TUNNEL SCIENCE.

Auckland Star, Volume LXI, Issue 162, 11 July 1930, Page 9

TUNNEL SCIENCE.

ADVANCE SINCE ST. GOTHARD ASTONISHING CONTRASTS. FORMER TOLL ON LIFE TERRIBLE. Modern railway tunnelling has come, a long way since its first great triumph just fifty years ago, when the St. Gothard Tunnel, high in the Swiss Alps, was "holed through." The first on which machinery had been used from 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 yeare. Coming directly on the. heels of the previous world's longest, the Mont Cenis, which took thirteen yeare to build —having had the 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 £1,940,000, as against £3,000,000 for the Mont Cenis. To-day, in the light of the improved methods now applied, the wonderment over that record changes to amazement that the tunnel was built at all under the conditions. It was 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 the equipment, but the idea that reasonably good conditions should be provided for the workmen seems hardly to have arisen. Explosives were just then being put to-use for eueh work, as well as the new compressed-air drills, and they added a serious complication. Some twenty-six holes were bored in 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 the 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. An Inferno Created. 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 the work-progressed the temperature rose and the air became more vitiated, until visitors were rarely permitted to enter because v of the sheer danger of being in such an atmosphere, and the horses on the job died at the rate of ten a month. The ecene in the 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. The 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 large tunnel built, the Arlberg, begun in 18S0, introduced the practice of pumping fresh air to the men, and the famous Simplon, begun in 1898, 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 as often as before. Air, too, is piped directly up to the head, so that when the blast has taken place the fumes can be quickly blown out of the way. Men work in the tunnels to-day dressed in the eame clothes that would be seen at any other construction job. A second health problem that appears to have gone unnoticed in the day of the St. Gothard was that caused by the 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 "miners' consumption." A remarkable bit of ingenuity has largely overcame it; the drills are 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. The famous Moffat Tunnel in Colorado, opened in 1928, introduced the "mucking" machine. The "muck" is the debris from the explosion, which has to be cleared away to make room for the drills. Formerly the drills had been set up on crossbars as soon as possible and kept going while hand muckers did the clearing. Now a machine shovel comes into play, its great steel mouth scoops up a ton or so at a time, and .the whole process is speeded up 60 per cent. This brought about a second big mechanical improvement.- When a machine could clear the muck away so quickly it became a waste of time for men to move up the 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' soou as the way 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 the 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 bore the tunnel in several places at once and have th*em 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 side jmd ahead of the main tunnel, and cross tunnels were run over every 1500 feet. Besides this organisation, which kept crews working on several faces at once, the Cascade project introduced the process of radial drilling, that is, while one crew was busy driving 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. Playing With Mountains. With this organisation the Cascade tunnel fairly marched along. Its eight miles were completed in three years, and it made as much as 1157 feet advance in a single month, and She usual rate exceeded 900 feet—which is a fair measure of the progress in tunnelling when compared with the average rate of the St. Gothard of 540 feet a month. The same process of drilling on several faces at once has been introdiiced to even greater advantage in Great Britain for a water tunnel sixteen miles long, twelve bores

being made to the line of the main tunnel, so that the driving could be done on twenty-four faces. So much at home have engineers become now in handling tunnels that, compared with the early achievements, they seem to treat a mountain almost playfully.- Che latest long railroad tunnel, built in Italy on the line from Florence to Bologna, and which is 11.3 miles long, has a railroad station 500 feet long in the centre of it, and two tunnels running off :from it to provide sidetracks. 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 Alameda 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 Brooklyn-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 be bridged, it is said, and the belief is that tubes can be thrown across, joining the tunnels which elsewhere would be dug under the bed of the strait.