Culverts are Permanent When Made of Concrete
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.
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.
