Popular Science Monthly/Volume 83/October 1913/An Irish Channel Railway
| AN IRISH CHANNEL RAILWAY |
By HENRY GRATTAN TYRRELL, C.E.
CONSULTING ENGINEER, CHICAGO
IRELAND does not seem to have ever enjoyed so great a degree of favor and prosperity as other parts of Great Britain, notwithstanding the continuous efforts which, for centuries, have been spent in its behalf. This may be due to some extent to its isolated position and the presence of the Irish Channel which unfortunately separates it from England and Scotland. Money and lives have been freely given to secure political union and better conditions, and enormous energy has been expended to improve the social and commercial standing of Ireland and its inhabitants.
In the light of modern industrial development, the question may reasonably be asked: "Are there not other and more modern and rational ways of bettering Ireland, which, for centuries, has given and is still giving to the world many of its greatest leaders?" Viewing the problem of social and commercial betterment from the standpoint of the constructor or industrial engineer, it would seem that the policies which have been so generally successful in building up and uniting parts of other countries, should also meet with success here. Since the days of the Roman Republic, the building of roads and the linking together of separated states and provinces has proved to be most efficacious, and almost essential to commercial greatness. Realizing the need of road development, the Romans introduced their great policy of highway extension as their best and surest means of developing and uniting their great dominion. It is almost needless to say that the same policy of building roads and other channels for commerce has, for a century or more, been the most successful of all the means adopted for opening up new territory in America, Africa, Australia, China and other countries. The great railway systems of Canada and the United States, the canals at Suez and Panama and the systems of roads and inland canals in Great Britain itself, are evidences of profitable commercial extension due to the opening up of highways of transportation.
Considering the problem from the viewpoint of the engineer and builder, rather than from that of the politician or statesman, it would seem that a positive railway connection between Ireland and England should be of great advantage. The western island, with its population of five million people, still remains separated from England by a sea which requires several hours to cross, and though easily navigated, trade is greatly impeded by this water barrier. The advantages of a railway connection across the Irish Channel are many and easily understood. Such a railway would shorten the time for crossing the
Atlantic from America by a day or more, and develop terminal ports on the Irish coast, thereby enormously increasing the local commerce, and offering larger chances for employment and extended opportunities to its people. The Irish railways would, in fact, become the through routes from America to India and the far east, instead of being subordinated, as they now are, for local business from Liverpool and Glasgow. Railway traffic in Ireland would be further increased if a similar line crossed the channel from England to France, making through rail connection from Great Britain to the Continent. Under present conditions, ocean traffic from America to Ireland frequently goes first to Liverpool and thence back to Dublin or Belfast, with a corresponding delay. For local commerce between Ireland and the east, the time of transportation would be shortened by only two or three hours, and yet, for improving railway facilities from England to the north, the great Forth Bridge was built at a cost of $13,000,000.
One of the difficulties in connecting the railway systems of the Islands is the difference in their gauge, which is 4 feet 8½ inches, or standard width in England, and 5 feet 3 inches in Ireland. This difficulty could be overcome in some one of several ways, such as (1) transferring cargoes at the border, (2) changing all tracks to standard gauge, or (3) laying a third rail on both systems. Any of these methods would be costly, but a change would necessarily follow the construction of a channel road.
In selecting a location for the channel road, it will be found that the shortest distance across is from Tor Point in Antrim to the Mull of Cantyre, the length of which is fourteen miles, but this course would involve other difficult water crossings in Scotland, and the line would lead far to the northwest, making the course impracticable. A better location further south is that from Whitehead on the Irish coast, northeast of Belfast, to Port Patrick, the distance being twenty-three miles. An unfortunate feature of the latter course is the presence of a central valley or depression known as Beaufort's Dyke, the bottom of which is two or three hundred feet lower than other parts of the sea, which has a normal depth of 400 to 500 feet, making a total depth of 600 to 800 feet in this depression. Geologists declare that at one time there was no dividing sea, but only a central valley now known as Beaufort's Dyke, and during the Pleistocene period the land was submerged, forming the present Irish Sea and Channel.
There are at least four possible methods of establishing a railway across the channel: (1) a continuous embankment or causeway, (2) a submarine tunnel, (3) a submerged floating tube or viaduct and (4) a bridge.
A continuous embankment across the channel would cost at least $100,000,000, and possibly more, and it would interfere with shipping. It could be used for a double-track line of railway and for developing electric power from the strong northern current, which would be fifty times more productive of power than the whole Falls of Niagara. Such obstruction of the natural currents would, however, lower the water in the harbors of Glasgow, Liverpool, Belfast and Dublin, an objection of rather serious moment. Since the proposed causeway over to Scotland would lead in a northwesterly direction, the present water route to England and London would he shorter and quicker, and it is doubtful if the causeway would be practicable.
