Eliminating the Weak Link

Manawatu Times, Volume 63, Issue 80, 5 April 1938, Page 5

Eliminating the Weak Link

GIGANTIC STRUCTURE OF CONCRETE For years a source of complaint from, motorists and a major problem for the Manawatu County Council, which before the Government took over the principal highways was the controlling body, ihc low-lying stretch of road between the Foxton Borough boundary and the Whirokino bridge is being raised by artificial means to a level that will place it above the highest flood waters that, have been recorded. Apart from the difficulties that have occurred through the roadway being closed to traffic by flood waters from the nearby Manawatu river, the peculiar soil formation over which the road must be taken, has always been a source of trouble. Built over a peat swamp which defied the elforts of engineers to secure a good foundation for the old macadam road, this section was a very weak link in a road which probably carries a greater volume of traffic than most in New Zealand. Constantly soaked by water in winter and dried by the summer sun, the road was an expensive proposition from a maintenance point of view. There came the time when the Whirokino suffered heavily by comparison with the sealed roads which run for mile after mile through the country- , side, and the Government in response to numerous deputations undertook to cany through the task as a national project. Tne original route was discarded in favour of a new one which takes a slightly more direct course. Boxes aud pits had been put down before this decision was made. It was recognised from the data made available that the embankment could be carried only a portion of the way to the Manawatu river and the original plan to carry it -to within 1450 feet of the river edge had to be discarded, leaving the section from the main drain, a distance of 3600 ft., to be spanned by a trestle bridge. The embankment has been completed for some time now aud work is being pushed forward on xhe construction of the mighty trestle bridge which will carry tne road high above the greatest known flood which is generally agreed to be the one experienced in 1902. Running parallel with the existing road formation but towering above it the bridge stretches from where the old highway leaves the main road to the riverbank —a distance of 3600 feet. This bridge over the land will comprise no fewer than ninety 40ft. spans and will be a gigantic structure of reinforced concrete. Already all the piles numbering 488 have been driven home, and down to a depth of about three feet a solid block of concrete tops them off. From this will rise the supports for the bridge proper. The piles represented quite a major task containing as they do 4940 cubic yards of concrete. Bach upright is not supported by au equal number of piles for every fifth one contains six instead of the customary live to allow an extra strong base to support divisions which will be made in the concrete to allow for earthquakes as well as normal expansion and contraction which is the usual practice in all large undertakings of this kind. In the small dividing place will be a layer of bitumen which will act as a cushion between the massive blocks of concrete. At present the progress of the contract has reached an interesting stage. From the end of the huge embankment which shears away from the old highway there stretch four rows of steel uprights in perfect line right across to the river. At the Foxton end a number have been boxed in preparatory to concreting and amid a pile of timber carpenters are busily engaged making the casings to carry the concrete around the supports. This in itself is a work of no small proportion calling for a large amount of labour. As all the concrete will have to be hoisted into position for pouring a device somewhat similar in outline to a gallows has been constructed and this will be moved along as the work proceeds. From now on the bridge will rapidly begin to take form and will be a source of interest to motorists who pass. Incidentally the pedestrian has not been overlooked and on tho decking of the finished structure will be two pedestrian refuges, each approximately onethird of the total distance from either end. Ample room will be allowed for traffic to pass as the width will bo 24 feet. A shorter trestle bridge has also to be built a portion of the way along the embankment, but compared with the mighty main structure this will be quite a small job. Nevertheless it is to serve a very useful purpose. Acting as a flood spillway it wil facilitate the outlet of water and prevent unnecessary backing up of water with a consequent inconvenience to the owners of the surrounding laud. A similar motion is partly responsible for the design of the trestle bridge, as even if an embankment had been feasible a rapid outlet would have been necessary to permit flood water to get away,