The square gauge or guide piles, as they are termed, are usually composed of whole timbers from twelve to fourteen inches scantling, but the plank piles, or sheet-piling, as well as the horizontal ties or wa/inys of half-timbers, being of the same width, but only halt' the thickness of the square piles.
Piles of cast-iron were first employed by Mr. Mathews in the formation of Bridlington harbour, in which work he made use of sheets of iron 8 or 0 feet long by 2 feet in width, and half an inch thick, so contrived at the sides, that each pile should form a dovetail joint with the adjoining one. Mr. Ewart, however, was the first who brought this kind of piling into general notice ; he took out a patent for hls invention in 1822. These piles consisted of plates of iron front 10 to 15 feet in length, 14,1 inches in width, and 11 inch in thickness ; they have a flanch running down the centre, and one at each extremity, turned off at an acute angle with the face. To connect these together, he made use of a smaller pile only inches wide, but having a flanch at each side corresponding with those at the sides of the larger plate, so as to form a dovetail joint with them. Where a greater length of piling was required, a method of lengthening them was adopted, by placing one above another, and securing the horizontal joints by means of dovetail cramps.
Mr. Ewart's piles have been extensively adopted, espe cially by Mr. Ilartley, in the Liverpool docks, who has em ployed them successfully, and speaks favourably of their employment in such works as coffer-darns. Ile states, that considerable care is required in keeping the piles in a vertical position, as they are apt to shrink every blow, and drive slanting. They require to be driven between two heavy balks of timber to keep them in a straight line, as they expose very little section to the blow of the ram, and are so sharp, that they are easily driven out of a right line. There is another very necessary precaution to be taken, which is the keeping the fill] of the ram in the same line as the pile ; otherwise, the ram descending on the pile, and not striking it fairly, all parts equally, the chances arc, that, if in a pretty still stra tum, the head breaks off in shivers, and the pile must be drawn, which is sometimes no easy matter.
Mr. Mylne has also employed those piles to a considerable extent, especially in a large coffer-dam opposite the New River Company's establishment at Broken Wharf, where he succeeded in driving the larger and smaller piles or cramps simultaneously, the usual practice being to drive them sepa rately.
A work on a much larger scale was constructed of the same material by Mr. Cubitt at the sea entrance of the Nor wich and Lowestoft navigation ; but the form of the piles was, in this instance, of a somewhat different description.
The wall consisted exclusively of sheet piling without any guide-piles whatever, each pile being 30 feet long, 18 inches broad, and 1-1- inch thick, having a deep flanch in the centre, without any dovetail or other jointing at the sides; the per fectness of the joints depending entirely upon close and accurate driving. As some assistance to the driving, a pair of strong wrought-iron cheeks, projecting two or three inches beyond the edge of the pile, were riveted on to the lower end, which served as a guide or groove to keep the piles flush. The entire length of wharting thus constructed was about 2,000 feet.
Another work of importance is that of Walker and Bur gess at the Brunswick Wharf, in front of the East India Docks at Blackwall, of which we copy the following descrip tion, as given by Mr. Bo•thwick in the Transactions of the Institution of Civil Engineers.
"The first operation was to dig a trench two yards deep in the intended line, and this was immediately followed by the driving of the timber guide-piles. The deepening in front, which, to give the required depth of 10 feet at low water, mas as much as 12 feet, was not done until near the conclusion of the work ; to have effected it in the first in stance d, without any countervailing advantage except some saving in the driving, have been attended with the double expense of removing the ground firming the original bottom between the old and new lines of \dialling, and after wards refilling the void so left by a material that would re quire time to make it of equal solidity ; and even if' this had been otherwise, such an attempt would have endangered the old wall, or rather would have been fatal to it. The pe•ma nent piling was next begun, the main piles being driven first at intervals of seven ket, and the intermediate spaces or bays then filled in, working always from right to left, towards which the drafts of the sheet-piles were pointed. The ground is a coarse gravel, with a stratum of the hard Ulackwall rock occurring in places, and some triudde was occasionally experienced from its tendency to turn the piles from the proper direction ; but due attention being paid to the form of the points, the drawing was, on the whole, effected pretty regularly, but fe W of the hays requiring closing piles made specially tiu• them, so that the work may be said to be nearly iron and iron (loin end to end ; at the same time, the vertical joints of the piling being all covered. as will be noticed pre sently, any slight imperfection, in this respect, is no serious detriment to the work as a whole.