Engineering Wonders of the World
Volume I

THE MANCHESTER SHIP CANAL. 159 differ in dimensions, so that they may be used by vessels of varying tonnage. The largest lock is 600 feet long Entrance anj gQ feet . <]ie seconcj( Ship Canal 350 feet by 50 feet; and the third, 150 feet by 30 feet. When the Canal was opened, these locks maintained the water-level at a depth of 26 feet; but the depth over the entire length, as also in the largest dock (No. 9) Depth of af. Manchester, has since been the Canal increased to 28 feet, and the other large docks (Nos. 6, 7, 8) will be deepened to 28 feet before the end of 1909. At each side of the principal lock are culverts 12 feet high and 6 feet wide. These enable it to be filled or lowered with such rapidity that a large ocean-going vessel can pass through in the space of eight minutes, or even less. From Eastham to Runcorn the course of the Canal is along the Cheshire bank of the Mersey. Owing to the irregular character of the coast-line, the engineers Bays to jia(^ cross three bays, and be J crossed eac^ were comPe^ed to erect an embankment dividing the Canal from the estuary. The first of these embankments, 7,000 feet long, is in Pool Hall Bay. A uniform width was preserved at the top of this embankment, but the height ranged from 10 First feet at either end to 40 feet in Embank- J _ , „ ment the centre. Banks of rubble were first formed on the fore- shore at either side of the bay ; and, as the layer of mud in no place exceeded 24 inches in depth, a firm foundation on the hard clay was soon reached. The space between the banks of rubble was filled with hard boulder clay, and, under the influence of tidal action, this material quickly formed a water-tight mass. No difficulty was experienced in making the north and south sections of the same embank- ment ; the foundation of the former for 3,500 feet, and of the latter for 1,000 feet, being stiff boulder clay. But the intermediate portion, 2,500 feet long, caused all sorts of trouble. Mr. Whately . Many Eliot (now Sir Whately Eliot), Dlff,culties- who was in charge of the Eastham division during construction, has described the first of these difficulties, which occurred about two thousand feet from the south end of the embankment, where, at the base of the outer slope, a bank of rubble had to be tipped to support the large quantity of clay that formed the hearting. Here the embankment was 40 feet high, and it had to cross a deep channel scoured by every tide. The rubble bank had been raised to a height of nearly 20 feet, and the space dividing it from the inner rubble bank was ... “slides. filled in with clay, when sud- denly, without the slightest warning, the outer bank slipped forward towards the estuary for a distance of fully 150 feet, and the clay heart- ing followed in its wake. The cause of the “ slide ” was found to be the old bed of a stream which had disappeared, leaving only deep mud behind.