Concrete Culverts, Axecraft, etc.

New Zealand Tablet, Volume LI, Issue 28, 2 July 1924, Page 45

Concrete Culverts, Axecraft, etc.

(Contributed.) Old corrugated iron tanks-which have been discarded on account of their leaky condition, make first-class substitutes for inside boxing for arched, culverts of medium sizes ranging from three to six; feet wide. To illustrate the manner of using them, let us suppose we are about to put in a culvert on a bed of firm claythe size of which measures 3ft Gin in width and 30in in height, and that we have at hand a suitable circular derelict old tank of the required width. Lay down the tank on one side. First find its centre at each end, then with a plumb rule strike a perpendicular line down the centre of both ends, taking care that the tank does not move when passing from one end to the other to strike the second line. From the tops and bottoms of both perpendicular lines next strike lines with a straight edge, along the sides of the tank. Next get an old handsaw, one fairly fine in the teeth, and saw the tank into two halves. The saw will do this job more expeditiously and correctly than other tools.- Cut out one end of each half and place the two halves together, letting one, two, or three of the corrugations overlap at the ends from which the semicircular tops (or bottoms) have been removed, so that it can be correctly seen what length the braces are to be cut, and the exact position for them obtained , for it will be well to brace each half separately by running a 3in x lin along the sawn edges of the tank to prevent them getting out of shape if it (the tank) has to be transported for some distance to the site of the intended culvert. .- In this case I have presumed that at the commencement the tank was not more than 6ft long, and it was necessary to overlap the two halves to get sufficient length, for culverts intended for vehicular traffic should not be shelter than 10ft in length, at least. If a ten-foot tank "eie available of course no overlapping would be necessarv. * ,7- .' ■ * - ' , HOW TO BUILD THE CULVERT. The culvert-bed having been excavated we must now lay down or drive in a. few blocks,on which to rest the tank which serves for inside boxing.; The blocks should nowhere project into the space destined for the concrete. They should be kept 9in above the bottom in this case, the required height of the culvert being 30 inches. (Our tank measured 3ft. Gin in diameter so that, its radius equals 21in.) Any perishable wood will do for the blocks.which will lie no longer necessary when the concrete sets. Box in” the outer sides to enclose concrete ■ for culvert, wings and wheelguards, for it is important that- the whole mass should be joined together in a, solid block. Allow about Min from the edge of .the side of the tank to the inside of the boxing of the sides, in order to give a good base. Eight inches will be thick enough for the concrete at the narrowest place' in the sides. Bring, up the boxing to suit these measurements, the object being to diminish the width of the culvert at the top on economic lines so as to construct it with as little shingle, sand and cement as possible. The materials for making concrete are often costly when- they are not close to the site, whereas earth can generally be got for filling in approaches at little more expense than that of excavating it. 7 ' - (To be continued.)