Sessional_Paper_1935 — Page 157

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Subsidiary Intakes, to intercept small streams en route, together with sand- straps fitted with washout pipes, have also been constructed, and a pathway for in- spection and maintenance purposes has been provided alongside the conduit for its whole length.

North Conduit.

The North Conduit which, under this section of the scheme, receives the dis- charge of the Temporary Conduit but will ultimately receive the draw off from the Gorge Dam, hitherto designated No. 2 Dam, forms part of the permanent works and discharges into the North Tunnel.

Construction was commenced in February and completed in December, 1925.

This conduit has been constructed of cement concrete throughout. It has a gradient of 1 in 1930, a length of 2,900 feet, and a capacity of 20 million gallons of water per day. Construction was somewhat difficult, due to the ground consist- ing largely of loose rock and the side slopes being steep, which necessitated several small retaining walls. In all other respects it is similar to the Temporary Conduit.

North Tunnel, South Conduit and South Tunnel.

These three items were carried out under one Contract. Preliminary Surveys, drawings and contract documents were prepared during 1924. The Contract was let in November of that year and completed in December, 1926. It was entrusted to the British firm of Sir Wm. Armstrong, Whitworth & Co., who installed modern plant and employed a large European staff for the work.

Owing to the difficult nature of the access to the sites of the works the Con- tractors erected overhead cableways for the transport of materials. One of these was provided from a loading station near the 7th mile-stone on the Castle Peak Road to an unloading station at the required elevation near the South Conduit and an- other cableway from a loading station near the 5th mile-stone on the Taipo Road to an unloading station near the South end of the South Tunnel.

By April, 1925, the Contractors had completed the erection of plant and housing accommodation.

North Tunnel.

Work on the North Tunnel under Smugglers Ridge, which receives the dis- charge of the North Conduit and passes it into the South Conduit, was commenced on the South face in April, 1925, and on the North face in December, 1925, the two headings meeting on August 9th, 1926, at a point 1,871 feet from the South end. The work was finally completed in December, 1926.

The rock throughout was generally of good quality granite, with occasional intrusions of shale, soft clay and running sand, which caused some difficulty, parti- cularly in the depositing of the concrete of the necessary arched roof lining.

The invert and sidewalls are lined throughout with 1.2.4 cement concrete. The invert has a minimum thickness of 6", the upper 3" of which is graded smooth with fine concrete. The sidewalls vary from 6" to 12" thick, according to the nature of the ground.

The roof is unlined except for 11 separate short sections aggregating 362 feet in length, in which concrete of a similar quality varying from 6" to 12" thick was used.

In one bad section, however, it was necessary to pack in rubble to a height of 20 feet, this being subsequently grouted solid.

The tunnel portals were finished in granite ashlar.