OVER OR UNDER?

Evening Post, Volume CXXI, Issue 137, 11 June 1936, Page 10

OVER OR UNDER?

ENGINEER'S PROBLEM RAILWAYS AND RANGES CLUE TO RIMUTAKA - , (Written for "The Post" by 1.C.E.) The revival of the agitation over the Rimutaka railway and its famous (or infamous) incline opens up once more • some of the problems that railway construction engineers have to face and the principles and methods they have ,to ' adopt. If all New Zealand had been—for the purposes of railway construction —like the Hutt Valley or the Wairarapa Plain, there would have been no difficulty, and the engineers . could have gone straight ahead. But a mountain range intervenes and the . question is then how to get over it or under it. The engineer can do either. He can run his line over the slopes, easy or steep, of the range, taking ad-•-vantage of any natural easements in 'the topography. Or he can drive under the range in a tunnel. It is all a matter of cost—first cost and cost of running. A tunnel will obviouily cost far more than a surface line to build, but it will cost much less to work. In young countries first cost is the more serious factor; running costs, once the line is over the hill, can be left to posterity to worry about. This was the trouble with not only the Rimutaka, but many other parts of New Zealand When railways were first built. The idea, under the Vogel scheme, was Id build 1000 miles of railway with £5,000,000 of money. As this averages out at £5000 a mile, obviously there was not much room for long tunnels, whose cost is measured not in miles, but in feet. So the engineers had to cut their coat according tc* their cloth, and make the best way they could over the Rimutakas. Under the • circumstances a fair judgment would admit that they did not do so badly after all; The Fell system of the third rail was not at the time unique to New Zealand; it was employed on the Mont Anis line from France to Italy, on one of the main lines in Brazil out of Rio de Janeiro to mount the inland plateau, arid also on an electric railway up Snaefell in the Isle of Man in England, to mention only a few instances which come to mind. BUILD AND REBUILD, As time goes on and new countries develop, with constantly increasing traffic, the .question arises whether the heavy and heavier cost of _ working, apart from',the slowness and inconvenience of train travelling, does not justify some shorter and easier cut, costly, perhaps, to make, but. much cheaper tc run. A case in point and to hand ; is that of the Tawa Flat tunnels, one mile- and two and a half miles long respectively, under Wellington s west- , ern barrier of hills, built to save the cost of the existing heavily-graded, sharply-curved railway over the hills via Johnsonville. The volume of traffic, and the saving in cost of haulage are held to warrant the considerable capital outlay involved in •the tunnelling. Exactly the same process of reasoning caii be applied to the Rimutakas. If -the annual saving in time of transport and cost of haulage by reduction in grade and distance, measured by volume of probable traffic, is more than sufficient to pay for the extra capital ' required for the necessary deviation works, whether by single tunnel, new . route, and series of tunnels, or whatever the engineers decide, then the new work can be economically justified. The Tawa Flat tunnels and, deviation and a similar deviation into Auckland are so far the only out standing examples of the execution of such a policy in New Zealand: but there are many minor cases all over the Dominion, where the light railways originally laid down, when money was scarce and time abundant, have been adapted to modern conditions of faster and heavier traffic. EXAMPLES IN AMERICA. — Other new countries, notably North America, have had similar experiences. When the Canadian Pacific Railway spanned Canada in the eighties, the first objective was to get the line through to Vancouver as quickly as possible with the money available. The mountain barrier in this case was twofold, the Rockies and the Selkirks,* with the Columbia River between them. The C.P.R. went over the first by the Kicking Horse Pass and the second by the Rogers Pass. The grades between the two- were as high as 1 in 24—about half-way between the Rimutaka Incline and the Johnsonville climb. Four powerful locomotives were required to take an ordinary train-over and the wear and tear were terrific. Much of the route was under snow sheds to prevent snow-slides and avalanches from blocking or sweeping away the track. The C.P.R: some twenty years later, as the traffic warranted it, spent millions in all sorts of engineering devices—spiral tunnels and loops—to raise the grade to 1 in 50, and later pierced the Selkirks at Rogers Pass with the Connaught Tunnel, the longest in the British Empire, being a few feet longer than the five-mile Otira Tunnel, to save them five miles of distance and replace five miles of snowEheds. The summit level is 540 ft lower than the original surface line, but the grade even now is over 1 in 50. Similarly, across the border in the United States the Great Northern Railroad, to cut down its. grade over the Cascade Mountains, built a new tunnel 7.79 miles long, the longest in America, to supersede a more roundabout route • with a tunnel 2.63 miles long. The new Cascade tunnel was finished in 1928 at a cost of between £3,000,000 and £4,000,000. The new grade is about 1 in 75. Further south, in the Rockies, is the Moffat tunnel on the Denver and Salt Lake railroad, six miles long at an elevation of 9200 ft above the sea level, replacing a surface line with grades of 1 in 25. The cost was over £3,5 M,OOO. PIERCING THE APENNINES. These, are three salient North American examples of pioneer lines regraded by tunnels at heavy expense, justified by-the saving in time and haulage. An outstanding European example is the great Apennine tunnel, opened by Mussolini in April, 1934. The Apennines, dividing the populous industrial area of Northern Italy in the Valley of the Po with cities like Milan, Turin, and Venice, from the rest of Italy, presented a formidable barrier to railway transport. Three lines already existed, between Bologna and Florence, between- Garma and Sarzana, but the three together, with their steep grades end sharp curves, were quite inadequate to cope with the heavy and growing traffic. Work started on the new line —the "Direttisiima" as the Italians call it—in 1915, and was carried to a conclusion by the Fascist Government after the war. The new line is about fifty miles long and has a maximum grade of 12 per 1000. It involved very heavy engineering works, including viaducts and tunnels. The longest tunnel, 11.106 miles long, piercing the Apennines, is second only to the Simplon in the world's tunnels. About half-way through it. in the very hdart of the mountain, is a large station, wjth ample sidings and two lateral tunnels each 1980 ft long The whole line is electrified and the time saved

between Bologna and Florence is an hour and a half. The whole line cost about £17,000,000, and is a monument of railway engineering. Among other recent European tunnels is that under the Central Pyrenees between France and Spain, known as the Canfranc tunnel, obviating the journey round the two ends of the range where it- dips to the sea. These are just a few of the more remarkable railway tunnels constructed for the purpose of saving transport time and costs. There are, of course, great road tunnels, like those under the Mersey and the Hudson, and long and large tunnels for water as at the Boulder dam on the Colorado River in U.S.A. and the seventeen-mile tunnel under Ben Nevis in Scotland for Britain's greatest hydro-electric scheme. What has made these great works possible and economically feasible is the immense advance made in recent years in the technique and machinery of tunnelling. New Zealand has had ample experience with the Tawa Flat and Mount Victoria tunnels where the costs were less than was anticipated, and, at present, with the Homer Saddle tunnel on the new Milford Sound road in the course of construction. It is this experience that makes the piercing of the Rimutakas with a five-mile tunnel from Mungaroa to Cross Creek a less formidable task than it would seem. Tunnelling has progressed far lince the days of the Otira.