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Art of Construction - Earth Roads

road, drainage, underdrainage, water, ground, dry and surface

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ART OF CONSTRUCTION - EARTH ROADS.

Drainage. Drainage is the most important matter to be considered in the construction of earth roads, since no road, whether earth or stone, can long remain good without it. Drainage alone will often change a bad earth road to a good one, while the best stone road may be destroyed by the absence of proper drainage. Water is the natural enemy of earth roads, for mixed with dirt it makes mud, and mud makes bad going The rain or snow softens the earth; the horses' feet and the wagon wheels mix and knead it; and soon the road becomes impassable mud, which the frost finally freezes, the second state of the road being worse than the first—for a time at least. Further, if the water is allowed to course down the middle of the road, it will wash away the earth, and leave gullies in the surface that must be laboriously filled up by traffic or repairs. No road, however well made otherwise, can endure if water collects or remains on it. Prompt and thorough drainage is a vital essential in all road construction, and particularly so for earth roads.

A perfectly drained road will have three systems of drainage. each of which must receive special attention if the best results are to be obtained. This is true whether the trackway be iron, broken stone, gravel, or earth, and it is emphatically true of earth. These three systems are underdrainage, side ditches, and surface drainage.

Underdrainage.

Any soil in which the standing water in the ground comes at any season of the year within 4 or 5 feet of the surface will be benefited by drainage; that is, if the soil does not have a natural underdrainage, it will be improved for road purposes by artificial subsurface drainage. It is the universal observation that roads in low places which are underdrained dry out sooner than undrained roads on high land. Underdrained roads never get as bad as do those not so drained. Underdrainage without grading is better than grading without drainage; and, in general, it may he said that there is no way in which road taxes can be spent to better advantage than in subsurface drainage. Underdrainage is the very best preparation for a gravel or stone road. Gravel or broken stone placed upon an undrained foundation is almost sure to sink (perhaps slowly, but none the less surely), whatever its thickness; whereas a thinner layer upon a drained road-bed will give much better service. Underdrained roads without gravel are better than

graveled roads without underdrainage.

The Object. The opinion is quite general that the sole object of underdrainage is to remove the surface water, but this is only a small part of the advantages of the underdrainage of roads.

The most important object is to lower the water level in the soil. The action of the sun and the breeze will finally dry the surface of the road; but if the foundation is soft and spongy, the wheels will wear ruts and the horses' feet will make depressions between the ruts. The first shower fills these depressions with water, and the road is soon a mass of mud. A good road can not be maintained without a good foundation, and an underdrained soil is a poor foundation, while a dry subsoil can support almost any load.

A second object of underdrainage is to dry the ground quickly after a freeze. When the frost comes out of the ground in spring, the thawing is quite as much from the bottom as from the top. If the land is underdrained, the water when released by thawing from below will be immediately carried away. This is particularly im portant in road drainage, since the foundation will then remain solid and the road itself will not be cut up. Underdrainage will usually prevent the "bottom dropping out" when the frost goes out of the ground.

A third, and sometimes a very important, object of subdrainage is to remove what may be called the underflow. In some places where the ground is comparatively dry when it freezes in the fall, it will be very wet in the spring when the frost comes out—surpris ingly so considering the dryness before freezing. The explanation is that after the ground freezes, water rises slowly in the soil by the hydrostatic pressure of the water in higher places; and if it is not drawn off by underdrainage it saturates the subsoil and rises as the frost goes out, so that the ground which was comparatively dry when it froze is practically saturated when it thaws.

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