Always check your work by plotting the grade tangents and the curve in profile on an exaggerated vertical scale; that is, with the vertical scale perhaps 10 times the horizontal scale. After the POVCs have been plotted, you should be able to draw a smooth parabolic curve through the points with the help of a ships curve or some other type of irregular curve; if you cant, check your computations.

After you have had some experience computing curves using a table as shown in the foregoing examples, you may wish to eliminate the table and write your computations directly on a working print of the profile. The engineer will set the grades and indicate the length of the vertical curves. You may then scale the PVI elevations and compute the grades if the engineer has not done so. Then, using a calculator, compute the POVT elevations at the selected stations. You can store the computations in some calculators. That allows you access to the grades, the stations, and the elevations stored in the calculator from one end of the profile to the other. You can then check the calculator at each previously set PVI elevation. Write the tangent elevation at each station on the work sheet. Then compute each vertical offset: mentally note the x/ 1 ratio; then square it and multiply by e on your calculator. Write the offset on the work print opposite the tangent elevation. Next, add or subtract the offsets from the tangent elevationsPVC, PVI, PVT, and the e. Figure 11-21 shows a portion of a typical work sheet completed up to the point of drawing the curve.

FIELD STAKEOUT OF VERTICAL CURVES

The stakeout of a vertical curve consists basically of marking the finished elevations in the field to guide the construction personnel. The method of setting a grade stake is the same whether it is on a tangent or on a curve, so a vertical curve introduces no special problem. As indicated before, stakes are sometimes set closer together on a curve than on a tangent. But that will usually have been foreseen, and the plans will show the finished grade elevations at the required stations. If, however, the field conditions do require a stake at an odd plus on a curve, you may compute the needed POVC elevation in the field using the data given on the plans and the computational methods explained in this chapter.

Figure 11-21.Profile work sheet.

Figure 11-22.Compound curve.