Ontario Sessional Papers, 1906, . andfill all voids between the larger stones. The bridge seat should in design be adapted to the type of Inidgo to beerected, and should be finished with fine concrete. For truss bridges up to75 feet span, there should be a top width of about three feet. The remainderof the abutment, if designed as a retaining wall, may have a thickness downto the footing courses e(iual to f of the depth below grade, the width in-creasing at the back of the abutment, and the face being vertical. A bottom footing, about two feet thick and projecting about twelve inches,
Ontario Sessional Papers, 1906, . andfill all voids between the larger stones. The bridge seat should in design be adapted to the type of Inidgo to beerected, and should be finished with fine concrete. For truss bridges up to75 feet span, there should be a top width of about three feet. The remainderof the abutment, if designed as a retaining wall, may have a thickness downto the footing courses e(iual to f of the depth below grade, the width in-creasing at the back of the abutment, and the face being vertical. A bottom footing, about two feet thick and projecting about twelve inches,should form a base for the abutment. Care should always be taken to com-mence the abutment on a firm, unyielding stratum of earth, but ordinarilythis can be secured by excavating about two feet below the bed of the stream. Wing walls should be built as the situation may require, to protect thel)ridge and embankment from the flow of water. The top width of a wingshould ordinarily be eis-hteen inches or two feet wide, and carried down with. Concrete Arch, near Glen Huron, County.—Span, 35 Feet; Cost. $1,114. a batter at the back to a footing of the same width as the abutment. Byhaving the batter in this way, the earth rests on the abutments, and risesand settles more readily when acted upon by frost. An abutment, in addition to supporting the bridge, must retain or keepin place, the earth filling behind it, so that there is a tendency to push itoutward and overturn it on its footing. The undermining action of thestream has also to be guarded against. As the work is carried upwards, theback filling should be put in place and consolidated. If the earth founda-tion of the abutment is not secure, and unequal settlement or scour of thestream is possible, the bottom should be strengthened with piles driven at 2^feet centres, the tops cut level, and the spaces filled with broken stone. Theheads of the piles should be covered with a timber or concrete platformupon which to buil
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