[PPT6] Profile Leveling

Question 1

PROFILE LEVELING

Answer 1

• Profile leveling is used to establish changes in elevation along a line.
• It provides the needed data or information about the topography along the proposed routes.
• Profile leveling is a method of surveying that has been carried out along the central line of a tract of land on which a linear engineering work is to be constructed/ laid.

Question 2

STAKING AND STATIONING THE REFERENCE LINE

Answer 2

• Depending on the particular project, the reference line may be a single straight segment, as in the case of a short sewer line; a series of connected straight segments which change direction at angle points, as with transmission lines; or straight segments joined by curves, which occur with highways and railroads.
• The required alignment for any proposed facility will normally have been selected as the result of a preliminary design, which is usually based on a study of existing maps and aerial photos.
• The reference alignment will most often be the proposed construction centerline, although frequently offset reference lines are used.
• To stake the proposed reference line, key points such as the starting and ending points and angle points will be set first. Then intermediate stakes will be placed on line, usually at 100-ft intervals if the English system of units is used, but sometimes at closer spacing. If the metric system is used, stakes are usually placed at 10-, 20-, 30-, or 40-m spacing, depending on conditions.
• Distances for staking can be taped, or measured using the electronic distance measuring (EDM) component of a total station instrument operating in its tracking mode.
• Stationing is a system of measurement used for road layout and construction. An arbitrary starting point is designated at the start of the roadway project as the beginning station, and all distances along the roadway centerline are measured from that point.
• If the beginning point was a stake 100 ft along the line from it would be designated the one 200 ft along the line etc. The term full station is applied to each of these points set at 100-ft increments. If the English metric system is used, full stations are 1 km (1000 m) apart.

Question 3

REMINDERS

Answer 3

• Starting point is designated as 0+000.
• Stationing is usually done every 20 meters.
• The number to the left of the + is how many 1 km stations you are from the beginning station and the number to the right of the + is your distance beyond that full station. So the signs 22+015 is 22x1000 + 15 or 22 015 meters from the beginning of the project.
• In rugged terrain and in urban situations, stakes are normally set closer together, for example at half stations (50-ft increments) or even quarter stations(25-ft increments) in the
• English system of units. In the metric system, 20-, 10-, or even 5-m increments may be staked.

Question 4

FIELD PROCEDURES FOR PROFILE LEVELING

Answer 4

Profile leveling consists simply of differential leveling with the addition of intermediate minus sights (foresight) taken at required points along the reference line.
* Whether the stationing is in feet or meters, intermediate sights are usually taken at all full stations.
* Intermediate sights should always be taken on “critical” points such as railroad tracks, highway centerlines, gutters, and drainage ditches.
* In profile leveling, lengths of intermediate minus sights vary, and in general they will not equal the plus sight length.
* Instrument heights (HIs) and elevations of all turning points are computed immediately after each plus sight and minus sight.
* As illustrated, the page check is made by adding the algebraic sum of the column of plus sights and the column of minus sights to the beginning elevation. This should equal the last elevation tabulated on the page for either a turning point or the ending benchmark.

Question 5

DRAWING AND USING THE PROFILE

Answer 5

• Prior to drawing the profile, it is necessary to compute elevations along the reference line from the field notes. However, adjusting the HIs will be done first, because they will affect computed profile elevations.
• After adjusting the HIs, profile elevations are computed by subtracting intermediate minus sights from their corresponding adjusted HIs.
• The profile is then drawn by plotting elevations on the ordinate versus their corresponding stations on the abscissa.
• In drawing profiles, the vertical scale is generally exaggerated with respect to the horizontal scale to make differences in elevation more pronounced.
• The rate of grade (or gradient or percent grade) is the rise or fall in feet per 100 ft, or in meters per 100 m.