Slow work that. The Northern Pacific finding its way through the crest of the Cascade Mountains by means of the great Stampede Tunnel, nearly two miles in length, demanded that the contractor work under pressure and make 13½ feet of tunnel a day. The contractor, working under the bonus plan, did better. With his army of 350 “hard-rock men,” “muckers,” and their helpers, and his tireless battery of 36 drills he sometimes made as high as eighteen feet a day from the two headings. On a three-year job he beat his contract time by seven days. The Northern Pacific paid the price, $118 for each lineal foot of tunnel. That was a high price, occasioned largely by the fact that the work was carried forward in what was then an almost unbroken wilderness. The Wabash finding its way through the great and forbidding hills of Western Pennsylvania to Pittsburgh a dozen years later was able to dig its succession of tunnels at an average cost of $4,509 for 100 feet. Of that amount $2,527 went for labor; and $260 was the price of a ton of dynamite.
When the tunnel engineer finds that his bore is not to pierce hard-rock, of whose solidity he is more than reasonably assured, he prepares to use cutting-shields. These shields, proceeding simultaneously from the portals and from the footings of the shafts, are steel rings of a circumference only slightly greater than that of the finished tunnel. With pick and with drill and dynamite, they constantly clear a path for it, whereupon it is pressed forward in that path. Dummy tracks follow the cutting-shield; and dummy locomotives—more likely electric than steam in these days—are used in removing the material. Electricity has been a boon to latter-day tunnel-workers. Its use for light and power keeps the tunnel quite clear of all gases during the work of boring.
In rare cases, the rock through which the shield has been forced is strong enough to support itself; in most works the engineers prefer to line the bore, with brick and concrete, as a rule. This lining is set in the path of the cutting-shield before its protection is entirely withdrawn; and so the heavy roof-timbering which was formerly a trade-mark of the successful tunnel engineer is no longer used.
Tunnel-boring becomes doubly difficult when the railroad is to be carried under a river or some broad arm of the sea. Men work in an unnatural environment when they work below the surface of great waters, and the record of such work is a record of many tragedies. At any instant firm rock may cease, silt or sand or an underground stream may make its appearance and the helpless workmen find a ready grave. In work where there is even the slightest expectation of such a contingency the air-lock, with its artificial pressure to hold back the soft earth and moisture is brought into use. In another chapter we shall see how the caisson is operated. Suffice it to say now that the necessity of “working under the air,” brings no comfort to any one. It vastly hinders and complicates the work of construction, and adds greatly to the expense. Moreover, it has its own record of tragedies. Still it remains, to the infinite credit of a national persistence, that there is no record in the annals of American engineering where the workers have finally given up a tunnel job. Lives have been sacrificed, good-sized fortunes swept away, but in the end the resistless railroad has always found its underground path.
The tunnel-workers can tell you of the accident when the subway was being driven under the East River from Manhattan to Brooklyn, three years ago. The cutting-shield, which was advancing from the Brooklyn side, suddenly slipped out from the rock into the unprotected soft mud of the river bottom. The heavily compressed air shot a geyser straight up to the surface of the river some fifty feet above. A workman shot through the geyser, pirouetted gayly for a fraction of a second above the river, then dropped, to be picked up by the crew of a passing ferryboat. In a week he was back at work again inside the cutting-shield. His fortune was the opposite of that which generally awaits a man caught in a tunnel accident.
“It ain’t as bad as it used to be,” one of them informs you. “When I first got into this profession, they didn’t have the electricity for lights or moving the cars or nothing. We used to try and get along with safety lamps an’ near choke to death. It was more like hell then than it is now.”
“Sometimes the construction engineer ... brings his line face to face with a mountain”
Finishing the lining of a tunnel