SEWERAGE SCHEME

Evening Post, Volume CXV, Issue 81, 6 April 1933, Page 9

SEWERAGE SCHEME

NEW PLYMOUTH SYSTEM

INTERESTING. ENGINEERING :..:..;•.■;■ ,"-':.'-.WpRK: •■■

The final phase of the work on tha difficult outfall pipe that enabled XeMr Plymouth's £172,000 sewerage schema to be put into operation- was successfully completed last week. Work was commenced on the scheme just over three'years ago, and now all but a small part of the reticulation work is ready' for use. - . ■ The scheme, which is an interesting feat of engineering, was a work o£ some magnitude. Thirty-three miles of pipes have already been laid, and tlia plans provide for a total of 44 miles. There are two largo . liquefaction chambers hollowed in the ground 55 feet " below the surfaco of Woolcombe Terraco,' on New Plymouth's seafront, ■ one 000 feet long and the • other 400 feet. Each is 9 feet high and 12 feet wide, and has been fully concreted. In addition, 3000 feeti of tunnelling had to be done to enable a connection to be mado to tho sub* urban reticulation. At one stage it was possible to "walk along a subterranean cavern beneath "New Plymouth for nearly a 'mile. ' ■

The most difficult task) 'however, was the construction of the outfall pipe to a hummock of rock 570 feet from th» base of the cliffs, which are reached by the sea at high tides. The construe* tion of a gantry upon a conglomerate rock foundation was accomplished a net done so thoroughly that it,'withstood a winter's battering from the westerly) gales that sweep the coast. As the work progressed into deeper water it could be. carried out only'at low water spring tides. The problem of the tides was solved to a certain extent by the con« struction at each spring tide of a coffer dam, which, was then pumped dry, enabling two' hours'- work to ba done at each tide. In that short spaea of time excavation, had to be done, pipes laid and set in concrete. Each spring tide that was favoured With, good weather saw approximately 30 to 35 feet of piping placed in position in the later stages, and the final length, was successfully completed .last Thursday. The success of the work was largely due to the . adoption of the modern method of driving steel sheet piling for the coffer-dams. Organisation also accounted for much, as is shown by the fact that on one occa« sion 119 bags of cement were mixed in the space of 90 minutes. Photographs of the work in progress appear among the pictures in. this issue.