TUNNEL SCIENCE

Evening Star, Issue 20555, 6 August 1930, Page 12

TUNNEL SCIENCE

. .—.— ASTONISHING GONTRASTS OLD AMD MODERN METHODS Modern railway tunnelling lias come a long way;;isince its first great triumph just fifty years ago, when tho St. Gothard tunnel, high in the Swiss Alps, was “holed through.” The first on which machinery had been used froin start to finish,- and-9.26 miles long—then the longest in the world—it set a record for speed, being finished in seven and a-half years. Coming directly on the heels of the previous world’s longest, the Mont Cenis, whieli took thirteen years to build—having had tho use of machinery only the last part of the way—the event made a great impression, the more so because, though a mile longer, the cost of the St. Gothard was only £1,940,■OOO, as against £3,000,000 for the Mont Cenis. To-day, in the light of tho improved methods how' applied, the wonderment over' that record changes to amazement that the tunnel was built at all under the conditions. It w r as a transition time,,of course, between the introduction of such machinery and the familiarity with the use of it. Little enough progress had been made in the actual handling of tho equipment, but the idea that reasonably good conditions should be provided for the work-men-seems hardly to have arisen. Explosives were just then being put to use for such work, as well as the new compressed-air drills, and they added a serious complication. Some twenty-six holes were bored jn the face of the rock to a depth of about a metre, which took about two hours. ■The holes were filled with dynamite, and the blast set off. That process sending out heat and smoke into tho tunnel and burning up what fresh air there was, had to be repeated regularly throughout the twenty-four hours, the men working in eight-hour shifts. Enough fresh air was expected to come from .the drills and from the locomotives which -were also run by compressed air, to furnish ventilation, but the amount was altogether inadequate. As tho work progressed the temperature rose and the air became more vitiated, until visitors were rarely permitted to enter because of the sheer danger of being in such an_ atmosphere, and the horses on tho job died at tho rate of ten a month. Tho scene in, tho scantily-lighted tunnel grew to ’resemble' an inferno, men going about naked in the intense heat. The story of tunnelling since that day has been as much as anything else a story of improvement in working conditions. Tho steps forward have not only had humane results, they have paid in working efficiency and in reducing the high labour turnover that accompanied disagreeable work. The very next largo tunnel built, tho AHberg, begun in ]SSO, introduced tho practice of pumping fresh air to the men, and the famous Simplon, begun in IS9S, introduced the idea of driving two parallel bores, connected at intervals, which facilitated ventilation, besides making -more economical construction. To-day the whole technique, considered from this point of view alone, has been overhauled. Holes for the dynamite charges are drilled deeper, so that the process goes on longer, and the blasts occur only about half fls often as before. Air, too, is piped directly up to the head, so that when tho blast lias taken place the fumes can he quickly blown out of the way. Men work in the tunnels to-day dressed in the same clothes that would be seen at any other Construction job. A second health problem that appears to have gone unnoticed in the day of tho St. Gothard was that caused by tho dust from the drills. The stone dust sent up into the air from the batteries of steel bars pounding their holes is responsible for an ailment known as “minors’ consumption.” A remarkable bit of ingenuity has largely overcome it; the drills

arc made hollow, and as they drive into the rock a small stream of water runs through them, which keeps the dust from flying. MECHANICAL MARVELS. Mechanisation of the tunnelling processes has been making notable strides in recent years. Tho famous Moffat tunnel in Colorado, opened in -1928, introduced the “mucking” machine. The “muck’’ Is tho debris from the explosion, which has to be cleared away to make room for tho drills. Formerly tho drills had been set up on cross bars, as hand muckers did tho clearing. Now a machine shovel comes into play, its great steel mouth scoops up a ton or so at a time, and the whole processes speeded up 60 per cent. This brought about a second big mechanical improvement. When a machine could dear the muck away so quickly it became a waste of time for men to move up tho heavy drills. Instead batteries of them—-usually of four —are now mounted permanently on a heavy car; tracks are laid right up to the face as soon ns tho wav is opened, an electric locomotive pushes the car up, and drilling is resumed within a few minutes. The men, moreover, are fresh when they start, instead of being already tired from bringing tho drills into place. A high degree of organisation has always been necessary to drive a tunnel, what with the need of keeping a small army of men and machinery supplied, but even here there have been striking advances. Careful triangulation has enabled the engineers to boro ,the tunnel in several places at once, and have them come together exactly as planned. The Cascade tunnel in Washington, opened last year, was built in this way. This is the largest on the American continent. A small separate tunnel, called a pioneer, was driven to one sidq and ahead of tho main tunnel, and cross tunnels were run over every 1,500 ft. Oesides tin’s organisation, which kept crews on several faces at once, the Cascade project introduced the process of radial drilling—that is, while one. crew was busy drilling holes into the face of the tunnel a second was following, boring into the top and sides to enlarge the opening.to.the desired size. With this organisation the Cascade tunnel fairly marched along. Its eight miles were completed in three years, and it made as much as 1,157 ft advance in a single month, and the usual rate exceeded 900 ft—which is a fair measure of the progress in tunnelling when compared with the average rate of the St. Gothard of 540 ft a month. Th same process of drilling on several faces at once has been introduced to oven greater advantage in Great Britain for n water tunnel sixteen miles long, twelve bores being made to tho lino of the main tunnel, so that, the driving could be done on twenty-four faces. So much at homo have engineers become now in handling tunnels that, compared with the early achievements, they seem to treat a mountain almost playfully. The latest long railroad tunnel, built in Italy on the lino from Florence to Bologna, and which is 11,3 miles long, has a railroad station 500 ft long in the centre of it, and two tunnels running off from it to provide side tracks. The use of tunnels for automobile traffic has given engineers a new problem in ventilation, because of the deadly carbon monoxide discharged in the motor exhaust. Since New York’s Holland tunnels solved this problem, an impetus has been given to underwater automobile tunnels elsewhere. One was recently built between Almeda and Oakland, Cal., which introduced the novel feature of sinking a chain of precast concrete cylinders on the river bed, and joining these. A somewhat similar plan is proposed for the Brnoklyn-Staten Island tunnel, and for parts of the tunnel envisaged across the Strait of Gibraltar between points on Spanish territory. Several deep underwater chasms have to bo bridged, it is said, and tho belief is that tubes can be thrown across, joining the tunnels which elsewhere would be dug under the bed of the strait.