Engineering Wonders of the World
Volume I

164 ENGINEERING WONDERS OF THE WORLD. An Early Bridge Proposal. river had been brought under consideration from time to time. As early as 1839 Charles Eilet, an engineer whose genius was somewhat in advance of his times, designed a sus- pension bridge of three spans, and 900 feet respectively, to of 900, 1,200, be carried on piers built upon foundations of piles. The startling boldness of this scheme was too much, for the authorities, who gladly dismissed it on the score of expense. Later, plans for a suspension bridge of one 1,500 feet span, similar to that across Niagara, and for a tubular bridge, also failed to obtain finan- cial support. Meanwhile engineering science was advan- cing, and Eads was persistently studying the habits of the river, and particularly, by means of a diving-bell, the nature of its bed. The conclusions he was able to arrive at are, their practical bearing upon “ Ice Gorges. apart from bridge-making, interesting enough in their physical explanation to be set forth some- what fully. The Mississippi, where the cur- rent permits, is frozen over in winter, and enormous quantities of floating ice come down to St. Louis from the colder northern regions of the river basin. A sand-bank or a sunken wreck, serving to hold up the flow, may start a “ jam ” reaching from bank to bank. Such an accumulation, called an “ ice gorge,” quickly becomes, under the influence of frost, a solid mass 20 feet thick, constantly increas- ing its size and damming back the water for miles up-stream. The current, sweeping small blocks beneath the obstacle, adds to its thick- ness from below ; and the water, subjected to an enormous and increasing pressure, scours its way through the gravel and boulders down to, and, in the course of the ages, deep into, the rocky strata of the bed. Eventually pres- sure overcomes resistance, and the accumula- tion breaks away, often with disastrous conse- quences in the lower reaches. These “ gorges” generally occur where the breadth of the river is contracted, as at St. Louis, and put an absolute stop to traffic of all kinds, often for a week or ten days at a time. What would have been the fate of Ellet’s bridge, had his otherwise feasible design been carried out, when once the scour got to work on his pile-borne foundations, it is easy to imagine. To Physical , „ Difficulties. stand any chance or proving permanent, it was clear that a pier must be carried right down to bed-rock, and although such an operation was not perhaps beyond th© power of contemporary engineers, the cost of repeating it often enough to carry the short spans of those days across the wide river would have proved quite prohibitive. Added to this was the necessity for considerable height above water-level throughout the length of a bridge to accommodate the important steam- boat traffic ; for a rise of thirty feet in flood is very usual, and, owing to shifting sand-banks, the navigation channel is continually changing its course. Such were the difficulties confronting the engineer when, in 1867—the approach of the railways now promising commercial success— Eads presented his plans to the ,, .. 3 n ax t • i Eads’s Plans, recently-formed St. Louis and Illinois Bridge Company,” an enterprise in the promotion of which he had taken a prominent part. Prompt approval met his proposals. Application for charters was made to the Legis- latures of Missouri and Illinois, a substantial capital was raised, and Eads was appointed chief engineer. Instantly rival concerns sprang into existence, eager to share in what was ob- viously a very valuable concession. Vested interests made their opposition felt, and the Company made little headway. However, work was begun on the west bank, in spite of the fact that another group of charter- holders, calling themselves the “ Illinois and St. Louis Bridge Company ” (observe the in- version of title) had actually commenced