Chap. VIII.
44 7
well fitted and secured to the piles as before described ; the whole of the piles arc to hestraightened and planed on the edges, and shod with good wrought-iron shoes, and properly
Fig. 449. FRAMING OP THE TIMBERS OP COFFERDAM.
headed and hooped with strong wrought-iron hoops of the same weight as before described,so as to prevent the piles from splitting whilst driving. There will be required four pierdams.
“ Foundations _The earth for the foundations of the abutments is to be excavated to
such a depth, that the tops of the platforms at the front shall not be less than 34 feet6 inches below high water mark, according to the Trinity House standard, and at the back.25 feet below the said Trinity House high water mark, and as shown in the drawings.
“ The earth for the foundations of the two side piers is to be excavated to such a depth,that the tops of the platforms shall not be less than 40 feet below the said Trinity Househigh water mark.
“ The earth for the foundations of the middle piers is to be excavated to such a depththat the tops of the platforms shall not be less than 43 feet below the said Trinity Househigh water mark. When the earth has been excavated to the required depth, piles are tobe driven to sustain the weight of the superstructure; these are to be of elm, fir, or beechtimber, not less, on an average, than 12 inches diameter in the middle, and 20 feet long,properly shod with good wrought-iron shoes, not less than 35 pounds weight each, andgood wrought-iron hoops 30 pounds weight each, so as to prevent the piles from splittingwhilst driving. The piles under the foundations of the abutments are to be driven at rightangles to the inclination of the foundations, and those for the piers are to be driven perpen-dicular, as shown in the drawings; all these piles are to be driven not less than 18 feetbelow the under side of the respective platforms of the piers and abutments, that is, thesquare parts of the piles, besides the shoes are to be driven to this depth. The piles are tobe driven in rows about 4 feet asunder from centre to centre, as shown in the drawings.When all the piles are driven to the requisite depth, their heads are to be cut off level andeven, and the earth from between is to be excavated to the depth of 9 inches below the pile-beads, and the spaces between are to be filled with Kentish ragstone, well beat down andracked in with sharp gravel and lime screenings to the level of the pile-heads, in the pro-portion of one part of lime to five parts of gravel, after which sills of beech, elm, or firtimber, not less than 12 inches square each, are to be laid and fitted solidly on the pile-heads, in the transverse direction of the foundations, and firmly spiked to each pile withjagged wrought-iron spikes 18 inches long, and 1| inches square; between these sills,except at the extremities, which are to be filled with square blocks of stone, the spaces areto be built up with good sound brickwork, composed of the best sound, hard, well-burntgrey stock bricks, set in mortar, composed of four parts of clean sharp river sand to onepart of well-burnt Merstham, Dorking , or other lime equally good ; above these sills thereare to be laid and properly fitted other rows of sills longitudinally over the pile-heads below,