“The cover this week’s Part was made from a photograph supplied by the United States Bureau of Reclamation. It gives a striking view of one of the cableways used for transporting material during the building of the Boulder Dam, which was described in part 2.”
THE task of building a bridge or viaduct across a waterway frequented by small craft only is generally much easier for the engineer than when the waterway is used by large ships. In such conditions, to provide headroom for ships with a fixed deck bridge when the banks of the waterway are low is almost always out of the question. For one thing it would involve long and costly approaches to reach the desired height. With a low approach, then, some other method has to be adopted. The bascule bridge and the transporter bridge, described in the chapter beginning on page 381, are two types of bridge suitable for the purpose, although they have their limitations.
Examples of two other types are here shown. The upper illustration shows one of the eleven vertical lift bridges across the Welland Ship Canal, in Canada. As its name implies, the deck of this bridge is lifted bodily up out of the way when a vessel has to pass. This particular
bridge is situated at the city of Welland and has a 30-feet roadway. When closed the deck is only 15 feet above the water level, but when it is open it is about 111 feet above the water level. There is a clear channel 200 feet wide to be spanned and the length of the bridge, measured between the bearings, is over 231 feet. The deck is suspended at
the ends by wire ropes passing over large pulleys at the top of the guiding towers, counterweights inside the towers being attached to the other ends of the ropes.
The total weight of the lifting span and counterweights is 2,300 tons. The operating machinery is carried in a cabin situated centrally on the lifting span. Winches pay out and take in wire ropes and are driven by electric motors. The current for these is picked up by a shoe
travelling on conductor wires stretched vertically down the front of the towers. A petrol engine is fitted for use in the event of current failure.
The bridge shown in the lower illustration is of an older type, although it was completed in 1936. A span in the deepest part of the waterway is pivoted on a vertical axis so that it can be swung round to a position at right angles to the roadway and so leave a clear passage for ships at either side.
The bridge shown crosses the River Forth at Kincardine, Scotland, and its total length, with
its approach spans, is over half a mile. The swing span is 364 feet long and when it is open
there are two navigational openings each 150 feet in width; when closed there is a clear
headroom of 30 feet, at high water. The weight of the swing span is 1,600 tons and is taken
on sixty rollers arranged in a circular path. The control cabin is at the centre of the swing
span and the operating machinery is situated in the central pier. The machinery consists of
Modern industrial welding is a constructional method practised in workshops all over the world. Three principal welding systems are in use, the electric, the oxy-gas and the thermit process. Electric welding may call for temperatures as high as 7,500 degrees Fahrenheit. This chapter is by F E Dean, and is full of interesting explanations of the various welding processes that are used. The principle of electric resistance welding was discovered by accident when Professor Elihu Thomson was giving a lecture in the United States on electricity. One of the fascinating processes described is the metallization process, by which the most delicate of substances can be coated without injury. In this way it would be possible to put a glove of molten steel on the human hand without burning the skin.
Romance of African Copper:
“IN OPEN MINES, where copper-bearing ores are near the surface, steam shovels load the ore into railway trucks. The trucks are then hauled to the crushing plant where the ore is crushed and ground to a fine powder before treatment for the extraction of the copper.”
The exposed position of Dover made the building of its huge naval harbour a tremendous feat of engineering, calling for much daring and high organizing skill. Harbour building is one of the most interesting feats of the civil engineer. He has the sea to contend with, and the sea is a formidable opponent. One of the largest, and certainly one of the most important examples of harbour building is the National Harbour at Dover. Eleven years were occupied in this work, and the cost of it was about £4,000,000. The position of Dover made the work all the more difficult, because the port is so situated that it is exposed to the full fury of all gales ranging from extreme west to extreme east. In all about two and a half miles of breakwater and sea wall were built. The work is described in this chapter by Harold Shepstone. The harbour was opened by King George V (then Prince of Wales) on October 15, 1909. There is accommodation, in the enclosed water area of 610 acres, for a fleet of large warships and their attendant craft. The harbour works included the extension of the Admiralty Pier, which is used by the regular cross-Channel packets, to double its previous length, thus making it 3,200 feet long. An area of twenty-one acres, too, was reclaimed from the foreshore.
