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ROAD PROFILE The procedure used to plot road profiles is discussed in chapter 7 of the EA3 TRAMAN. From your study of that TRAMAN, you know that a profile is the representation of something in outline. When applied to roads, this means that a profile is a longitudinal-section view of the earth along the centerline, and it is always viewed perpendicular to the centerline.As you know, profile-leveling procedures are used to determine the ground elevations at each of the station points along the center line. These elevations are recorded in the surveyors notebook, which is used by the draftsman to prepare the profile drawing. Generally, the profile is drawn on the bottom portion of plan-and-profile paper, directly below the road plan. An example of a road profile is shown in figure 3-4. A road grade line is also drawn on the lower portion of the plan-and-profile paper and is represented by a heavy solid line, as shown in figure 3-4. Like the profile, the grade line is a longitudinal section taken along the center line and shows the elevations to which the road is built. The grade line is normally the center-line elevations of the finished surface but may be the center-line elevations of the subgrade. If the subgrade was used, make a special note of it. The grade lines are a series of straight lines that are connected, where necessary, by curves (called vertical
Figure 3-4.-Road profile. curves), which will be discussed shortly. The grade lines may be level or sloped. If the lines slope upward, the grade is positive; if downward, the grade is negative. The slopes are in reference to the direction of increasing stations. The amount of slope is lettered above the grade line and is usually indicated as the percent of slope. In figure 3-4, the slope from station 66 + 00 to 71 + 00 is +2.00 percent. This means the center-line grade rises 2 feet in 100 feet horizontal distance. If the slope is -1.50 percent, the grade would fall 1.50 feet in 100 feet horizontal distance.At vertical curves, the straight lines are tangents that intersect at a point called the point of vertical intersection (PVI). This point is comparable to the PI of horizontal curves.Vertical Curves If the road is to offer safe, comfortable driving conditions, the PVI should not break sharply. The length of the curve depends upon the steepness of the intersecting grades. In most cases, a vertical curve is symmetrical in that its length is the same on both sides of the PVI. Unlike the length of a horizontal curve, the length of a vertical curve is the horizontal distance from beginning to end of the curve, rather than the distance along the curve. The station on which the curve begins and ends is called the point of vertical curvature (PVC) and point of vertical tangency (PVT), respectively. Unlike horizontal curves, vertical curves are parabolic; they have no constant radius. Therefore, the curves are plotted, usually in 50-foot lengths, by computing thecurve, or oververtical; one at the bottom of a hill or a dip is called a sag curve, or undervertical.Drawing the Grade Lines You should use the same horizontal and vertical scale to draw the grade line as to draw the profile. Ibis allows the amount of cut or fill for a particular point to be measured. If the grade line is higher than the profile, fill is required; if lower, cut is required. The profile and grade-line drawings also show the relative locations of drainage structures, such as box culverts and pipe. You use only the vertical scale to draw these structures. You can plot the heights of the structures accurately, using the vertical scale. However, because of the exaggerated difference between the vertical and horizontal scales, you cannot draw the width of the structures to scale. Therefore, you should draw the width of the structures just wide enough to indicate the type of structure. You should show a box culvert as a high, narrow rectangle and a round pipe as a high, narrow ellipse. |
 
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