Chap. VI.
FRANCE.
219
Between the rows of piles, and particularly in the front towards the sea, was a filling-in ofclay.
The turning gate revolved upon a pivot, at the end of a middle post; on each side of thispost, and framed into it, were five braces; over the skeleton framing towards the side onwhich the water was retained, it was closely boarded; and had two openings which wereshut by paddles, worked by a rack and pinion. The top of the middle post had a collar,through which it passed, and in which it could turn freely round. This turning gate wasmade two feet more in width than the lock, and shut against a reveal on each side in theside walls, constructed for the purpose. To keep this gate firmly closed, a wedge-shapedpiece of timber work was pressed against it, which was moved by means of a rope attachedat the top. When it was required to open the turning gate, the small paddle was firstremoved, and as the water escaped, the gate was gradually slacked by a cable attachedto a capstan. The tide as it mounted shut the gate again, by mere pressure; thelock-keeper dropped the wedge and closed the paddle, when the water required was ad-mitted.
Sluice of the Canal of Bergues is a good exemplification of the manner in which M.Clement laid the timber foundations, where the soil, as in this case, was a moving sand.
The outline of the platform being set out, piles were driven, from 10 to 12 feet in lengthand about 11 inches square.
Four double rows of piles were driven to carry the binding pieces, morticed at the headof the sheet piling, driven in at the two extremities of the platform; others were placedunder the sills, and a single row at the angles, made by the side and cross walls; theplanking was laid against, and not morticed, as in other instances, into these binding pieces.These ten rows of double and single piles were capped by as many binding pieces ; thepiles were driven at every six feet, and so dispersed, that in the double rows, one cameopposite the intervals of the others. The binding pieces, placed four inches apart,formed a groove or space regulated by the thickness of the planks introduced between them,which were by this means kept in a line. These were also guided at the foot by anotherfixed piece of timber, which prevented their being driven out of place; these pieces weresecured at regular distances by round pins passed through holes made at every six feet, andwere kept in their places by keys passing through their ends. When a sheet pile came incontact with one of these pins, it was taken out, and a hole cut to allow it to pass; whenthe sheet pile was again driven, other square pins were substituted, passing through thesheet pile and its two binding pieces, the rows of which extended throughout the entirewidth of the foundation, and three or four feet beyond the projection of the buttresses, toprevent the current of water from entering the foundation, which is the main use of sheetpiling. Several divisions are necessary in structures of this kind to ensure perfect success.
\\ ith respect to the other piles, as many rows were driven as there were cross timbers ;viz. three between the first and second rows of sheet piling, six between the second andthird, five between the third and fourth, six between the fourth and fifth, and three betweenthe fifth and sixth, these rows being three feet apart from centre to centre. The number ofpiles in each row was encreased according to the nature of the bottom, but they were morefrequent under the wing walls than under the platform, where there were scarcely any,except under the timbers which run lengthwise; sometimes they were omitted, whilstunder the wings and piers, where the lock had several passages through heavy masses ofmasonry, more precautions were taken, and a greater number of piles driven, they havingthe effect of bearing the additional weight, and also serving to consolidate the soil, whichis compressed in a ratio proportionate, inversely, to the reduction of the volume of earth.After the piles were driven, they were cut off about 3 feet 6 inches above the bottomwhere the filling in masonry commenced ; their heads were levelled, except those to whichwere attached the binding pieces, which confined the sheet piling. The head of each pilehad a tenon cut on it, which passed through the mortices of the cross timbers, formed acapping, and were held fast by an iron pin passing through them. The longitudinal andcross timbers were about 30 feet in length, and 12 inches square. When all the piles weredriven and the loose earth taken out between the heads, the spaces were filled with goodmasonry to the depth of about three feet, after which the cross timbers were laid, the underparts of which were filled with mortar and closely bedded. The cross timbers which cameunder the two sills, as well as the masonry, were raised a foot higher above the piles thanthe others, to form that part of the chamber of the sluice against which the gates rested.
r Ihe cross timbers being placed, they formed the first layer, which entered partly into themasonry ; above these was another platform of longitudinal timbers, crossing the others atright angles, and being halved in and well secured at the intersections by irons.
One line of longitudinal timbers was laid under the face of each wall, both back andfront; the others in the intermediate spaces, so that there were four under each wall. Theplatform between the walls was divided into four equal parts, and at each division was laida longitudinal timber, and some short lengths under the counterforts.
" lien the double layer of timber was completed, the voids were filled up with masonry;