PROBABLY LONGEST IN WORLD

Dominion, Volume 28, Issue 33, 2 November 1934, Page 11

PROBABLY LONGEST IN WORLD

New Lower Zambesi Bridge

NOTABLE ENGINEERING FEAT (British Official Wireless.) (Received November 1. 5.5 p.m.) Rugby, October 31. The Lower Zambesi bridge, which measures over 2i miles, and is probably the longest in the world, has just been completed. The bridge was started about 3i years ago. and has been finished well within the period of the contract by the Cleveland Bridge and Engineering Company, of Darlington. England, who also built the remarsable Victoria Falls bridge. The new bridge, which plays a vital part in the system of railways by which the N.vassaland protectorate is being developed, represents a notab'e engineering triumph, and numerous technical difficulties had to be surmounted in its construction. The superstructure of the bridge rests on 35 main piers of caisson construction in the bed of the river to a depth of 120 feet. The Lower Zambesi has been notorious as a malaria and blackwater fever area, but the mosquito control system inaugurated- by the construction company was so successful that during the whole three and a half years not a single case of malaria has occurred among all the European emiiloyees who were brought from England to work on the bridge. GREAT UNDERTAKING Necessity For Construction The bridge, which was to cost £1,500,000, is part of a larger scheme of African development and its erection was due to the desire of the British Government that the development of Nyasalaml abrl the neighbouring countries should not be hamstrung by lack of transport facilities for placing their products ou the world markets, stated “The Times 7 ’ recently. Up to the present to reach the port of Beira, produce has had to be ferried across the Zambesi in small boats or barges. From December to March the river is frequently in high flood and this sometimes entailed journeys of 40 miles for the ferry steamers. In the dry season the channels and sandbanks in the river Changed so frequently that endless additional labour was caused, even to the moving of loading points sometimes as often as once a week. Preliminary investigation of possible sites for a bridge, together with detailed study of the habits of the river, extended over a number of years. The available data on the behaviour of the river in the past was meagre, and extensive researches were made by the engineers, Messrs. Livesey and Henderson, in order to determine what was the highest flood level to which the Zambesi had ever risen. It is said that this

important factor was eventually to a large extent decided by-the level of the third step up to the front door of a certain barber’s shop at Sena, which was lapped by the waters during the record flood of 1840. Thia level, surveyed and calculated with the closest accuracy, and with a further allowance for safety, was taken as the height of the underside of the girders of the Zambezi bridge. Of the nature of the river bed nothing was known. During several years before the contract was placed the engineers were engaged in sinking trial bore-holea to determine the sort of foundation on which the "wells” supporting the piers of the bridge might rest. These investigations revealed very little rock in the bed of the river, which for most of its width consisted of a mixture of sand and clay. The bridge and its approach viaduct are just over 2j miles in length, nearly 2000 ft. longer than the Tay Bridge in Scotland. It consists of six approach spans of 66ft. Gin. each, 33 main: spans of 262 ft. Gin. each, seven smaller spans of 165 ft. each, and 18O5£t. of viaduct. Of the 34 main “wells ' or. caissons supporting the main piers, but few could be founded on rock, and the rest had.to be sunk into the sand and clay mixture which forms the bed of the river, to a depth sufficient to secure stability by “skin” friction; in other words, these “wells” had to be pushed into the river bed as far as they would go. Many of them reach a depth. of 110 ft. below lowwater level, and on top of them ate built piers 70£t. high to give the'Tieadroom necessary to permit the passage of small river steamers. Each of the piers and the concrete “wells” which support them contain about 5000 tone of concrete; some of them had to be constructed and sunk from pontoons moored in the stream, and skill of no mean order was required to ensure that these great cylinders, 36ft. long by 20ft. wide, were sunk dead vertical and not a fraction of an inch out of place. . As the piers were completed the steel epans were laid in place and riveted together. Every one or these spans had been previously fitted and marked at Darlington so that assembly in Africa might cause no difficulties. Each required about 20,000 rivets; .little difficulty was experienced in training raw African natives to do this work, using the latest pneumatic tools. Hundreds of thousands of natives on both the Portuguese and British shores of the lake, who before could never.hope to market anything, will find it worth while to grow ground nuts, cotton, rice, and other crops, with the proceeds of which they will lie able to purchase 1 products of English factories. The traveller, when he transfers from- the lake steamer to the train at Domira Bay. will make n rapid and journey to the liner alongside the quay nt Beira, without any vexatious delays for himself >r risk of damage to his belongings at the river crossing. It is indeed difficult to foresee the full economic effect of the opening of this new highway, but there can be little doubt that its influence on European and native life over a large area will be great.