Using Profile Data

The results of profile leveling surveys are most useful when they are plotted in a graph. The principal purposes for plotting a profile are: (1) to aid in the selection of the most economical grade, location, and depth of irrigation canals, drainage ditches, drain tile lines, sewer lines, roads, etc.; and (2) to determine the amount of cut or fill required for these installations. The graph is plotted with the elevation on the ordinate (vertical scale) and the stations on the abscissa (horizontal scale).

The use of computer spreadsheets makes it much easier to plot and complete "What if?" examples using surveying data.

Problem: What will be the maximum depth of cut for the data in Table 15.2 to install a drain at 2.0 ft below the elevation of station 0.0 and with a slope of 0.5 %?

Solution: This problem could be answered by calculating the difference in elevation between each station and the proposed drain, but that would require a calculation for almost every station. Plotting the data will provide the visual information to determine where the greatest depth will be, Figure 15.11.

The plot shows that the maximum elevation of the profile is 105.7 ft and at that station the elevation of the drain will be at 98.20 ft.

The maximum depth of cut to install the drain is 7.5 ft. The problem could also be solved by calculating the difference in elevation

V""--105.7 ft

-Drain

—"

X

_—-— 98.20 ft

——- "

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FIGURE 15.11. Profile plot of example data with drain.

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FIGURE 15.11. Profile plot of example data with drain.

between the profile and the drain for each station surveyed using the equation:

Elevationdrain = Elevationstarting + (Station distance x Slope).

With a slope for the drain of 0.5%, for station 290 in the sample data the elevation of the drain is

Elevationdrain = Elevationstarting + (Station distance x Slope) = 96.7 ft + (290 ft x 0.005) = 96.7 ft + 1.45 ft = 99.15 or 98.2 ft.

The elevation of the profile at station 290 (105.7 ft) minus the elevation of the drain at station 290 (98.2 ft) leaves a depth of cut of 105.7 - 98.2 or 7.5 ft.

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