THE LONGEST TUNNEL IN THE WORLD.

Star (Christchurch), Issue 7416, 30 May 1902, Page 2

THE LONGEST TUNNEL IN THE WORLD.

MORE THAN TWELVE MILES. The radlway tunnel under the Simplon Pass, between Switzerland and Italy, is the biggest thing of its kind yet attempted (says the " New York Journal.") x A quarter of a century ago such a project would have been quite infeasrible. It dif-_ fers from the Mount Cenis, Mount Sfc Gothard, and Arlberg tunnels, not only in being longer, but alto in being a continuous rock tunnel, unconnected with the outer air by a single vertical shaft. | Its length will be 19,731. metres — more than twelve miles— as against 15,000 metres i for the Gothard, 12,800 for the Cenis, and > 10,300 for the Arlberg* On the other hand, it will be only 687 metres — less than 2300ft-r : above sea level, whereas the altitudes of the others range from 38G0ft to 4600ft. . This low elevation- avoids, the steep grades of the other lines, and secures for the approaches comparative immunity from 'snow blockades and: avalanches. At some points the tunnel will be more than at mile below the surface of the moan-, tain. This fact at once suggests one of the difficulties met with in the prosecution of the : work. The temperature ot borings, in level countries, rises a. degree for each 55ft of descent. In mountain borings the increase is less rapid, but the most favourable estimates predict a temperature of 104deg F. for the deepest part of the tunnel. In the central part of the Gothard tunnel, -where the temperature was only 88deg, the men could work only five hours a day, and had every third day off. \ : In the Simplon workings the temperature is lowered, and 1 the "air, vitiated by human exhalations and the smgke of explosives, is removed, by means jf ventilating pumps of 500-horse power, which furnish 3600 cubic feet of fresh air per second., The tunnel is being worked from both ends ; at once. On June 30 the Italian *nd had attained a length of 5000, the Swiss 4000 metres. It was begun on August 1, 1898. The date fixed for its completion, is May 1, 1904. The cost of actual construction is limited to 14,000,000d01, but auxiliary and unforeseen expenses will probably bring the total cost up. to 16,000,000d01. The Mount Cenis tundel cost, in proportion to length, just half as much again. The workmen employed number. 3500. The method of construction is original and ingenious. Instead of a double-track tunnel^ as at Mount -'Cenis and Mount; St Gothard, there will be two single-track tunnels, about 60ft apart. These are being pushed forward simultaneously, but only one of them is being enlarged to its ultimate dimensions, lined, and flnished.\ The other serves for the present as a. working tunnel, for ventilation, drainage, and the removal of rock. ( The tunnels are connected, every 200 yarns, by a transverse gallery. The large tunnel will at first be operated alone, and the small one will not be enlarged until the traffic shall warrant the outlay. Hence it has been thought necessary to provide for the meeting of two train's- on a singletrack road through the bowels of the earth by uniting the tunnels at their middle points, to form an underground station, where passengers, while waiting for the other train, may look "up^ at the roof and shudder at the thought that it is a mile thick. Hydraulic drills, working at pressures of from 70 to 120 atmospheres, are used in the Simplon workings. The rock is mostly gneiss and soft schists, which, permit a daily progress of five or six yards. There is hydraulic' mining of another sort, too, for after each blast the debris itr washed away by powerful jets of water thrown againsb the face of the workings. This use of water* while it adds to the humidity, greatly lowers the temperature of the air. Also, it sa-ves time, for the removal of rock, and the removal and replacement of drills takes much more time than the actual drilling. As it is, the drills work only eight hours in twenty-four, andTthey -^"uld work fewer hours, and the daily advance would bo much less, but for this ingenious use of water. Men and material are transported' by trains and cars drawn by locomotives, which enter the small tunnel, cross through. the transverse galleries, and make their exit by the large tunnel. With this exception the work is done by water-power, derived from the Rhone on the Swi«s, aud the Diveria- on the Italian eidt. The former supplies 1500, the latter 1700 horse power, and in the- future these rivers will furnish the power which, converted into electrical energy, will operate the tunnel railway.