Profile Leveling

1. Profile Leveling

2. Definition A surveying method that yields elevations at definite points along a reference line. Profile leveling establishes a side view or cross sectional view of the earth’s surface • Primary use is for utilities: • Highways • Canals • Sewers • Water mains • Sidewalks • Retaining walls • Fences All of these need accurate information about the topography along the route.

3. Characteristics May be a single segment. May be multiple segments which change directions with angle points. May be straight segments connected with curves.

4. Procedure • It is a common practice to use a procedure called stationing. • Stations are established at uniform distances along the route. • Standard station distance is 100 feet. • Half or quarter stations are used when the topography is very variable. • The distance from the starting point to the station is used as the station identification.

5. Procedure-cont. Intermediate foresights are recorded at each standard station and at additional stations as needed to define the topography of the route. Intermediate foresights: foresights taken at stations that are not used as benchmarks or turning points. • Purpose is to define the topography along the route. • High points • Low points • Changes in slope • Critical points Roads Highway Gutters Sidewalks

6. Defining an Object • Because profile leveling is used to measure the cross section of and the location of objects along a route, one important issue is determining how many stations are required to define the object. • The answer is, it depends on the object and the use of the data. • For example: how many stations would be required to define the cross section of a standard trapezoidal ditch? 6

7. Defining an Object-Ditch --cont • A ditch may have been a trapezoid when constructed, but over time it will change its shape. • What is the effect on the number of stations if a channel has developed in the bottom of the ditch? 7

8. Defining An Object-Street • Another common object is a street. • The number of stations required to define the cross section of a street depends on the required information. • Do you need to know the height of the curb? • Do you need to know the width of the curb? 7

9. Turning Points-cont. When distances to foresights become too long or when the terrain obstructs the view of the instrument, turning points are established. Foresights on turning points and benchmarks are true foresights. Profile leveling is differential leveling with the addition of intermediate foresights.

10. Profile Data Table

11. Example One Determine the profile for a proposed sidewalk that connects two existing sidewalks and bisects a road. Step one: establish the standard stations. Note: the last station (745.1) is established even though it is not a standard station.

12. Example One-cont. Step 2: Determine the sites for the critical features. In this example, the critical features are the rapid change is slope at 337.5 and the road at 489.6. Note a stations were established at 489.6 and 546.4 to define the width of the road and any changes in elevation across the road.

13. Example 1-cont. Step 3: Set up the instrument and start recording data. The first rod reading is a backsight on the first sidewalk (benchmark) to establish the height of the instrument. Note: in this case the true elevation of the benchmark is unknown, therefore 100.00 feet is used.

14. Example One Data Table

15. Example One-cont. Step 4: Start recording the rod readings for each station. Note: station 100 is not used as a benchmark or as a turning point, therefore it is an intermediate foresight.

16. Example One Data Table

17. Example One-cont. The rod reading for each station is recorded on the appropriate line of the table. Note: the rod reading for station 489.6 is placed in the FS column because this station will be used as a turning point.

18. Example One-cont. Every time the instrument is moved, a backsight is used to reestablish the instrument height. Step 6: the instrument is moved so the remaining stations can be reached.

19. Example One-cont. The last step is closing the loop.

20. Note Check & Allowable Error

21. This is excessive slope according to ADA standards. Plot of Profile Data Potting the data helps answer questions such as, “Will the slope of the sidewalk be acceptable?”. In this example the steepest slope appears to be between stations 300 and 327.5. The slope at this point is:

22. Excel Calculation of Slope It is easy to calculate all of the slopes using a spreadsheet.

23. Additional uses of Profile Plot Plotting the drain on the profile gives a visual reference of the relationship between the earth’s surface and the drain. Profile plots are also very useful for other utility routes such as drain pipes. Drains are design with a uniform slope. Assume the survey was completed for a drain pipe instead of a sidewalk. Also assume the starting elevation of the drain pipe is at three feet below the surface at station 0.0 and that the desired slope is 1%.

24. It should be oblivious that this design has problems because at station 550 the drain pipe is above ground.

25. One of the advantages of spread sheets is doing “What if” scenarios. What if the drain slope was changed to 0.5%? The way this spread sheet was set up changing the % slope required changing one value. If the drain pipe will function correctly at 0.5% slope, this would be a workable alternative.

26. What if--cont. In this example the maximum distance between the surface and the drain occurs at station 200. • If the purpose of the survey was for a drain, then additional questions such as, What is the maximum depth of cut? Can be determined.

27. What if the profile survey was for an open ditch? In this situation questions like, “What is the maximum depth of the ditch can be determined?”. Plots of profile data can be used for many other types of design questions. The top width of a ditch is determined by the depth, side slope and bottom width. Cross section profiles can be determined using this data and the profile.

28. What if--cont. The answer to this question is determined by the ditch design. Most drainage ditches have a trapezoidal cross section shape. The bottom width is determined by the anticipated flow rate through the ditch. The side slopes are usually either 2:1 or 3:1 ratio. How much space will be required for the ditch at the widest point? The widest point will be at the deepest point. Assuming a ditch bottom width of 15 ft and a 2:1 side slope: The ditch at the widest point will be: 17.2 ft + 15 ft + 17.2 ft = 49.4 ft

29. Example 2 • In the first example the existing sidewalks were used as benchmarks because they were part of the finished design. • When there are no existing structures that can be used for a benchmark, or when all of the existing structures will be removed during construction, a benchmark must be established out side of the construction zone. • In this situation, the notes are started different.

30. Profile With Offset Benchmark

31. Step 1 • The principles are the same. • The difference is that in this case the BS is taken on the benchmark not the first station. The notes use the same column--they just start with the BM instead of 0.0.

32. Step 2 • Record the first foresight. • In this example the first foresight (0.0) is an intermediate foresight.

33. Step 3 Establish additional intermediate foresights as needed until the first turning point is reached.

34. Step 4 Move the instrument and continue recording foresights as needed to complete the profile.

35. Note: close to the benchmark not station 0.0. Step 5 Close the loop

36. Questions?