The secret of good roads is good drainage. Standing water soaks into
the road bed, softens the road surface and causes ruts. To keep well
made roads in first-class condition, get the water to the highway drain
tile as fast as it falls. This can be accomplished only by means of
culverts.
The perfect culvert is one which does not rot or rust out, which does
not crush down and clog up the opening, which lasts forever. Concrete
is the only material which fills the bill.
The best time to build a culvert is in the dry months of summer. They
can be shaped either round or square and of a size depending on the
amount of water which must be removed quickly. Usually openings 12 to
18 inches are large enough. Set the culvert as deep in the road bed as
possible, but do not place the outlet end lower than the bottom of the
ditch into which the culvert drains. To keep the culvert well beneath
the road bed, if necessary, make the side ditch deeper at the inlet
end. Determine the grade line of the finished culvert bottom. Only a
little slope is needed. Dig the trench 6 inches deeper than the grade
line and as wide and long as necessary. The width of the trench depends
upon the size of the culvert to be built, and its length upon the width
of roadway under which the water is to be carried. The concrete walls
are each 6 inches thick, so the width of the trench will be 1 foot
greater than the clear width of the culvert. Fill this trench with
concrete mixed 1: 2½: 5, and, while it is still wet place in the
center of it a U-shaped box, turned upside down, of 1-inch boards, the
outside of which is the size of the culvert desired. Fill concrete into
the space between the sides of the box and the sides of the trench and
tamp concrete over the top to a depth of 8 inches. Road culverts should
not be less than 18 inches below the surface of the roadway.
To prevent the material of which the road is made from washing down into
the culvert, small wing or retaining walls must be built at each end.
To do this dig an 8-inch trench 3 feet deep, at each end of the culvert
along the end of the culvert barrel. Frame a form, the width and height
necessary, against the end of the box or pipe. Make another form, of
the same size, but U-shaped, with the opening just large enough to
fit over the outside of the concrete culvert barrel. Set this form 8
inches inside the first. Plumb both forms and brace them securely. Nail
boards across the ends of these two forms and fill them with concrete.
For one week shut off the traffic from passing over the culvert. Allow
the forms to remain in place for two weeks. Replace the road material
over the culvert and keep the ruts carefully filled until the fill has
become solid. Since there are usually many culverts to be built, it is
cheaper to use a collapsible form, adjustable to several sized culverts.
[Illustration]
The box culvert shown in the illustration on page 108 has an opening 18
inches wide and 16 inches deep. The length is 20 feet. The retaining
walls are 8 inches thick, 2 feet high (from the barrel opening), and
do not extend beyond the culvert walls. The bottom and the side walls
are 6 inches thick; the top, 8 inches. Three men, with a highway
commissioner as superintendent, built this culvert in two days.
=Materials Required=
Crushed rock or screened gravel 3 cubic yards at $1.10 $3.30
Sand 1½ cubic yards at $1.00 1.50
Portland cement 4 barrels at $2.50 10.00
------
$14.80
Concrete bridges last forever. With all the bridges and culverts of
concrete, tax officials will no longer need to levy bridge taxes.
[Illustration]