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drafted round the bed and end joints, and the rest of the face to be neatly dressed with a pick point. The bed and end joints to be truly wrought.
“ The coping of the wing walls to be continued through the abutment, so as to prevent the boats striking the face of the wall.
“ The wing walls are to have a curved batter on the face, of one and a half inches to the foot. They are to be vertical behind, with two six-inch onsets, the lowest two feet above the springing of the arch, and the upper one six inches above the crown of the arch, so that the inner line of the foundation will be one foot nearer the centre of the bridge than the inside of the parapet.
“ The water wing walls are each to be forty feet long from the face of the arch; to be two feet thick at top, and three feet at bottom; each to splay back so as to cut into the land at top bank level, and to have a gradually increasing batter on their faces, so as to be not less than four inches to a foot at their extremities.”
Specification for the Bridge built on the Coventry
New Road, Plate IV. fig. 2.
“ The ground where the bridge is to be erected is to be excavated ten feet deep, for the purpose of laying a foundation of timber for the abutments and wing walls.
“ In the space thus opened, 102 piles are to be driven ; they are to be six feet long : sixty-six of them, which are to be under the abutments, are to
be nine and six inches; the remaining thirty-six, which are under the wing walls, are to be six inches square; they are to have a shoeing of three eighths of an inch iron, nine inches long, and two inches broad. The
The upper end of the piles are to be cut into a tenon to be inserted in the sills.
“ The sills are to be twelve inches by nine inches, to be laid perfectly level, and their upper surface eight feet four inches below the ground line: the spaces round the pile heads and between the sills are to be firmly packed with rubble stone and grouted. A four-inch sheeting of good elm or battens is to be laid over the sills, to be thirtythree feet long, seven and a half feet broad for the abutments, and five and a half by eight and a half for each wing wall; it is to be laid close, evenly bedded, and spiked to the sills. The upper surface is to be eight feet below the ground line. On this platform the abutments are to be built of stone masonry in level beds and grouted; they are to be seven feet thick at the foundation, and diminishing by two offsets of six inches each to six feet at the springing, which is to be at eight feet above the top of the platform : they are to be faced nine inches thick with blue metal bricks laid header and stretcher in clean joints. The wing walls are also to be of stone masonry, to be six feet thick at the platform next the abutments, and diminishing to five feet three inches at eight feet from the abutments; this thickness is to be continued to the height of five feet three inches, where their length is increased eight feet nine inches ; at this height
there is to be an offset of one foot, and the work brought up from this to the ground line four feet three inches thick.
“ The arch is to be thirty feet span, rising ten feet; to be built of the best blue brick that can be procured; it is to be one foot ten inches and a half thick at the springing, and to continue of the same thickness from nine feet from the springing, where there is to be an offset of four inches and a half; from thence to the crown it is to be eighteen inches thick; the headers of the arch to show only eighteen inches all round. The arch is to be turned on a centre, constructed of good timber, to be approved of by the engineer.
“ The backing of the arch is to be of good stone masonry three feet six inches at the springing; at the height of two feet above the top of the abutment, there is to be an offset of one foot; at the height of four feet, there is another of a foot; and at the height of five feet to slope to the back of the arch. The water wing walls are to be ten feet long; they are to be founded at the depth of eight feet below the ground line, and to be built of stone masonry two feet thick at the bottom, and diminishing by an offset of six inches at the height of three feet, and to continue of that thickness to the top; they are to rise to the ground line, and to be coped with sod; the splay to be three feet in each, or to be thirty-six feet in the clear at the extremities.
“ The spandrell and wing walls above the ground line are to be of blue brick masonry, to be three feet thick, with nine-inch counterforts, founded on the stone masonry before described ; at the height of five feet, there is to be an offset of three inches, and the remaining thickness of two feet nine inches to be continued to the road line at this height. There is to be a string course of white freestone, six inches thick, one foot on the bed, and projecting two inches over the face of the work; the under edge to be one foot six inches above the upper line of the arch at the crown: a parapet wall is to be built on each wing wall, and over the arch, of fourteen inches blue brick work, three feet six inches in height, and coped with stone three feet in length, six inches thick in the centre, and four inches and a half at the sides, which are to be flush with the brick work.
“ The stones are to be well bedded and jointed with four-inched cast-iron dowels, and the joints run with cement. The whole of the works and materials are to be approved of by the engineer. The mortar to be made use of is to be composed of three parts of sand to one of the best Newbold lime, to be properly worked and used while fresh. All the face work to be laid in mortar composed of two parts of Newbold lime to one of sharp clean sand.”
Where the natural surface of a country is very rugged and precipitous, it will frequently be necessary to build retaining walls.
The following is a specification for building a
retaining wall on part of the Holyhead Road, in North Wales (Plate IV. fig. 3.):
“On sloping ground there must be a retaining wall along the upper side of the road eighteen inches wide at top; its foundation to be laid at least four inches below the bottom of the side drains, and is to be carried up, so as to intersect the slope of the bank, when falling at the rate of two horizontal to one perpendicular; and the slope is to be formed in this manner for at least one yard from the back of the wall by means of swarded turf or stone pavement. The face is to have a curved batter at the rate of one inch and a half in every foot from the top: the back may be in the shape of a rough dyke wall; but every one of the back stones are to be regularly connected with the body of the wall, and not to depend upon the earth behind them."
If a retaining wall be built of brick, the thickness at top should be one brick, or nine inches, and it should increase in breadth by onsets of half a brick at every eight courses to the level of the road, below which the thickness for the stepping of the foundation should increase half a brick at every four courses to the bottom. All the walls of this description should batter in a curve line on the face at the rate of one inch in every foot.
These walls are necessary for supporting earth or other materials used for forming a road; they