Photos, Hill]
HOW THE REINFORCED CONCRETE ARCHES WERE BUILT WITHIN WOODEN MOULDS
BUILDING THE “OVER-SEA” RAILWAY
The completed track has a somewhat novel appearance. There is the ridge of earth, flanked on either side by a broad ditch, cut by the dredgers and running as equidistantly from one another as if drawn with a parallel ruler. These side canals, however, serve to drain the permanent way to a certain extent.
When the railway-builders made their way through this inhospitable region they did not meet a vestige of civilisation for over 30 miles. Then they came across pathetic evidences of attempts at reclamation here and there in the form of tumbling homes and isolated parties of half-starved negroes, vainly endeavouring to extract some sort of subsistence from the bog.
But it is when the railway emerges from the Everglades that the most wonderful part of the undertaking is seen. A chain of some 30 verdant islands, composed of coral limestone, stretches out in a graceful curve for about 109 miles, to disappear finally into the depths of the Gulf of Mexico at Key West. These reefs are separated by channels of open sea, of varying widths. These interruptions to the continuity of dry land are spanned by massive arched viaducts wrought in masonry. Where the line traverses the islands themselves the permanent way either is carried on embankments or through deep cuts. The expensive bridging has been reduced to the minimum, however, for in some cases where the water is shallow the islands are linked together by a massive solid earthen embankment.
This section of the railway may be said to be amphibious in the full sense of the word. In fact, at one point the passenger in the train is carried beyond the sight of land. The engineer had to build his structure sufficiently strong and solid as to combat the forces of wind and wave, and at a level beyond the reach of the spray. When it is remembered that the railway runs through a territory where tropical storms of terrific fury prevail, and where cyclones are continually wreaking widespread damage, some idea of the character of the work requisite to withstand the buffetings of these abnormal visitations may be gathered.
These climatic disadvantages were brought forcibly before the moving spirit in the enterprise at the time of its conception, and accordingly he demanded that the bridge-work should be built as strongly as engineering science could make it. No expense was to be spared, for the financier was determined that no apprehensions as to safety should be permitted to lurk in the mind of the timid traveller.
The engineer took him at his word. The depth of water in which the viaducts are built ranges from 10 to 15 feet and more, while the rails are laid 31 feet above low water. At some places the channel is wide enough to float a large steamship. The viaducts have been carried out in ferro-concrete, wherein the masonry is strengthened by means of iron rods, freely intersecting, which serve to bind the whole mass into a solid, homogeneous whole, so that the viaduct from end to end becomes practically a single, monolithic structure.
To enable the subaqueous portions of the piers to be built, coffer-dams were erected around the sites, the space within being emptied and kept clear of water by means of powerful pumps. By this means the workmen were enabled to carry out their task of securing the fabric to the solid rock on the dry coral sea-bed. Where the water ran up to a depth of 30 feet, and the situation was exposed to the full fury of gales and of the Atlantic, caissons were sunk for the purpose of constructing the piers to above water-level, the men working in compressed air. The material for constructional purposes was prepared on large, well-equipped floating plants anchored near by. The timber moulds to form the shape of the arches were fashioned and bolted together on dry land, and towed out to sea by tugs to the point of erection and there set in position.