ACTIVITY" BELOW GROUND

Dominion, Volume 32, Issue 94, 14 January 1939, Page 8

ACTIVITY" BELOW GROUND

Sewerage Rehabilitation

In Wellington

TUNNELLING AND JACKING OPERATIONS Substantial progress has been made on the Wellington sewerage rehabilitation work since operations were begun early last year. The main intercepting sewer is now practically completed between the junction of Drummond Street and Adelaide Road and Martin Square. From Martin Square on to Vivian Street there is insufficient cover to justify tunnelling, and the sewer is being constructed in a special reinforced concrete pipe section, the pipes being jacked in short lengths under the city streets. t In the tunnel section the walls are made of concrete specially placed with steel forms and reinforced in the weaker country. The arch and the invert *are made of half-round spunconcrete pipes, ensuring verj smooth conditions of ilow. A total length of 3590 ft. of tunnel has been driven and practically the whole of this has been lined.

The jacking of the pipes under the city streets is a novel method which, so far as is known, has not been attempted elsewhere in New Zealand. The pipes are sufficiently large for a man to work inside them. He excavates the material away from the head of the driving face for a few inches, the pipes being then jacked up into position and excavation recommenced. The method has two great advantages. Interference with . the expensive surfaces of the city streets and disruption of traffic are reduced to a minimum. As a pipe occupies immediately the cavity made by the excavation, there is no danger to buildings by slips, and the load the pipe has to stand is very much reduced.

Tunnelling in Progress. At Vivian Street the sewer runs again into tunnel. A shaft has been sunk there, and tunnelling operations begun back toward the jacking section and on toward Dixon Street. At Dixon Street tunnelling operations are proceeding in. both directions, the northern leg toward a shaft in Church Street. From Church Street the tunnel proceeds to a shaft now being constructed at Everton Terrace, and thence to Sydney Street and on toward Grant Road. No work has yet been done past the Everton Terrace shaft. '

The finished tunnel will be 6 feet high and 3 feet wide. Through the jacked section a 3 feet 6 inch pipe is being driven. In each of the shaft heads modern electrically-driven equipment has been installed, and full conveniences are provided for the use of the tunnel workmen, the work proceeding throughout on two shifts. A considerable'amount of water seepage has been met with, as might be expected during the period of wet weather experienced during the last year. The going has been fairly straightforward but the prevailing rotten rock has been varied with soft patches of alluvial material in various section’s, which required, special precaution. Sixty men are employed on this section of the work. New Pumping System. The main sewer construction forms probably the most important feature of the rehabilitation work, but steps are in hand also for the improvement of the whole pumping system serving the low level areas of the city and suburbs. Four new electrically-driven air compressors are now in position at the old drainage pumping station, in the Clyde Quay Corporation yard and these have been tested on. load during the last two months. When further improvements are made to the pumping equipment it will be possible to carry the whole of the ejector load on these new units, and the elimination of refuse burning at the destructor has been commenced. Ultimately, separate provision will have to be made for the burning of a limited amount of specialized refuse, such as comes from ships, trade documents and so on. This will probably necessitate the construction of a small incinerator.