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Snow Sheds (2): Ferro-Concrete

How the railways protect their lines from the ravages of snow with costly snow sheds, the latest of which are built in ferro-concrete

CIVIL ENGINEERING - 16

NEW CONCRETE SNOW-SHED, Cascade Summit.

The ferro-concrete sheds in course of construction. This photograph conveys a graphic idea of

the steepness of the mountain sides.

THERE is another dangerous aspect which the engineer dreads. An avalanche, starting its travel from a point high up on a steep mountain side and travelling with fearful speed, may sweep over the shed, without inflicting any damage. It hits the bottom of the depression, but the momentum it has attained is so great that it rushes like a wave of Water for 100 or 200 feet up the opposite mountain wall. When its velocity is expended it drops back, and woe betide the line if it receives this backwash, as it were, for it will be battered to fragments. In some instances the snow-sheds even have been damaged and destroyed, not by avalanches which have rolled down from the crags and pinnacles immediately above them, but from slides which have descended the opposing mountain wall, have rushed across the depression, and have climbed the precipice on which the metals are laid, striking the snow-sheds from below, lifting them up, or breaking in the side and smothering the track.

While huge tree trunks and jagged masses of rock, weighing ten tons or more, are able to knock any human handiwork to smithereens, the “cyclonic wind” which accompanies the avalanche is equally destructive. The snow-fighters call it the “flurry”, but they fear it as much as the snow-slide itself. The faster the latter moves, the more terrifying the local hurricane set up. It not only follows immediately behind the moving mass, but extends to a distance of 100 feet or more on either side of the avalanche’s path, and is a whirlwind of fine particles of snow and other material which it picks up in its mad career. Often the flurry rises to a height of 100 feet. If the avalanche should be pulled up by some natural obstacle, such as the toe of the opposing mountain wall, the flurry rushes on ahead, following the line the slide would have taken had its movement continued. It tears branches away, uproots the smaller jack-pines, snaps off the tops of the bigger trees, and, bearing the wreckage onwards, finally flings it out on all sides. On one occasion a luckless railwayman happened to be caught by the flurry, although he was some distance away from the actual avalanche itself. He was picked up, spun round like a top, at the same time being lifted into the air and carried forward. When the wind had completed its frolic it dropped him, an inert mass, to the ground. His colleagues rushed to pick him up. He was limp and dead, although no injuries

were apparent. Not a thread was tom out of his clothes; no sign of a scratch on his skin, nor even a bruise was distinguishable. Yet when he was examined by the doctors there was not a bone in his body which was not either broken or dislocated.

The Canadian Pacific, however, is but one of the many railways crossing the North American continent which suffers from the devastation wrought by the snow-slide. In the United States the Great Northern Railway experiences almost as anxious and harassing a time during the winter season, especially where it saws the western slopes of the Cascades by daring loops. The mountain side, scarred by the galleries required to carry the tracks, are exceptionally steep, and the avalanches have magnificent uninterrupted runs. Their paths have been studied intimately, and at all points where such movements either occur regularly or are likely to happen massive timber sheds have been thrown up. As a matter of fact the line runs through long lengths of wooden tunnelling, which present a quaint appearance when viewed from the bottom of the valleys, resembling nothing so much as huge swallows’ nests perched high on the cliffs.

So thoroughly was the snow-shedding protection carried out on this length of line, that the engineers were almost convinced that it was impossible for a slide to catch the road. But engineering optimism and confidence received a rude awakening. The Great Northern Railway was swept by a slide which excelled anything which it had encountered previously, and which precipitated the biggest disaster ever recorded in connection with snow.

The winter of 1909-10 was one of the worst experienced in the history of this great undertaking. February and March brought a snowfall almost unparalleled, and the blocks not only were numerous, but of unprecedented frequency and duration. This particular line appeared to be in the heart of the snow zone of that winter; at all events it suffered more seriously than its contemporaries. The snow-ploughs were out from morning to night, and the gangs fought valiantly, but to no apparent avail. A west-bound passenger train crawled into the tunnel which burrows under the crest of the Cascades for some three miles, and reached the western portal. There it had to stop. The Fast Mail was in a similar plight. Its flight was arrested by the selfsame disturbing influence.

The avalanches roared down the mountains continuously. It seemed as if the gulch would be filled with debris brought down from above. The passenger train halted within the portal of the bore and

stood there, with its electric locomotives, for several hours. Then the passengers got fidgety. They dreaded an avalanche sweeping down and blocking their exit entirely. They approached the officials and begged that the train should pull out of the tunnel and down the line for half-a-mile to the town of Wellington, where they could stretch their legs. The train could not get through to the coast, as the line was blocked, although the snow-ploughs were toiling mighty hard in the endeavour to open the track.

The officials consented, and the train drew ahead to a point where the officials thought there was little danger of a slide descending upon the the line. Here the train stood ready to advance the moment the line was open, the passengers living and sleeping in the Pullmans. A few intrepid travellers, either fretting at the delay or having a premonition of disaster, packed their traps and decided to push afoot to Seattle. They wended their way carefully down the rugged white mountain side, struggling over snow 20 and 30 feet deep, to Scenic, then tramped along the grade for 12 miles to Skykomish, whence they took train over the open line to Seattle.

