FIG. 137.—_Manchester Ship Canal Works, Runcorn._ ]
The way in which the difficulty is overcome of crossing the several busy lines of railway that intersect the course of the new canal, so that their traffic shall not be impeded, is one of special interest in this bold scheme. The London and North Western Railway crosses the Mersey at Runcorn by a bridge that leaves a clear headway of 75 feet at high water, and it was determined that this headway should be maintained in the bridges over the canal. The use of swing bridges on lines of railway over which trains are constantly passing being out of the question, it is necessary that the railways be carried over the canal at the required height. It is accordingly laid down in the Act of Parliament that before the Canal Company can cut the existing lines of railway it shall construct permanent bridges, and carry over them lines rising by gradients not exceeding 1 in 135, and not only so, but these deviation lines must be previously given up to the several railway companies for six months to be tried experimentally in that period for goods traffic. The cost of constructing these deviation lines, which, in all, will not be far short of 12 miles of new railway, will not be much less than £500,000. The traffic of the canal will probably have great feeders at certain points in the other canals and the railway lines that reach it. For instance, the Bridgewater Canal, now incorporated with the greater undertaking, will bring traffic from the Staffordshire potteries, the river Weaver brings salt laden barges from Cheshire, and at other points the railways will bring the produce of the excellent coal fields of South Yorkshire and South Lancashire, which will be automatically transferred from the waggons into ocean going steamships.
FIG. 137_b_.—_The English Steam Navvy._ ]
Though the general notion of the construction of the canal as a deep, wide trench, or cutting following the course shown on the map, is sufficiently simple, the operation of carrying this into practice involves the exercise of great skill and ingenuity in dealing with mechanical obstacles. Man’s operations in the world consist but in changing the position of masses of matter; and the properties of matter—its inertia, cohesion, gravitation, etc., are the forces that oppose his efforts. The quantity of matter to be shifted in excavating this trench of thirty-five miles long across the country was no less than sixty millions of tons. The number of “navvies” employed at one time has been 15,000; but even this army of workmen would have made but slow progress with a cutting of this magnitude, had not the “strong shouldered steam” been also called into operation for scooping out the soil. The illustrations (Figs. 137_a_ and #137_b_:fig137b) will show the arrangement of two forms of “steam navvies” that were much used on the works. One (Fig. 137_a_) is similar to the dredgers used for clearing mud out of rivers and canals: it consists of a series of scoops, or buckets, mounted on an endless chain, so as to scrape the material from an inclined embankment and tip it into waggons for removal. The other (Fig. 137_b_) may be compared to a gigantic ladle made to scrape against the face of a cutting in rising, and filling each time its bucket with nearly a ton of the material. It is most interesting to witness the perfect control which the man at the levers exercises over this machine, the movements of which he directs with as much precision as if he were handling a spoon. One of these steam navvies is able to fill 600 waggons or more—that is, to remove 3,000 tons of material—in one day; and as many as eighty of them have been simultaneously used on the Canal works. The value of the plant employed by the contractor is estimated at £700,000, and the length of temporary railway lines (see Fig. 137), for transport of the “spoil,” etc., is said to exceed 200 miles. There is a main line running through from one end of the canal to the other, and known to the workmen as the “Overland Route.” From this diverge numerous branches, some to the bottom of the excavations in progress, others to embankments down which is tipped out the “spoil,” as the dug out material is called; while others connecting with brickfields and quarries, or with existing canals and railway lines, serve to bring supplies of the materials used in the constructions. Some 150 locomotives are constantly at work on these temporary lines, and the coal consumed by them, and by the steam navvies, steam cranes, pumping engines, etc., is equivalent to about two train loads every day.