The construction of roads and airfields, or portionsof roads and airfields, is often tasked to the Seabees for accomplishment. As an Engineering Aid, you can expect involvement in projects of this type. This involvement may include assisting the engineering officer in the design of these facilities or in the surveying operations required before, or during, construction. Whatever your involvement is, you must be familiar with the terminology, methods, and materials of road and airfield construction. This chapter will provide that familiarity.
A military road is defined as any route used by the military for transportation of any type. This includes everything from a superhighway to a simple path through the jungle. The type of road required depends mainly upon the missions of the units that use it. In forward combat zones, the requirements are usually met by the most expedient road; that is, one that will get the job done with no attempt for permanency. In the rear zones, however, the requirements usually call for somedegree of permanency and relatively high construction standards.
When assigned to the engineering division, you may help prepare the working plans for the construction of roads and airfields; for example, a two-lane, earth, gravel, or paved-surface road. Figures 3-1 and 3-2 show the basic parts of a road. The following paragraphs give
Figure 3-1.-Perspective of road showing road nomenclature.
Figure 3-2.—Typical cross section showing road nomenclature.
definitions of some terms that you are likely to use whenpreparing the working plans for a road:
1. CUT. Has two connotations: (1) an excavationthrough which the road passes and (2) the vertical distance the final grade is below the existing grade.
2.FINAL, OR FINISHED, GRADE. The elevation to which the road surface is built.
3.SURFACE. That portion of the road that comes into direct contact with traffic.
4.EXISTING GRADE. The undisturbed earth before construction begins.
5.FILL. Has two connotations: (1) earth that has been piled up to make the road and (2) the vertical distance the final grade is above the existing grade.
6.SUBGRADE. The foundation of a road which can be either undisturbed earth (for a cut) or material placed on top of the existing grade.
7.BASE. Select material (crushed stone, gravel, etc.) placed in a layer over the subgrade for the purpose of distributing the load to the subgrade.
8.TRAFFIC LANE. That portion of the road surface over which a single line of traffic traveling in the same direction will pass.
9.TRAVELED WAY. That portion of the roadway upon which all vehicles travel (both lanes for a two-lane road).
10.SHOULDERS. The additional width immediate y adjacent to each side of the traveled way.
11.ROADBED. The entire width (including the traveled way and the shoulders) upon which a vehicle may stand or travel.
12. ROADWAY. The entire width that lies within the limits of earthwork construction.
13. ROADWAY DITCH. The excavation, or channel, adjacent and parallel to the roadbed.
14. DITCH SLOPE. The slope that extends from the outside edge of the shoulder to the bottom of the ditch. (Sometimes called front slope or side slope.)
15.BACK SLOPE. The slope from the top of the cut to the bottom of the ditch (Sometimes called cut slope.)
16.FILL SLOPE. The slope from the outside edge of the shoulder to the toe of the fill. (Also, sometimes called front slope or side slope.)
17.TOE OF SLOPE. The extremity of the fill (where the existing grade intercepts the fill).
18.INTERCEPTOR DITCH. A ditch cut to intercept the water table or any subsurface drainage. Also, a ditch cut along the top of fills to intercept surface drainage.
19.WIDTH OF CLEARED AREA. The width of the entire area that is cleared for the roadway.
20.SLOPE RATIO. A measure of the relative steepness of the slope, expressed as the ratio of the horizontal distance to the vertical distance.
21.CENTER LINE. The exact center, or middle, of the roadbed.
22.BLANKET COURSE. A 1- or 2-inch layer of sand or screening spread upon the subgrade to prevent mixing of base and subgrade.
23.CROWN. The difference in elevation between the center line and the edge of the traveled way.
24.SUPERELEVATION. The difference in elevation between the outside and inside edge of the traveled way in a horizontal curve.
25.STATION. A horizontal distance generally measured in intervals of 100 feet along the centerline.
26.STATION NUMBER. The total distance from the beginning of construction to a particular point (for example, 4 +58 is equal to 458 feet)