Investigations show that the best way of establishing a channel railway to Ireland is either by means of a submarine tunnel or a floating tube, the cost in both cases being much less than a bridge or causeway. The deep water of Beaufort's Dyke could be avoided by selecting a location from Laggan Head to Maiden Island and thence over to Antrim, or by bending the tunnel to the north around the end of this depression, and thereby increasing the tunnel length under the water to twenty-five miles, with a total length of thirty-five miles, including the approaches. A two-track bore, 150 feet below sea bottom, under water 500 feet deep, would probably cost $50,000,000 to $60,000,000 and the possibility of building it would depend wholly upon finding rock strata absolutely water-tight and impervious. Tunneling with compressed air to exclude water is possible only at depths not exceeding about 150 feet below the surface of the water, for then the atmospheric pressure reaches 75 pounds per square inch, and pressures and depths not exceeding half these amounts are usually enough for effective work. It is evident, therefore, that water could not be excluded by means of compressed air at the depth which would be necessary beneath the Irish Channel, and, as previously stated, the possibility of carrying on such work would depend entirely on finding impervious strata, the presence of which could not be definitely determined until the bore was made. The overhead thickness of rock in the Mersey tunnel is 30 feet, and in the Severn tunnel it is 40 feet.
It appears, therefore, that a tunnel would cost from $35,000,000 to $50,000,000, according to its location and other conditions, and would require from ten to twelve years for its construction.
Another method of crossing the channel is by means of floating tubes, lying either on the surface of the water or anchored far enough beneath the surface to allow ships to pass over out. While no structure of this kind has been built, somewhat similar submerged floating piers have occasionally been used, such as those under two swing bridges at Dublin, and the later one at Norwich, England. Very interesting designs for floating piers also appeared in a recent competition for a new bridge over the Hooghly River at Calcutta. The type is probably the most practical of all methods for crossing a navigable channel of so great a depth.
If the tubes were to float upon the surface, openings must be left for water travel, and this can be done by depressing occasional sections, four to five miles apart, leaving openings of 1,000 feet, the presence of the openings being indicated by signals. The depressed sections would connect with those on the surface by means of suitable grades. As the heaviest ships now afloat have a draft of about 36 feet, a depth of 40 to 45 feet in anticipation of increased draft, should be provided, as is wisely made in the Panama Canal. The roadway level would then lie about 60 feet below the surface, instead of down beneath Beaufort's Dyke, and the approaches would be proportionately shorter. In a submerged position they would not be subject to pressure from wind and wave, but would lie in comparatively quiet water. The chief objection to these tubes is their deterioration from rust, and the difficulty or impossibility of repairing them under water. When the metal is corroded through, the concrete or other lining would be the only remaining material for resisting external pressures. Since the tubes would be supported along their whole length, they would need a comparatively small section for strength, and if lying on the surface, the tubes would be proportioned like ships, to receive varying support, and to bridge the waves from one crest to another. The weight of the submerged tubes should be such as to nearly equal the weight of water displaced. If slightly less than the weight of water, there would be an upward pull on the anchors when empty, and a corresponding downward thrust under moving load, to be resisted by surface floats. If so arranged that the upward and downward pressures are equal, the forces under normal conditions would be a minimum, and the cross section of the tubes might be nearly or quite uniform throughout. The tubes would be made in convenient lengths of 200 to 400 feet, with their ends temporarily closed, and floated out into position and sunk to their desired depth, where they would be connected. The temporary dams should be 3 to 4 feet back from the ends, leaving space for the divers while bolting the sections together. A submerged viaduct of this kind across the Irish Channel could probably be built for $25,000,000 to $30,000,000, and the type is the most promising of all to put into execution.
Whether or not a channel railway would be profitable as a financial investment is uncertain, but it would accomplish a far greater purpose than merely earning dividends, for it would increase commercial activity in Ireland, and with government security for interest on the investment, it might in the end be one of the easiest means of bettering conditions there.
A high-level bridge over water of such great depth would necessarily be on floating piers, and its cost would be from $150,000,000 to $200,000,000—so great indeed as to be prohibitive.
The construction of a channel railway to Ireland, and a ship canal from Galway Bay to Dublin, the cost of which would be about $40,000,000, are of the utmost importance to the prosperity of the island and its people, for ocean ports would then be established on the west coast of Ireland, and this long neglected part of Great Britain would participate to a greater extent in the general welfare.