THE WELLINGTON AVALANCHE DISASTER ON THE GREAT NORTHERN RAILWAY, U.S.A. The largest single fragment of a car that was found.

The stalled train waited all day at Wellington, and the weary passengers at last turned into their berths. In the blackness of the night the snow started to move on the summits above, gathered impetus and weight, and tore down the mountain side, devastating the slopes over a width of half-a-mile of timber, loose rock, gravel and boulders. It struck the line where the passenger and Fast Mail trains were standing, picked them up and rolled them over and over a further 300 feet, leaving them in the mountain hollow buried beneath 50 feet of debris. Four electric locomotives also were caught in the slide’s embrace and were thrown pell-mell into the ravine. Several passengers had miraculous escapes, but a round hundred went to their doom.

No other catastrophe from snow can equal that of the American Great Northern Railroad. Its swiftness and magnitude staggered everyone. A fortnight elapsed before the lines were opened to permit trains to approach the point, although rescue parties toiled over the snow-garbed flanks in the effort to extend succour.

Among the first to reach the fatal spot were Mr. James J. Hill, the chairman of the railway, his son Louis, the president, and Mr. A. H. Hogeland, the chief engineer of the system. When they arrived the rescue forces were digging through the ice, rock, and tree trunks, striving to reach the mangled passengers in the splintered and pulverised coaches.

The officials tramped the track for miles and scoured the mountain sides above.

“Whatever the cost the track must be protected against a repetition of this disaster. If it means millions it must be done”, declared the chairman emphatically. “Start at once!”

The chief engineer completed his reconnaissance, and then returned east, preparing, during his journey, his designs for snow-sheds which would defy the avalanche. In order to secure impregnability during the ensuing winter, delays were dangerous, so by the time the chief had regained his office he had matured his plans, and was ready to put the constructional forces to work.

He decided to introduce a new type of snow-shed. Over half-a-mile of line, in a continuous length, demanded protection, and timber was out of the question owing to the fire danger. As an alternative the engineer decided to adopt ferro-concrete.

The rescuers had barely dug down to the wrecked train before large gangs of men appeared upon the track above, commencing operations for the erection of the huge structure which was to enclose the double track in a concrete tunnel. A matter of 3,300 feet of line was to be treated in this manner. All traffic was diverted over side tracks, so as to permit the workmen to continue their labours in gangs, day and night, without interruption.

A somewhat strange spectacle was presented during this work. The sleepy mountain town of Wellington — little more than a hamlet — was alive and bustling. The railway builders were setting the iron frames forming the metallic skeleton, the mixers were toiling incessantly preparing the gravel and cement, and the concrete as rapidly as it was mixed was dumped into the moulds, so that the structure was assuming its form with amazing speed. Down in the valley, where a few dirty patches of snow still lingered, were fragments and splinters of the train which had been hurled to destruction, while the mountain side was scarred with a wide swathe showing where the avalanche had mowed its way.

On the mountain side of the track the rock and loose earth were removed to permit of the erection of a huge monolithic bank of cement, armoured and reinforced with steel rods. On the opposite side, from concrete pedestals sunk into the ground, rose ribs of the same metal, a rod from each corner, and laced together about 12 inches apart. These were encased in wooden boxes into which the concrete was dumped and rammed tightly down, so as to form a homogeneous post of steel, cement and gravel. The tops of the posts were connected and interlaced with the steelwork forming the roof, which on the mountain side was anchored to the massive concrete wall. The latter is some 50 feet in thickness, and, being attached to the rock, forms practically part and parcel of the mountain. The roof of concrete, 10 inches in thickness, and sloping towards the canyon at one foot in five, is 22 feet above the rail level and covers both tracks. The reinforced posts are set 10 feet apart in the six-foot way, while others are anchored to the rear wall for additional strength.

By the time the work was completed some 30,000 barrels of cement and 2,400 tons of steel had been worked into the 3,300 feet of shedding, and £100,000 had been expended. An outlay of £30 a foot to protect the track against the ravages of the snow-slide conveys some idea of the lengths to which American railways will go in order to ensure safety to their patrons. The Great Northern Railway is proud of this length of snow-shedding, which the engineers maintain, rightly, offers as complete a protection against the forces of the snow-slide as human ingenuity at present can contrive. Confidence in the protective measures has been supported adequately by experience, inasmuch as the sheds have been subjected to terrifying bombardments, and have passed through the ordeals unscathed.

This innovation having proved so successful, other railways have adopted the ferro-concrete snow-shed principle. The Canadian Pacific Railway, after investigating the ferro-concrete structure, decided to introduce the principle upon their system in the Selkirks. The cost, however, would have been so prodigious that the possibility of avoiding the avalanche in its entirety was discussed and compared with the snow-shed method. As a result of these deliberations it was found that tunnelling through the Selkirks would not be appreciably more expensive, while greater security would be assured. Accordingly the Canadian Transcontinental Railway decided to drive the tunnel, which when completed will relieve the company of one of its most harrassing and expensive anxieties.

THE NEW CONCRETE SNOW-SHEDS, CASCADE SUMMIT. The reinforcing steel for the posts on the lower side of the line.

You can read more on “The Canadian Pacific Railway - 1”, “Clearing the Line” and

“Snow Sheds - 1” on this website.