project, including the ditches, is known as theroadway. The roadbed is the section that includes thesurface course and both shoulders, and the travel wayis the surface course that the vehicle travels on.Slope RatioThe two most common slopes used in roadconstruction are the foreslope and backslope. Theforeslope extends from the outside of the shoulder tothe bottom of the ditch. The backslope extends fromthe top of the cut at the existing grade to the bottom ofthe ditch. The amount of slope in a foreslope orbackslope is the ratio of horizontal distance to verticaldistance (fig. 15-15). That means that for every one(1) foot of vertical (up or down), the horizontaldistance changes proportionally. The following areequations to compute slope ratio:1. If the base and the height are known factors, butnot the slope, use the following:Base ÷ Height = Slope( B + H = S2. If the slope ratio and the height are knownfactors, but not the base, use the following:Slope x Height = Base(S x H = B)3. If the base and the slope ratio are known factors,but not the height, use the following:Base ÷ Slope = Height(B ÷ S = H)Figure 15-15.—Slope ratio.15-12

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