BIG SEWERAGE TUNNEL

Dominion, Volume 31, Issue 153, 25 March 1938, Page 13

BIG SEWERAGE TUNNEL

Inspection By Mayor And Works Committee NEW METHOD OF LINING Perhaps the most notable municipal, work now in progress in 'Wellington is the new sewerage extension scheme, for which the expenditure of some £200,000 was sanctioned by ratepayers about two years ago. The drainage facilities which sufficed for the city 40 years ago were discovered some 10 years ago to be becoming inadequate. Forty years ago the city streets were lined with one and two-story buildings; to-day six and eight-story buildings are being built, and whereas the buildings of 40. years ago housed only a few people, to-day’s large structures provide accommodation for a great many more. For that reason, plus the natural growth of residential 'Wellington, increased facilities have had to be provided.

In order to see the manner in which this work is being carried out, the mayor of Wellington , Mr.T. C. A. Hislop, and members of the works committee of the Wellington City Council, Crs. W. Appleton, chairman, R. A. Wright, P. Butler, R. McKeen, J. Read and W. J. Gaudin, accompanied by the city engineer, Mr. K. E. Duke, the town clerk, Mr. E. P. Norman, and the assistant city engineer, Mr. E. R. M Killop, donned blue dungarees and heavyweight gumboots in a little tin shed in upper Taranaki Street yesterday morning. The party was then driven to Drummond Street, off Adelaide Road, where they left the surface of the earth for realms below. Descent Into Shaft. There they descended from the golden sunlight of a perfect autumn morning into the stygian darkness of the earth. However, on their arrival on the floor some 20 feet 'below, electric lights were blinking in the gloom, casting reflections on pools of dull yellow water. Straight- ahead lay a line of dim lights receding into the distance. Having found that duck-boards paved the tunnel floor, members of the party stooped into the 6ft. by 3ft. passage and went forward: Interest was aroused by the electric lights used. They could be taken off the wire art any point and stuck on again to give light immediately, without the use of sockets and holders. Each lamp has two needle points, and these, on being clamped on to the wire, make contact with the live wire. The Method of Lining. The formation of the tunnel which leads from Drummond Street to Buckle Street, 80 feet under the National Art Gallery and carillon tower, was a major point of interest. Here the engineers have contrived a new type of lining. As the work of boxing for a concrete tunnel would have been awkward; arduous, and expensive' in such confined areas, a \way out had to be found. The result was a decision to have 3ft. reinforced circular concrete pipes cast in such a manner that a groove was left half-way up so that the pipe could be broken into two clean halves. The idea behind this was that the one half should serve as the floor of the-tunnel, the sides would be bricked up, and the other half-of-'the;pipe' should form the roof. ’■ This makes 'a neat and workmanlike job and practically ensures a tunnel that will stand up to certain strains in case of earth movement. It is the first time such an idea has been applied to tunnel-lining. Asked its to the formation of the ground, the city engineer said it was fairly good throughout, solid rotten rock for the most part, with . soft patches dripping with water here and there. These had to be timbered. Sections of both. classes of ground were seen by the inspecting party. The purity of the air wa.s a subject of comment. At one stage the city engineer announced that the party was about 70 feet below the level of Tasman Street, but the air was as pure and sweet as it was in the open. The reason for that was the air-compres-sion machlpery which draws the foul air out while the fresh air pours in continually by the various shafts. The party descended into several of the shafts, some of which showed two- , way drives, but the experience was much the same in each instance. Ultimate Extent of Tunnel. The tunnel will ultimately extend, from Thorndon (Tinakori Road) to Newtown (Drummond Street) at varying depths underground. In some places it will be 90 feet beneath groundlevel, as at the National Art Gallery and Dominion Museum, but under the rising ground approaching The Terrace it will rise nearer to the surface, when it is possible that the “jacking” method of boring, as was used for the Cambridge Terrace culvert, may be employed, as it is quicker and just as efficient.

At Drummond Street thefe. will be a diversion tunnel, but the main flow of sewage will be conducted to the tunnel which pierces Mount ■ Victoria a little to the south of Government House. The construction of the new tunnel is the biggest civic work ever done in Wellington since the original sewage scheme was carried out under the direction of the late Mr.. Mestayer, and it is to the credit of that engineer that the system introduced on that occasion should have worked so effectively during the Intervening years. Before it is completed the present scheme will cost much more than the original one, but it is calculated by the city engineer that it will suffice for a city with double the present population of Wellington. “To me it appeared that excellent progress has been made with the work, and the conditions under which the work is being carried out show the greatest efficiency,” said the mayor after the inspection. “I was particularly impressed with that aspect of the big job and also with the fine type of men that are engaged on the work. It is certain that we and they should be proud of the manner in which we are building for the city of the future, as far as its sewage system is concerned.” (Picture on Pago 9.)