TUNNEL SCIENCE

Hokitika Guardian, 19 July 1930, Page 7

TUNNEL SCIENCE

ADVANCE SINCE ST. GOTHAItD

ASTONISHING CONTRASTS

FORMER TOLL ON LIFE

TERRIBLE.

Modem railway tunnelling has come a long way since ks first great triumph just fifty years ago, when the St. Uothard Tunnel, high in the Swiss Alps, was “holed through.” The first on which machinery had been used from start to finish, and 11.2(3 miles long—then the longest in the world—it set a record for speed, being iinisned in seven and a half years. Coming directly. on the heels of the previous world’s longest, the Mont Cenis, which took thirteen years 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. Uothard was only £1,940,000, as against. £3,000,000 for ihe 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 tauditions. It v.as a transition time, oi course, IM-Mvten 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 ceeros 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 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 eighthour; shifts.

AN INFERNO CREATED. Enough fresh air was expected to come from the drills and from the locomotive?, 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 of the sheer danger of being in such an atmosphere, and the horses on. the job died at the rato of ten a month. The scene 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 work ing 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 1880, 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 dynamise charges fire 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 tuat when the blast has taken place the lunies can he quickly blown out of the way. Men work in the tunnels to-day dressed iu the same clothes tuai 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 overcome it; the drills are made hollow, and as they drive into the rook a small stream of water runs through them, which keeps the dust from flying.

MECHANICAL MARVELS. Mechan.ißa.tion of the tunnelling processes has been making notable strides in recent years, The famous iMoffat Tunnel in Colorado, opened in T 928, 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 l ,. Now a machine shovel comes into play, its great, steel mouth scoops up a ton or so . aft a time, and the Avlipie 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 qre laid right u|p to the fac© as soon as ..the way is opened, aii 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 lias 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 them come together exactly as planned, The Cns-

cade 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 cue Side and 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 organfsation the Cascade tunnel fairly maiviied along. Its eight miles were completed in three years, and it made as much as 1157 feet advance in a single month, and the usual rate exceeded 909 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 lias been introduced 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. The latest long railroad tunnel, built in Italy on the line from Florence to Bologne and which is 11,3 miles long, has a railroad station 600 feet long In the centre of it, and two tunnel? rum ning off from it to provide bid 6 * 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 Jtuilt between Alameda and Oakland, California, which introduced the novel feature of sinking a chain of pro cast 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, anjd the, belief is that tubes can be thrown across, joining the tunnels which elsewhere would be dug under the bjpd of the strait.