THE TASK OF TUNNELLING

Taranaki Daily News, 14 November 1930, Page 9

THE TASK OF TUNNELLING

NEW PLYMOUTH’S SEWERAGE RAPID PROGRESS OF CONTRACTS. BURROWING UNDER THE TOWN. ' There is something almost romantic about tunnels. Certainly people think that down in the bowels of the earth life holds something that it does not hold)above in the open air. It is very different in the actual tunnels; it is unromantic to work in one. People peer dowii shafts and draw back with a pleasant thrill. For over half a mile at depths averaging 50 feet a tunnel has been drilled under New Plymouth during the winter. In another fortnight the tunnelling work will be completed and the final 200 feet of clay driven through. As an important part of the New Plymouth comprehensive sewerage scheme the tunnels branching east and. west from the foot of Eliot Street have attracted attention only by tlie framework, a shed or two, and mud and water at the three shafts sunk in connection with the work. The. houses ahd people underneath which the tunnels pass were not affected by. the drilling that has been going on underneath them at all hours. " It may rain or shine above, but down in the tunnels it is uniformly wet. Water seeps from everywhere. At the tops of the shafts pumps are busy forcing water away at the rate of thousands of gallons each hour.- It appears as if a small river has _ been tapped, but almost everywhere in the whole length water is seeping through porous soil. There is less in the clay, of course; everything, even the air, smells swampy when the fans have stopped. STREAMS OF WATER TAPPED. A stream of water seven inches deep runs constantly towards its lowest level and from the natural roof dirty water tries to dp the same, but by way of whatever pecks may be in the way. Anyone working in those tunnels, or merely paying ,a casual visit, wisely wears his oldest clothes and watertight footwear, preferably rubber thighboots, - . 7 - One splashes along in “follow my leader” style with a torch or a carbide lamp lighting a little of the gloom ahead. When the beam shines on the floor the novice forgets -the low ,ropf and knocks his head once again on a crossbar. Required changes in direction. and the construction of two liquefaction chambers, eastern and western, prevent the faint gleam at the other end that one associates with the tunnels of imagination. Compressed' air and a very simple but clever pneumatic pick, correctly used, ■carry , out in cramped space work that men with pick and shovel could scarcely hope to do. Through everything but rock .this pick bites, clay, sand and conglomerates, even a little peaty,coal. This last is down in Molesworth Street near Liardet Street. A few thin streaks of black stuff that oneb was timber and in a few thousand more years might have been coal, it shows in the halflight. Perhaps a forest covered this land, then swamp or sea, and then land again to a depth of about 50 feet. A frog was found in another part of the drive; it was a rather mysterious discovery. . Solid rock-.has been met with in a number of places, but the going has been fairly easy apart from the rock which gelignite has removed. The re-, maining 200 feet are likely to be elay all the way and present no difficulties. PRECISION OF This contract was commenced by the contractor, Mr. S. P. Stacpoole, on March sof this year. A shaft was sunk 60 feet deep at the foot of Eliot Street Hear the sea cliff, and from the shaft a tunnel was driven 200 feet up Eliot Street to' the point of intersection of •thd 'eastern' and western , liquefaction chambers, from which point tunnels were driven in’ two directions, one to near the East End reserve gates, where there is another shaft, and the western one to a point at the corner of Molesworth and Gover Streets. It has been continued at an angle down to Hawaii Street, with an opening at the shaft midway between Liardet and Gover Streets. i . Preparations ar ° being made to lay the large concrete pipes in the sections of tunnel already completed, and Christmas should see this work done. A layer of concrete ..will then be placed above the pipes for protection against earth falling in. The two liquefaction chambers are to be enlarged considerably before being finished. . . Straight lines are part of the religion of tunnelling contractors, and in this important work the borough surveyors have a part to play. At regular intervals they visit the tunnels and make fresh points for the men to work by. So far men working from opposite ends to meet each other have not diverged more than one-tenth of an inch from their measurements. . The theodolite has planned -the course and the tunnellers have kept to it religiously. An important section- of the work is the cutting of the outfall tunnel, a task that will be governed by the tides and the weather, and this will be one of the last parts of the contract. Almost a year remains for the completion of the contract, and at the present, rate of progress only half of that time may be required.