Rambles on Railways

by Sir Cusack P. Roney

The St. John’s Wood Railway, which starts from the Baker Street Station of the Metropolitan Railway, is in tunnel throughout, and is a series of stiff gradients, culminating with the stiffest of all at its St. John’s Wood end. The line is 2¾ miles long, and its total rise in this length will be 255 feet, but the elevations are very unequally distributed. Starting from Baker Street Station, it proceeds for a short distance on a level, and then it rises 1 in 90 and 1 in 44 to the Regent’s Canal. From the canal the line descends slightly, and then at three quarters of a mile from Baker Street will commence an ascent of 1 in 60, or at the rate of 88 feet in the mile, for 660 yards. Then follows an incline of the same length of 1 in 150 (35 feet in the mile), then for 440 yards nearly level, except, just for a few yards, 1 in 80. At one mile and 1,320 yards from Baker Street commences a gradient of 1 in 27, or 196 feet in the mile for a length of 1,320 yards. Half way up the gradient will be a station, but the steepness of the gradient will be diminished for about 200 feet to 1 in 250, or 21 feet in the mile. Mr. John Fowler, the President of the Institution of Civil Engineers, is engineer of the Metropolitan, the Metropolitan District, and the St. John’s Wood Railway Companies. The construction of an extension of this last-named line to Hampstead has been authorised.

The longest tunnel in Europe over land and over water is the Britannia Tubular Bridge built across the Menai Straits, parallel to and some mile and a-quarter from Telford’s beautiful Suspension Bridge opened for road traffic in 1829. It is 1,834 feet 9 inches long, and in fact consists of two independent wrought iron tubes, each placed alongside of the other. There are four spans, two of 460 feet each, and two of 230—that is, the tubes rest upon two abutments and three towers of masonry—at an elevation of 100 feet above high water mark. The tower called the Britannia Tower is built upon a solid rock that projects above high water nearly in the centre of the Channel. The summit of this tower is 130 feet higher than the level of the railway in the tubes. The total weight of iron in the tubes is 9,360 tons, each tube of 460 feet weighs 1,587 tons, each of 230 feet weighs 753 tons, but these weights of iron are greatly in excess of what would be put in tubular bridges of like spans at the present time; and for a length but little exceeding a third of a mile, one tube, and not two, would be considered more than sufficient for all traffic, in both directions, that could be conveyed through it. The tubular bridge across the Conway River, forty-five miles from Chester, consists of two tubes placed alongside each other, each is 400 feet long and 1,180 tons. The combined cost of the two bridges, Britannia and Conway, is always set down at a million sterling. Now-a-days they would be constructed for about half that amount.

But Canada, or rather the Grand Trunk Railway of Canada, can put forward the boast that it possesses the longest over-land-and-water tunnel in the world. The Victoria Railway Bridge is constructed across the River St. Lawrence just above the ancient city of Montreal. The entire length of this stupendous structure is 3,470 yards, or exactly 50 yards less than 2 miles. The tube is approached on each side by a solid abutment, that on the north side being 266 yards long, on the south 400 yards. Deducting these measurements from the total length of the bridge, the tunnel or tubular portion of it is 2,804 yards long, or 164 yards more than a mile and a-half. In addition to the abutments there are 24 piers of masonry which it is impossible to exceed in grandly massive strength and solidity. The current of the St. Lawrence runs where the bridge is constructed at a rate never less than six miles an hour, and in some parts of the stream its rate is ten. The real giant force, however, which the piers have to resist is the ice at its breaking up some time between the last ten days of each April and the first six or seven of each May. The late Mr. Robert Stephenson the engineer of this bridge, as well as those at the Menai Straits and at Conway, estimated the ice pressure on some of the central piers of the Victoria Bridge at six thousand tons each. It is therefore not to be wondered that there is no stone opposed to the current at each of these piers which weighs less than ten tons, and that all should be clamped together by massive bars of iron drilled into each block, and held fast for ever by molten lead poured into each interstice. The total amount of masonry in the bridge is 3,000,000 cubic feet, or about 22,000 tons. There are 25 tubes or spans of which 24 are 130 feet long each, and the centre, which is 60 feet above the surface of the water, is 242 feet long. The total amount of iron in the structure is 10,400 tons. The contractors for the bridge were Messrs. Peto & Betts, their resident engineer was Mr. James Hodges, and to him the chief merit in connection with the construction is due. Its cost was £1,350,000. It was opened for traffic at the period of the Prince of Wales’ visit to Canada and the United States in 1860.

So far as regards tunnels actually constructed. We now come to speak of tunnels suggested. These may he divided into two classes—tunnels under rivers and tunnels under the ocean. Of the former, the first to he mentioned is that proposed to he constructed under the Mersey, to connect its Cheshire and Lancashire sides together. The scheme is propounded by Mr. John Hawkshaw, the eminent engineer, in a letter which he addressed to the Mersey Dock and Harbour Board, on the 31st of August last. Mr. Hawkshaw having stated that it is evident a bridge or viaduct over the river would interfere with the navigation, whilst the sand-stone rock which underlies its bed affords facilities for the construction of a tunnel, proceeds to show that the river should be crossed between New Brighton and Bootle, that being the best point for connecting together the dock lines of railway on each side of the river Mersey.

The cost is set forth as follows:—

Total length of lines 9¼ miles; length of tunneling, 4,800 lineal yards: estimated cost £785,000.

The lowness of the estimate is owing to it not being necessary to pass through valuable property, or important commercial buildings of any kind. Nevertheless Mr. Hawkshaw feels that the usual allowance for contingencies should be increased from 10 to 20 per cent. on the outlay. Still it brings the total amount considerably under a million. Mr. Hawkshaw does not ask the Mersey Docks and Harbour Board to be at the total cost of these works, however important it is that the two several portions of the board’s establishment should be closely united in the manner which this tunnel accomplishes, but that it should only contribute a portion of the outlay—an outlay which he considers will not be more than a third of what will be required for accomplishing any other of the schemes that have been proposed for carrying a tunnel under the Mersey.

In 1864 the Dublin Trunk Connecting Railway obtained an Act for the construction of a railway in the immediate vicinity of Dublin. Part of the plan sanctioned by Parliament is a tunnel under the Liffey, less than half a mile from its mouth. The depth of the tunnel-top under the bed of the river will be 20 feet. The stratum of limestone rock is curiously placed where the tunnel is to be pierced. The bottom of it will rest upon the rock, but the tunnel itself will be constructed through the superjacent clay. It will be lined with brick in cement. Its length under the river is to be 324 yards, and the approaches to it, which are to be constructed in the manner known as “cut and cover,” are to be 430 yards each. The gradients on both sides will be 1 in 70, or 75½ feet in the mile. The cost is estimated by Mr. John Burke, the engineer for its construction, at £200 per yard forward.

A proposal has recently been made to construct a tunnel under the Humber from Barton to Hessle, close to Hull. A bridge over the river has often been spoken of; but its estimated cost, £700,000, render its construction hopeless. It is considered that the tunnel, which would be about 2,000 yards long, could be constructed for £150 a yard, and, with an allowance of £50,000 for approaches, the total cost would not exceed £350,000. It is not probable, however, that the railway companies concentrating on both sides of the river would find it to their interests, at all events at present, to carry this project into execution. The company that would most benefit by it would be the Manchester, Sheffield and Lincolnshire.