PUBLIC WORKS’ SIGNAL WIN.

Putaruru Press, Volume VI, Issue 233, 19 April 1928, Page 4

PUBLIC WORKS’ SIGNAL WIN.

ON POWERHOUSE SITE AT ARAPUNI. Construction of Turbine House Begins. j Last Job of Great Undertaking. The Public Works Department has won the first round in the fight against nature on the much discussed power-house site at Arapuni. What was a few days ago a muddy, leaky hole, is now almost bone-dry and a picture of neatness and apparent e ficiency. Last week concrete was poured on to this job, and the actual construction work begun. Public interest in this immense hydro-electric undertaking will now be heightened, and proceedings expectantly watched, in the hepe that the Department will be able to crown their efforts by supplying power from Arapuni within the promised eighteen months. A bird’s-eye view of the powerhouse site, as seen from the suspension bridge some 300 feet above, now presents a wonderfully-different scene from that pertaining some few months ago. Then, the site presented an unkempt and forsaken appearance, oddments of machinery and other gear flanking or protruding from a muddy pond—shaped like a neglected swimming bath—which was situated at the foot of the great cliffs and separated only by a sandbagged embankment from the deep pools in the Waikato bed.

A Tidy Job. In this ugly state the site of four turbines which are to generate the much-needed electric power had lain for many months owing to the dispute between the contractors and the Fublic Works Department. Now all is changed, and where ugly chaos was enforced to reign, all is order and neatness. Of water, little can be seen inside the actual site area, and where a few weeks ago men were working practically waste high in slush, everything is now dry. An Epoch. Not only that, but the excavation work has proceeded at such a rate that the top-half of the site has been dug out over practically its whole area, to a depth of approximately 30 feet, and actual construction work on the power-house foundations has begun. This marks an epoch in the progress of the works at Arapuni, and reflects great credit on the Public Works Department’s staff, in that three months after talcing over the job of building the power-house on a site which has provided material for a battle of engineers, they have made such excellent progress. The question now remains: Can they continue the good work at such a rate that power from at least one turbine will be available within the next twelve months ? Draining the Site. For the present the Department is confining its attention to the upstream half of the power-house site, leaving the other half, which contains the unstable section of foundation for later attention. By means of channels sunk lower and lower an the excavation work went on, the 1 water was led to the foot of two j huge pumps capable of expelling | water at the rate of thousands of gal- ! lons per hour. As this greater depth I of excavation was secured, more and * more water poured through the sand 1 bag coffer-dam, owing to the fact that the water remaining in the river-bed is seven feet higher than was anticipated through the diverted river cutting across and forming a bank close to the mouth of Brandon’s pool.

Grouting Successful. This difficulty, however, was met by forcing at high pressure something like 300 tons of liquid cement through the cracks and fissures to effectively seal the bulk of them. So much so, that whereas the water formerly poured in at various different spots in the rude wall, now all that managed to percolate through is collected in- a double line of 12in pipes, laid in a ditch in the centre of the floor, and carried to a sump-hole from which it is quickly expelled by one pump, which when working at full capacity discharges at the rate of one cubic foot per second. Thus, through this grouting of the bank, work is proceeding on ground that is comparatively dry, as the pipe lines are laid below the floor level. So far this method of dealing with the situation has proved highly successful, though at one corner there is a weak spot, which occasions some anxiety, and which is being watched with particular care. Should an inrush occur here all preparations are in hand for dealing with the situation promptly.

A Monster Chute. Rising from the very floor of th® excavation is a gigantic chute which zig-zags its way to the top of the great cliffs, where the “ mix ” will be made.

Though the great ropeway is now demolished, some 20,000 yards of metal from Maku quarry—sufficient for all future requirements—has been dumped on the site of the giant hoppers by the great dam wall. From here a tram track has been laid across the top of the dam wall — which, by the way, is now open for vehicular traffic—and the little armoured engines will shortly be fully employed dragging trucks of metal to new hoppers which have been erected just below the step-up station. From these new hoppers a track runs down the steep hill-side and across the road to the edge of the cliff, where a concrete mixer has already been in operation. From the mixer the required kind of mix is fed to the mouth of the chute, whence it runs down some hundreds of feet below to be dropped by means of an easily moveable arm to the exact spot where it is required. Day and Night. In a very short while a constant stream of mix of the required coarseness will be pouring hour after hour throughout the whole day and night, down this suspended chute as the walls of the much-debated powerhouse arise. At present it is used but intermittently, only as the mix is required for the formation of the foundations.

This portion of the work naturally requires extra careful thought and attention, for it is over this work that the battle has raged. However, by means of liquid cement forced into the metal foundations at great pressure, and by extra heavy horizontal reinforcement, the Department is confident the weight of the powerhouse can be carried, as it will then be distributed over the whole area. This is the method now being adopted, as distinct from an alternative plan advanced by the contractors which would have involved a far more costly proceeding, and would have entailed the shortening of the penstocks.

Little to See. Though there is as yet little for the general public to see—with the exception that order has triumphed over chaos on the power-house site—at an early date there will be much of interest, as the walls of the building arise, and the huge turbine machinery and other generating gear is taken to the site and assembled in position. From the power-house site to Brandon’s pool the old river bed has to be deepened 25 feet, to allow the water after passing through the turbines to get away freely, and a start has been made on this work, by the removal of rock and debris in close proximity to the power-house site. POWERHOUSE SITE. Further Leakage. Early last week-end a big leakage occurred at the weak spot already noted in the sandbag embankment which serves as a coffer-dam around the powerhouse site. The flow, which is a fairly-big one, comes at a most unfortunate period, and some difficulty is experienced in coping with the water, which has flooded the excavation, owing to the fact of there being so much water backed up from Brandon’s Pool. As fast as it is pumped out the water comes in again because of the deep pools in the river bed. In all piobability a big pump will have to be set up near the sandbank at the far side of Brandon’s Pool in order to keep the old river bed dry and so draw off the water pumped from the powerhouse site.