The Railway Conquest of the World

by Frederick Arthur Ambrose Talbot

TWO VISITATIONS OF NATURE WHICH OVERWHELM THE CENTRAL ALASKAN RAILWAY PERIODICALLY.

As a rule it is mountains which offer a deterring barrier to the engineer, but in this instance it was the valleys which presented the most searching difficulties. The practical route for the line lay through the Placer River Valley, and the negotiation of this depression in order to preserve the grade and alignment was beset with innumerable perplexities. After leaving the coast the railway has to climb gradually until it gains and crosses the summit of the watershed at an altitude of 1,050 feet and 45 miles out of Seward. Then comes a sharp drop for 3 miles, followed by a more rapid descent for 200 feet or so. In times gone by a huge glacier filled this valley. At the head the ravine narrows sharply and leads into a canyon, where the rocky wall rises up on either hand almost perpendicularly to a height of some 700 feet. This rift is about three-quarters of a mile in length, and opens into another valley at the foot of a large glacier which leads to a bay on the coast known as Turnagain Arm. So sharp is the descent that in the course of 22 miles some 900 feet has to be overcome.

The drop from the summit at the 48th mile-post out of Seward for a distance of 6 miles puzzled the engineers sorely. Six surveys had to be run through this short canyon, and even then a grade of less than double the 1 in 50 was found impracticable. The configuration of the rift did not permit official requirements to be carried out with economy. Even the grade twice that demanded was found unattainable without six tunnels and seven large curves.

The survey was a perilous undertaking owing to the extreme steepness of the cliff-sides and the vegetation clinging to the rocky face. The rodmen working with the survey parties had to be slung in mid-air from ropes to enable the requisite calculations to be made.

The difficulties of the survey were surpassed by those of construction. The very first tunnel brought this home with startling vividity. It is 700 feet in length, and is almost entirely on a curve of about 400 feet radius burrowing through a projecting hump of the main chain. In order to gain the tunnel a broad sweep of the same radius as that of the tunnel curve had to be made, and the two works together form two-thirds of a circle. But one portal of the tunnel opens out on the brink of a precipice, the mountain-side falling away abruptly at that point. So in order to carry the line forward a huge artificial work had to be carried out. This is a timber trestle which constitutes one of the most outstanding features of the line. From end to end it measures 1,240 feet in length, while it varies in height from 40 to 90 feet, some of the outside members being no less that 120 feet in length. Over 1,000,000 feet of timber was used in its construction.

As a matter of fact, the extent of timber trestling upon this railway cannot fail to impress the visitor. In the valleys the line is laid almost entirely upon a wooden grade, owing to the absence of stable solid ground upon which to raise embankments, while the rivers are spanned by steel bridges ranging in span from 80 to 100 feet in the clear. As the rivers rise and fall considerably according to the season, the abutments had to be set well back from the low channel, and, moreover, had to be protected heavily by piling to withstand the severe scouring that takes place when the waterways are in flood and they rush along with the speed of a cataract.

More than 50 per cent. of the work through the canyon is tunnelling, which aggregates 2,800 feet out of 4,800 feet. There was no other way of overcoming the abrupt cliff-sides, and but for the rifts and clefts in their flanks its extent would have been greater. This was the work which occupied so much time and consumed so much money, for the rock was found to be intensely hard. Steam drilling was attempted at first, but the temperature within the borings rose so high as to become intolerable. Therefore this plant had to be discarded in favour of compressed air drills. With their aid a hole 21 feet in height, by 14 and 16 feet in width, to carry a single track, was hewn and blasted out.

The installation of the power plant to operate the drills was a pretty problem. It could not be set up on the same side of the canyon as the borings were being made, so had to be rigged up at a convenient point on the opposite wall near the upper end of the gorge, the power being transmitted through piping. In order to carry the latter across the gulch a temporary suspension bridge 130 feet long was erected, and as it was also employed for the purpose of conveying materials and men from one cliff to the other, was made heavier than otherwise.

In addition to perforating the shoulders of the mountains, deep clefts in the mountain faces had to be spanned or masses of obstructing rock had to be blown out of the way. In one instance there was a couloir which required a 90-foot span bridge to cross from one side to the other, while in another case 300 feet of solid rock, aggregating over 50,000 tons of rock, had to be torn down to enable the grade to proceed from one tunnel to the other. About thirteen months were required to carry the line through this stretch of 4,800 feet.

The struggles with the rock were equalled by the wrestles with Nature in the valleys. These are to all intents and purposes beds of rivers whose boundaries are the bases of the mountains on either side. As a result, the whole of the depression is practically a swamp, with the river cutting a tortuous path apparently through the centre. The word “apparently” is used because what is the main channel of the river to-day will be semi-dry land probably next year, because in the flood season, when the rivers are fed by melting snows, to speed along with fiendish velocity, they are just as likely as not to cut out an entirely new path through the soft soil. If the railway embankment bars its passage the whole obstruction is swept away. Hundreds of feet of completed line have been demolished in this manner. If the rushing river is unable to break through the embankment it swirls around the obstruction, rapidly undermining the foundations, with the result that a bad cave-in ensues, which is in every way as bad as a clean wash-out, except that perhaps the railway metals and sleepers can be retrieved.