Engineering Wonders of the World
Volume I

THE ROYAL ALBERT BRIDGE. 35 The Need for a Bridge across the Tamar. As early in the last century as 1844 a railway into Cornwall was proposed, but a line was not constructed till many years after that date. One of the chief reasons for this delay was the necessity of bridging the river Tamar ; for although the expe- dient of a steam-ferry to carry the trains over it was at one time proposed, a bridge ap- peared essential. Several de- signs were prepared, and some of them were objected to by the Admiralty on the ground of possible obstruction to the all-important naval base at Devonport, adjoining the site of the bridge ; but ultimately, in 1852, a scheme was adopted for a structure crossing the river in two main spans, a single pier in the bed of the river offering the least possible inter- ference with the waterway. This involved the construction and erection of two im- mense girders, or trusses, as they are some- times termed, having their ends connected by chains from which the railway was to be sus- pended. It is our desire in describing engineering works to avoid the use of statistics as much as possible, but in the case of large bridges figures are essential to a due ap- preciation of the magnitude of the work. The Royal Albert Bridge has a total length of 2,200 feet. The two main spans over the river are each 455 feet, and the side spans, seven- teen in all, are from 70 feet to 90 feet. The height of the centre pier from its foundation to the top is 240 feet, and the railway is 110 feet above the level of high-water. Like many other engineering marvels, the part most difficult of accomplishment, and, from an engineering point of view, by far the most interesting, is out of sight, and probably little appreciated by those who cross the bridge. Thus one of the chief difficulties was the build- ing of the pier in the centre of the river. Indeed, the task at Saltash was even greater Facts and Figures. The Founda= tions of the Bridge. ISAMBARD KINGDOM BRUNEL, the Designer and Engineer of the Bridge. {Rischgitz Collection.} than in the case of the celebrated Britannia Bridge spanning the Menai Straits, where a rock rose above the surface No such natural facility was afforded in the course of the river Tamar. A depth of 87 feet 6 inches below the water had to be dealt with, and mud and rock débris removed until good foundations were secured. To effect this a specially constructed water- tight cylinder, 95 feet long and 35 feet in diameter, was employed. About 20 feet above the end destined to be lowered into the water a dome was provided, converting it into a diving-bell ; and, lest this should prove un- manageable in deep water, an inner gallery or jacket, 4 feet wide and 20 feet high, was formed round the inner circumference of the cylinder below the dome. This in turn was divided into eleven compartments, into which, by a pneumatic apparatus, air could be