A Treatise On The Principles And Practice Of Harbour Engineering

240 HARBOUR ENGINEERING. consist of two parallel jetties which have been built out from the shore-line into the Gulf of Mexico. They are about 6700 feet long, and extend into 24 feet of water, their direction being E.N.E., and they are 1000 feet apart between centre lines. Following the precedent of the work at the mouth of the Mississippi, Dr Corthell, their designer, constructed them of brushwood mattresses consolidated with rubble stone and detritus. The brushwood was obtained locally, either from the adjacent banks of the river, in which case it was conveyed by barges, or from near the railway, when it was transported by waggons provided with side-posts to retain the material, which, of course, though light, was bulky. The railway was specially extended from the town of Tampico to the mouth of the river for the purpose of conveying materials not only to the site, but also to their place of deposit. To this end, a trestle pier was constructed, which carried a double line of rails with several cross- overs. The mattresses were slung from the pier, between the underside of the pile caps and the surface of the water. “For building the mattresses, supports of pine scantling, about 3 inches by 8 inches and of a length equal to the width of the mattress, were suspended athwart the jetty line from the caps and stringers of the pier, by means of ropes so arranged that they could be easily and simultaneously released. On the skids were laid other lines of scantling 3 inches by 6 inches, for about 60 feet, the length of the mattress lying longitudinally with the jetty. In these scantlings, forming the bottom framework of the jetties, there were inserted, before being laid on the skids, irou rods f inch in diameter and of the length required for the thickness for the mattress, which ranged between 4 feet to 7 feet. These longitudinal strips were placed 5 feet apart on the suspended skids, with the rods upright; the brush was then brought to the work, either in a barge alongside when the sea was smooth, or by cars overhead if the sea was rough. It was packed as closely as possible, first in a layer athwart the jetty, and then in a layer lengthwise with the jetty, and so on, until the required thickness was obtained. Mattress strips, or scantlings, of the width of the mattress, were then placed over these rods ; and by means of heavy mallets and powerful “grip” levers, with an iron jaw to take hold of the rod, a pull of 3000 Ibs. was brought to bear, and the mattress was compressed about 20 per cent. The rods were then bent down over the strips to hold them securely.” The character of the brush was not altogether satisfactory ; it was gener- ally crooked and very stiff, and did not yield to compression during construc- tion, or give way to form solid work until it had been heavily loaded a long time with stone under water. For this reason, the final compression after loading was iiearly 50 per cent, of the bulk of the mattress on completion. “ Between six and twelve waggon loads of riprap stone, each car carrying about 12 cubic yards, were then usually hauled by the locomotive to the point over the mattress. The ropes suspending the mattress were released, and the stone from the waggons thrown on to it, causing it to sinit out of sight in a few moments. Mattress work was thus carried on when it would