A NOVELTY IN BRIDGE-BUILDING.

Southland Times, Issue 1223, 15 March 1870, Page 3

A NOVELTY IN BRIDGE-BUILDING.

The ALyttelton Times thus notices a bridge in course of construction over the Rakaia, one of the most troublesome "rivers in this island- — When some few months agothe puT)lic were informed that the Provincial Government had accepted a tender from Mr William White forthe construction of a bridge across the Uakaia, it was not expected by those conversant with the details in any similar work of magnitude, that any great progress would be apparent for some considerable time. Ifor has there been, in fact, in the building of the bridge for wbich Mr White contracted any advance sufficiently special to warrant more than passing notice. It is, however, equally true that a bridge is now almost completed, which, in the interim, will be a very satisfactory substitutefor the more expensive structure. In casting about for some inexpensive method of securing the scaffolding necessary for jnle engines, the contractor hit upon the plan of driving tubes, such as are new so extensively used about Christchurch in artesian wells — gas-piping in fadt — and finding it succeed well the idea grew ; so, extending his operations, he -inserted them as piles from bank to bank, bwilt upon them, aud tbe restflt is, or shortly will be, a bridge fight, btft strong, and which may be cheaply and expeditiously strengthened, so as to bear any weight ever likely to test it. A tramway is laid, and there is ample room for foot traffic. It will be ready for use early in May next. There is nothing in its appearance or construction to distinguish it from an ordinary -very light tressel bridge, excepting the tubes, which are 16 feet long and 2£ inches in diamdter, driven from 6 to 3.0 feet into the ground (large shingle and boulders) according to level; they are single, six feet apart, boxed in, and three of them support Qaeh capsill. The tresseEng is of the lightest description, and is merely useful for bracing only, as the weight of the bridge is supported entirely by the tubes. The bays are 20 feet each"; the total length of bridge 1,280 yards, its width 12 feet. ! Of course, by doubling the tubes, by inserting intermediate tressels, and by trussing, the bridge may be stiffened to almost any extent, but it is supposed that it is sufficiently 'rigid and strong to meet aill present requirements. the water covered by the bridge is not more than one-eighth of its whole length, bnt when in flood, the river is often bank and bank. Since the understructure has been completed, several heasvy freshes have taken place, without affeetang "dts stability in the slightest degree. On the contrary, wherever the water has been in any I volume, it haß deposited shingle around each tressel, in some instances three feet high, and tailing out in their wake in narrow spits. The drift, which ia tussock, flax, Ac, has been allowed to accumulate before the tubes first dri*ven, withont any bad effect. ■ Mr White is not an engineer, we have his repeated assertions to that effect ; if he is, it as only in an interloping sort of way. He is, however a very disagreeable kind of a,*person, who has before, in his blundering amateur style, vicfested aU professional rules, maxims, and traditions, made and provided in that bebalf. The works he lias taken in hand have been mostly successful, but there are plenty who will clearly prove them to be wrong •in principle and execution — works, in fact, which ought not to be right in any i way whatever. It requires all onr ex- ' periences df the abominable " passage" _ of the Rakaia to persuade tra that a* bridge built of gas-pipes by such a person, *can possibly stand, or be safe if it ! does stand. Under the circumstances, it will, perhaps, be prudent to reserve our commendation till the success of this last innovation is proved.