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How to Build a Sand Clay Road

by Prof. M. Goode Homes, Department of Civil Engineering,
University of South Carolina

When a sand-clay road is built upon a clay sub-grade, proper drainage is one of the most essential things, for unless the sub-grade of the road is dry and firm the surfacing of sand-clay is sure to break through. Ordinarily side ditches, which must be large enough to carry off all of the water falling on the road, will be sufficient. These side ditches should be wide and shallow, rather than narrow and deep, as thus they will not be hard to keep open nor dangerous to travel. They should be from four to five feet wide and from one to one and a half feet deep, sloping three to one on the side next to the road and down to one on the outer side, and they should have outlets as frequently as possible to carry the water entirely away from the road. When the sub-grade is wet or damp most of the time, or is through swampy land, tile sub-drains should be laid in order to keep the foundation of the road dry and firm. It must be borne in mind that greater care must be exercised to keep the clay sub-grade dry and in the majority of cases of a sub-grade in sandy soil.

Preparing Sub-Grade

The roadbed should be graded true to the lines and grades established by the engineer. All spongy material, vegetable matter, trees, roots and stumps should be carefully removed from the roadbed, and the space thus filled in with sound material, and the surface of the roadbed should be dry and the sand and clay should be ploughed and harrowed with a disc harrow to a depth of four inches until the clay is completely pulverized, and the clay sub-grade should be comparatively dry, or it will not pulverize. After this has been done the roadbed should be leveled up, and it will then be ready for the sand.

Mixing Sand and Clay

The sub-grade is now covered with six to eight inches of clean, sharp and sound sand. (When the clay already contains much sand, the amount of sand stated above should be cut down by that much.) The sand should be spread evenly and be of a uniform thickness. To get the best results the roadbed should be dry when the sand is added, and especially should it be dry when the sand and clay are mixed, as it is very difficult to mix the sand evenly with the clay when the latter is wet and sticky. The mixing is now carried on with a spike or spring tooth harrow until the sand and clay are thoroughly incorporated and the mixture is brought to a state of fine sub-division. The roadway is now shaped up with road machine (a split-log drag may be used), the crown being at least one-half inch per foot of half width of the road, and thrown open to traffic. From now until the surface becomes thoroughly consolidated the greatest care should be exercised to keep the surface smooth and properly crowned, and for at least a week the surface of the roadway should be reshaped every morning with the road machine, for if the roadway is worn into ruts at first it is a hard matter to ever get a smooth surface. At first the roadway will get muddy and sticky after each rain, but this is a natural consequence [until the sand and clay] become thoroughly consolidated. If an excess of clay work to the surface and makes the roadway sticky, more sand should be added until the trouble ceases. On the other hand, if the roadway is too sandy, it is best to let it alone, as this trouble will adjust itself.

Sprinkling and Rolling

[If] it is desired to consolidate the surface at once, as soon as the sand and clay are thoroughly mixed, the roadway should be sprinkled and harrowed until the sand and clay are worked into a mud of homogeneous consistency. As soon as it has dried out sufficiently, the surface should be smoothed with the road machine and given the proper crown. And just before it becomes entirely dry it should be rolled until it becomes hard and ceases to show the tracks of ordinary loaded vehicles. The roller should weigh from six to ten tons, never more, and may be either horse power or a steam roller.


The maintenance of the sand-clay road is exceedingly simple and easy, if properly and consistently attended to. The surface should be kept smooth and even, and free from all holes and depressions, and ruts and transverse drains. It is imperative to prevent well defined water courses, even they be small, from forming in the sand-clay surface; for the sand-clay mixture is peculiarly subject to the destructive action of running water. After each rain, or at least once every month immediately after a rain, the surface of the road should be dragged with a split-log drag or some similar device until the surface is smooth and the crown restored. When the surface becomes very rough or badly worn it is best to plough it up and pulverize the material with a harrow, after which the surface is reshaped and consolidated as in the case of a new road. Whenever the surface becomes very rough or badly worn it is best to plough it up and pulverize the material with a harrow, after which the surface is reshaped and consolidated as in the case of a new road. Whenever the sand-clay has worn too thin, new surfacing material should be added before the roadway is ploughed and harrowed; as otherwise the old and new material will not mix or stick together, and the new surfacing will scale off and soon be wasted.

The side ditches should be given a general cleaning and repaired at least once in the early spring and once in the early fall. All trash and other obstructions should be thrown out on the sides opposite from the roadway; and all scoured places and holes in the ditches should be filled up with firmly packed rock and clay. Especial care should be taken to see that all outlets are open and ample to take all of the water entirely away from the vicinity of the road. The shoulders that form between the roadway and the side ditches should be removed so that all water falling on the surface of the road can at once flow into the side ditches.

Updated: 11/18/2015
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