account for the original . rupture:—Tho whole block of country may have been in tension from natural "causes and the extra excavation for tho new powerhouse, together with hydrostatic thrusts in the penstock head, may 1' Jravo just caused tho limit of resistance to jv bo overcome. This seems tho moro likely ..Explanation, "Alternitively, it is possible that water leaked into deep vertical joints below tho penstock head, developing sufficient pressure to cause a rupture. No evidence, can be found of such joints in sbe absence of deep borings. A thjrd posI

sible explanation is that the stress was caused by a possible earthquake wave which, owing to the fact that the powerhouse and penstock head were rigidly tied, mighfc possibly cause such a rupture. Against this is lack of observation of any such tremor. It is true that the initial movement of the block caused tremors and vibrations of the block which were observed by a man living in a hut near the penstock head. The cracks in the powerhouse, however, do not necessarily indicate a disturbance of the powerhouse foundations since they consist of a transverse crack of the whole building at the point where its width changes suddenly and cracks round te supports of tho heavy generators and turbines (350 tons). "The rock surfaces visible indicate no movement of rock masses relative to ono another. The whole occurrence might well be unforeseen and due to an unexpected weakness of the support of the whole block which has moved. This supporting material is only just strong enough to withstand the weight of the overlying rock without failure. Further buttressing of the whole block would appear necessary to prevent a recurrence of the movement and leakages of water from the forebay. "The geologists are of the opinion there was ho undue water percolation from the spillway into the block of rock between the spillway and the gorge and powerhouse previous to the formation of tho crack.' Thus the initial movement is unlikely to be due to this cause." Securing Expert Advice. The Minister added that realising the magnitude of the issues at stake and' also the uneasiness which had arisen in the public mind, the Government had decided to obtain the very best engineering advice that could be obtained and with that object in view had been in communication with tho High Commissioner for New Zeaalnd in London, the president of the Institute of Civil Engineers and organisations elsewhere in order to select the most suitable man.

"Until such time as the report to be made by this engineer has been received I have felt it my duly to advise tho Cabinet to discontinue any further works at Arapuni," he said. "Further investigations will include a survey of the financial position of the scheme and will deal with the economic aspect. In the meantime I wish to make the following observations:—

"The amount already invested in the Arapuni scheme, including substations and transmission lines and works in progress is £2,500,000. In the year beforo tho Arapuni scheme came into operation the working charges for the Waikato system amounted to £76,231 and tho standing charges for interest and depreci ation and renewals were £74,571, or a total of £150,802. For tho year ended March 31 last the respective figures were £62,702 and £195,752, altogether £258,454, so that tho difference amounting to £107,652 represented the additional total operation costs of Arapuni for tho year. The units sold for the year from the wholo Waikato system were 191 millions and the nett revenue after pavincr working expenses of £72,702 was £162,981. Over 6 Per Cent. Earned. "Tho average operating capital for tho year was £2,649,000, so that the net revenue over and above working expenses was 6.15 per cent, on operating capital, notwithstanding that tho plant installed was insufficient to tako the wholo of the available load during-tho earlier months of the year. The present installed capacity of the Arapuni station is 45,000 kw. and consists ,of three units. A fourth unit is now in process of shipment from England and had the course of events not been interrupted would have been in stalled on arrival, thus bringing the total capacity of the Arapuni plant to 60,000 kilowatts. "In a subsequent statement details will be given showing tho cost involved in calling into operation the standby plants and other stations which were required to take tho load when the supply ceased from Arapuni, but it may be remarked that the estimate at present for tho generating costs at those stations is at the rate of £85,000 por annum as against £12,000 for generating costs had Arapuni continued in commission.''

HORAHORA POWER. REDUCTION ON SUNDAY, Owing to repairs having to bo made to the screens »t the Horahora power station the supply of powor will be reduced, or, if necessary, cut off between 1 p.m. and 3 p.m. on Sunday. The Waitemala ElectricPower Board obtains its supply from Rorahora, but the diminution of powor during the slack hours on Sunday will cause no inconvenience to consumers. Tho screens which protect the turbines have been affected by the constant wear and tear, and to carry out tho repairs it is necessary to lower tho level of tho lako. RIVER LEVEL FALLS. ARAPUNI LAKE EMPTIED. [by telegraph.—own correspondent.] HAMILTON, Thursday. The Arapuni lake is now practically ompty and tho level of tho Waikato River ■at Hamilton has dropped 3ft. 6in. in tho last three days. A great deal of mud and silt is coming down and has affected the quality and colour of the water.