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HYDEO-ELECTEIC WOEKS. Arapuni Power Development. The position at Arapuni on the Ist July, 1930, the beginning of the year covered by this report, was that all construction operations had ceased as a result of the earth-movement that took place on the 7th June. The position of the works at that time was that the power-house structure had been completed, with the exception of a few details ; and three turbines and generators, together with all the necessary switch-gear, cables, and transformers, had been erected and were in service. Measures to divert the surplus water from the forebay into the gorge by the construction of Nos. 7 and 8 penstock tunnels were well advanced, and preparatory work in connection with proposals to protect the rock at the falls in the overflow-channel was almost completed. No. 4 penstock tunnel was in hand, the excavation having been finished. Owing, however, to the serious position due to the damage resulting from the above-mentioned earth-movement, the Arapuni Lake had been emptied, and the station went out of service from the 11th June. Construction operations at once ceased, and were not resumed until December last. Investigations. —lnvestigations were immediately commenced as to the cause of the earth-movement. This work consisted of the clearing of a deposit of sand from the forebay, and the excavation of a series of small tunnels and shafts situated in the vicinity of the power-house and spillway structures : 4,334 ft. of drive and 208 ft. of shaft were completed for this particular purpose. Well-boring equipment was utilized to sink a number of investigation bores at the sides of the power-house, at the forebay, headrace, and main dam, a total of 2,404 ft. of deep hole being drilled. A technical committee, consisting of officers of the Scientific and Industrial Eesearch Department, the Director of the Geological Survey, and one outside geologist, visited the site, made a thorough investigation, and reported on the geological aspect of the movement. The whole of the information collected was then made available for Professor Hornell and Mr. Werner, two Swedish experts, who arrived at the invitation of the Government on the site at the end of the month of August, 1930. A thorough examination was made of the locality, of the conditions, and the nature of the rock ; and a report was subsequently made to the Government outlining their opinion of the cause of the movement and the nature of the remedial measures necessary to effectively, repair the damage to the works. Restoration Measures. —Professor Hornell's recommendations were accepted by the Government, and authority was issued during the month of December to proceed with the reconditioning of the station, when arrangements for the necessary staff and equipment were immediately put in hand. The major items of work were commenced on three shifts during January, and continued on that basis. By the end of the year —that is, the 30th June—the various works for the reconditioning of the headrace and forebay were well in hand. The lining of the overflow-channel with concrete has been commenced and the excavation preparatory to concreting the falls is almost completed. At the dam, grouting operations have been carried out on a large scale, and a commencement made with the excavation of a shaft for the emergency gates of the diversion tunnel. The reconditioning of the existing tunnel-gates is well forward. At the power-house the lower section of the foundation for No. 4 unit has been concreted and a start made with the erection of the turbine. No. 4 penstock tunnel is being lined, and the excavation required for the power-house extension had been recommenced. Details of the work carried out are as follows :—■ Penstock Intake Structure. —Eepairs are at present in hand, and as yet have been confined chiefly to the grouting of the rock comprising the foundation of the structure, and to the reconditioning of the damaged concrete by grouting and reinforcing with steel rods. This work is well forward. Drainage-tunnels. —The investigation tunnels driven from the water-level in the Gorge have been utilized as portion of a system of drainage-tunnels. A total of six tunnels, running at right angles to the line of the gorge and the headrace, have been provided for, and are situated at approximately 8-chain intervals between the up-stream end of the headrace-lining and the falls structure. These tunnels are provided for the purpose of draining the rock underneath the headrace, the forebay, and overflow-channel, and the block of country situated between those works and the gorge. The tunnels are nearing completion, a total of 6,960 lineal feet having been excavated. Reinforcement of Country at Junction of Penstock Intakes and Spillway. —This work is almost completed, and is being effected by the drilling, with special equipment, of a series of long horizontal holes up to 100 ft. in length, the inserting of steel rods into the holes, and subsequent pressuregrouting. Preparatory work in connection with the provision of a reinforcing concrete block at junction of spillway-weir and penstock intake structure has been finished. Crack in Headrace. —Strengthening and sealing the country along the line of the crack in the rock under the headrace and forebay has been in hand for some time and is almost completed. The work consists chiefly of drilling a series of 70-ft.-long inclined holes into the rock intersecting the crack below the surface, placing steel rods in the holes, and pressure-grouting. Headrace and Forebay Lining. —The preparation of the headrace and the placing of the special lining comprises one of the major works of the remedial measures, and consists of the clearing for, and construction of, side banks, the placing of porous layers, the laying of 35,000 square yards of bituminous mastic into which sheet iron is to be embedded, and the construction and laying of protecting concrete slabs. The preparation of the foundations for the new work was commenced with three shifts early during the month of January, and has been completed. Subsequently the construction of side banks was commenced, plough and scoop teams, supplemented by mechanical equipment, being used for the purpose. The construction of the banks is 85 per cent, completed.

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