THE OPIHI BRIDGE.

Timaru Herald, Volume XIIC, Issue 13838, 25 February 1909, Page 2

THE OPIHI BRIDGE.

IN REINFORCED CONCRETE. It is'fully two months since Messrs C. and. W. Hall, contractors for the new traffic bridge at the- main road crossing of the Opihi river commenced work, but owing to the energy displayed, even now considerable progress lias been made with what may be called the preliminary work. As will perhaps be remembered, some time ago it was decided by the Geraldine and Levels County Councils that a newtraffic bridge over the Opihi was a necessity, and Mr Marchant was ' instructed to prepare plans, one to be for a new structure in wood, and the other to be of ferro-concrete, or as it sometimes termed, reinforced concrete. Messrs C. and W. Hall lost no time in taking the first sf;eps towards the erection of what will be, without question, one of the most substantial bridges of its kind in the Dominion. Judging from a somewhat cursory glance at the plans and elevations of the bridge, when finished, it will be a solid and ponderous looking, but hardly a beautiful pile. However, "handsome is as handsome does," and no one who has seen the preparations that are being made, and the massive materials that will be used in the construction of the work, can fail to realise _that it would be scarcely possible to erect a more time-defying, fabric than this ferro-concrete conception designed by Mr Marchant.

The new. bridge will rbe "built close alongside the old one, on the. upstream, or western side, and the concrete piles will be driven just about seven feet away from the piles that support the presfent structure, the work starting from the northern end. A slight deviation :in ■ the road and fresh approaches, to the bridge will have to be formed, but this work has nothing to do with Messrs' Hall, but will be undertaken by the Geraldine County Council, under the supervision of their foreman of works, Mr P. Billings. " Quite a little township has sprung up in the shelter of the branching willows on the north, bank of; the Upnu to the right of the approach to the bridge, and here dwell the twelve men at present- employed in the work of making the concrete piles that will support the- bridge, and in carting shingle and attending to the stone crushing plant that is at work, on the same side of the stream just below the old bridge. One who has not inspected the works can hardly realise the magnitude of the task involved in the contract. Some thousands of tons of concrete and steel have to be placed in position before the bridge is completed, and the shingle, of which the concrete is made, has to be carted from the riverbed to the crusher, graded into three grades, and again carted to the place where it will be mixed with cement to form the concrete. , The work on which the contractors' staff is at present engaged is the making of the reinforced piles, and an interesting process it is. First of all the shingle has to be procured, and this phase of the work keeps three 3-horse teams busily employed carting the stones, which range from the size of a man's hand to boulders two feet long,- to . the crusher. The riverbed has been quite cleaned of all the big surface stones for a considerable area, and now it is tound necessary to use a plough, to turn up fresh spoils. A great deal of trouble was experienced at first in getting the teams to draw up alongside the mill, as the horses seemed terrified, as well they might, at the roaring monster of . a niacnine which ate up cartloads of flint-hard boulders, and masticated them to tiny fragments, with 'the ease and gusto of a hungry boy surrounding a tart; but now* tne ' animals have gained, the familiarity that breeds contempt, and stand quietly alongside the crusher without a blink. \v hen the loads of stones have arrived at the crusher they are fed into ,it by two men, crushed, and ejected through a rotary grader, very much like the grain grader on a threshing •combine, whereby the crushed stuff is graded into sizes, Jin. to £in., iin. to lin., and lin. to ljin. The crusher that is being used is one of Hatfield's, driven by an 8 h.p. traction engine. It is ..not one of the rotary class, but pulverises the atones between two formidable serrated jaws, one of which is fixed, while the other, which is hinged in the middle, is worked by an eccentric and-made to play, upon' its fellow, with the result that the shingle is crushed, or pulverised by impact. The machine can keep three feeders going filling up the hopper with boulders. After being crushed the fine dust from the stone is blown to a distance by a powerful blast, just on the. same, principle as "a chaffey works on a combine. There is already a huge heap of crushed stone ready, estimated las containing 900 loads. ' The making of the ferroconcrete piles is an interesting process. For this the i to crushed stone is used to make the concrete. The core of the pile is a massive steel girder, with a section lik'e the letter H; round this is placed a wrapping of stout steel netting, not woven, but stamped clean from sheet steel. A wooden mould i*> built upon the ground, the steel core laid in it and then the concrete is worked well into all the interstices with specially formed rammers. The steel cores are 10 inches square and 38 feet long, 10 feet of which is left uncovered with the coating of concrete. When finished the pile measures 1(5inches square and weighs several tons. Before, the moulds can be removed from about the piles, several days have to elapse and six weeks before the pile can be driven.

A few words regarding tJie dimensions of.the new bridge, nui.v not be out of place :it this juncture. Its length is 940 feet; width'of high-way '2O feet; height of the railings, or .side guards from the roadway 4ft. !)in, There will be an iirched ro:id\vn,y of ferro-concreU' 7 inches thick, on the top of which will be placed an ordiunry tarred crown, such as seen in the iiiniii slrcefM of Timarn. H(!iivy braecH of Htcel rods run in all directions through the concrete, ensuring great ntrcntit/li mid iilmnlute rigidity; and there hciitji positively no material hut. hl.ci'l and concrete throughout the whole I'nhrii* should he practically everlasting. The lirrtl. of the 156 piles will be driven in about, a month's time and it is probable Unit it will he made the occasion of it eereinony of some kind. The plant for driving is on the ground, but as yet, it. i H mil, PT"ftedi An enormous 2 ton monkev will he the driving force and if will fall from a height of fifty feet. Sixtyone piles have, already hecn made, an average of about one a day, The

method of making piles described above results in producing a piece of work said to be tar superior to the, piles made for the ferro-concrete wharves in Auckland, where only four comparatively slender steel rods were encased in the concrete. Mr Marchant deserves credit for his design, and when finished the bridge Will be, without doubt, the solidest in New Zealand. No less ilo the contractors deserve commendation. It is good to see them at work, and they put in as hard an eight hours as any of the men working under their direction.