Wood-Stave Pipe Replaces Steel

Press, Volume CVI, Issue 31115, 19 July 1966, Page 11

Wood-Stave Pipe Replaces Steel

When the import licensing schedule denied them ninefoot diameter metal pipes for deep culvert, Taranaki designers built the culvert in timber. What they created was a woodstave pressure pipe, similar to those which have oeen built in North America since 1870. The difference was that the culvert put in at Eltham had to be resistant to considerable outside pressure. In effect, the culvert is a treat wooden barrel, nine feet in diameter and 110 feet long The staves are 6in by 2in treated radiata pine, m-own in a plantation near Xew Plymouth. The culvert is buried 23 feet in heavy rock and earth fill. The verdict, after the job had been completed and fully tested, was that the idea was eminently practicable and economic. The costs turned out almost identical to those of the metal pipe—if that had been readily available. Experts are sure that the installation will last as long motal

The staves were machined to the required voussoir shape, the ends were squared, and the timber was treated with preservative. Formers were then laid in the bed of the culvert, and staves laid inside them to form the bottom of the pipe. While these were being clamped together, and nailed where necessary with galvanised iron nails to correct warping or springing, the internal formers were being made from Ijin diameter steam pipe. They were bent in semicircles, then set at nine-foot intervals in the curved trench formed by the base staves. Removable timbers acted as additional stays as the remaining staves were added Meanwhile, the filling process went on outside the growing pipe. Where required, the upper staves were held ir place with wire ties. The bottom part of the pipe

i was given the additional protection of a six-foot-wide coat of bituminous emulsion, followed by two coats of hot bitumen. The curve over the top of the huge pipe was negotiated satisfactorily, and finally the closure piece was dropped into position, like the keystone of an arch. When the backfill was brought up to the top, and some overhead weight applied, the pipe formers were dismantled and i j removed. The contractors said afterI wards that the most critical , j item in the series of opera- ■, tions was the filling. Pressure ; from the sides visibly dis- : torted the pipe as the fill , rose, and towards the end of > the operation, the top of the ’ culvert took on a Gothic arch s ; shape, until corrected by in--1 ternal bracing. 1 Experiments are proceed- » ing with factory-made smaller--1 diameter pipes, and with. a . semi-circular wooden arch > above a concrete base.