Despite enormous difficulties imposed by the nature of the country, which included steppes, rivers, lakes, mountains and desert, engineers at last succeeded in linking East and West with a steel highway across the largest stretch of unbroken land in the world. The article is by
C Hamilton Ellis and is concluded in part 16. It is the fifth article in the series on
“OUT INTO THE CHANNEL. The Admiralty Pier was extended seawards in the same way as the east arm and south breakwaters were built. On either side of the line of the future wall platforms were mounted on piles to hold the gantry and other cranes. On one of the gantries was mounted a temporary lighthouse which thus advanced as the wall was built.”
The Ruashi Copper Mine
“A LARGE OPEN COPPER MINE in the Belgian Congo. The Ruashi Mine, which is not far from the “Star of the Congo” and Elisabethville, was opened in 1922. This mine is an excellent example of the system of open working used when the copper ores are to be found near the surface. When the ores are at a greater depth shafts have to be sunk.”
Romance of African Copper:
“THE CONCENTRATOR PLANT at the N’Kana Mine, in Northern Rhodesia. The ore is first crushed to a powder and is then put in a vat of water. The water is agitated and a frothing oil is added. A film of oil adheres to the particles of copper and air bubbles form on the copper, causing it to float to the surface and leave the worthless matter suspended in the water.”
Building Dover Harbour
“LOWERING A CONCRETE BLOCK to the bed of the sea along the line of one of the breakwaters in Dover Harbour. The breakwaters were built of huge concrete blocks, laid on the sea bed and not on a foundation of rubble. The sea bed was first cleared to bedrock with the help of divers working in diving bells such as that shown on the platform to the left.”
The riches of the Copper Belt in Katanga, Belgian Congo, and of the copper mines in Northern Rhodesia have been won by the efforts of explorers, railway pioneers and mining engineers, who have built up an important industry in a district remote from the rest of civilization. One of the chief virtues of copper as a metal is that, except for silver, it is the best conductor of electricity. Its use, therefore, in this electric age, is extensive for engineering purposes. For thousands of years, however, copper was used as a precious metal and for decorative purposes. The word is derived from the name of the island of Cyprus, where the Romans obtained their copper ore. One of the richest copper-bearing districts in the world is the Katanga Copper belt in the Belgian Congo. Here are numbers of rich copper mines, and in this chapter Sidney Howard describes how the copper is extracted from the ore in the African mines. The chapter is illustrated with a photogravure section.
The N’Kana Copper Mine, Northern Rhodesia
“THE N’KANA COPPER MINE, in Northern Rhodesia, consists of a vertical central hoisting shaft more than 1,000 feet deep and a smaller but deeper vertical shaft for advance work. Adjoining the central shaft are the buildings, shown above, which house the concentrator and the crushers. The concentration process separates the copper from the worthless matter.”
Modified Tunnelling Shield
“MODIFIED FORM OF SHIELD, showing moving cantilever platform. The shield measured
19 ft 6 in inside the tail piece, and was advanced by sixteen 8-in hydraulic jacks. The pressure developed in the jacks corresponded with the amount necessary to force the shield forward, and varied according to the nature of the soil. The shield used by S. Pearson & Sons had been designed to deal with silt only. To make it suitable for working in rock an apron was built extending 6 feet in front of the face of the cutting edge.”
“OXY-ACETYLENE WELDING upon the cylinder block of a motor car engine. The operator is performing the delicate operation of welding a crack in a valve setting. In this process he works with a blowpipe which is fed with oxygen and acetylene - the two separate pipes can be clearly seen - and he uses the fierce flame to fuse into the casting the feed rod seen in is left hand. After the seat has been welded it is machined to match the other seats. The oxy-acetylene process is used principally for welding cast iron, but is extensively used also for welding steel, aluminium and other metals.”
“SIX STEEL SPANS carry the Trans-Siberian railway across the River Tom, 103½ miles along the route from Obi. The river here is 1,680 feet wide, and the six spans of 280 feet rest on masonry piers. The piers are reinforced by triangular buttresses pointing upstream, to break up ice that floats downstream in winter.”