Profile Leveling

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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:A. HighwaysB. CanalsC. SewersD. Water mainsE. SidewalksF. Retaining wallsG. Fences

All of these need accurate information about the topography along the route.

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Characteristics

May be straight segments connected

with curves.

May be multiple segments which change directions with angle points.

May be a single segment.

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Procedure

It is a common practice to use a procedure called stationing.

1. Stations are established at uniform distances along the route.

2. Standard station distance is 100 feet.

3. Half or quarter stations are used when the topography is very

variable.

4. The distance from the starting point to the station is used as the

station identification.

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Procedure-cont.

Intermediate foresights: foresights taken at stations that are not used as benchmarks or turning points.

Intermediate foresights are recorded at each standard station and

at additional stations as needed to define the topography of the

route.

Purpose is to define the topography along the route.

High points

Low points

Changes in slope

Critical points

Roads

Highway

Gutters

Sidewalks

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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?

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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?

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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?

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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.

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Profile Data Table

STA BS HI FS IFS ELEV

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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.

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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.

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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.

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Example One Data Table

STA BS HI FS IFS ELEV

0.0 10.5 110.5 100.00

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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.

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Example One Data Table

STA BS HI FS IFS ELEV

0.0 10.5 110.5 100.0

100 6.3 104.2

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Example One-cont.

The rod reading for each station is recorded on the appropriate line of the table.

STA BS HI FS IFS ELEV

0.0 10.5 110.5 100.0

100 6.3 104.2

200 3.9 106.6

300 4.1 106.4

337.5 7.4 103.1

400 9.2 101.3

489.6 8.0 102.5

Note: the rod reading for station 489.6 is placed in the FS column because this station will be used as a turning point.

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Example One-cont. Step 6: the instrument is moved so the remaining stations can be reached.

STA BS HI FS IFS ELEV0.0 10.5 110.5 100.0

100 6.3 104.2

200 3.9 106.6

300 4.1 106.4

337.5 7.4 103.1

400 9.2 101.3

489.6 6.6 109.1 8.0 102.5

500 6.7 102.5

546.4 6.8 102.2

600 4.9 104.2

700 2.2 106.9

745.1 1.5 107.6

Every time the instrument is moved, a backsight is used to reestablish the instrument height.

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Example One-cont.

The last step is closing the loop.

STA BS HI FS IFS ELEV

0.0 10.5 110.5 100.0

100 6.3 104.2

200 3.9 106.6

300 4.1 106.4

337.5 7.4 103.1

400 9.2 101.3

489.6 6.6 109.1 8.0 102.5

500 6.7 102.5

546.4 6.8 102.2

600 4.9 104.2

700 2.2 106.9

745.1 2.3 109.9 1.5 107.6

TP2 8.3 111.4 6.8 103.1

0.0 11.5 99.9

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Note Check & Allowable ErrorSTA BS HI FS IFS ELEV

0.0 10.5 110.5 100.0

100 6.3 104.2

200 3.9 106.6

300 4.1 106.4

337.5 7.4 103.1

400 9.2 101.3

489.6 6.6 109.1 8.0 102.5

500 6.7 102.5

546.4 6.8 102.2

600 4.9 104.2

700 2.2 106.9

745.1 2.3 109.9 1.5 107.6

TP2 8.3 111.4 6.8 103.1

0.0 11.5 99.9

SUM 27.70 27.80

0.10 = 0.10

€

AE =k M = 1.0 x745.1 2x

5280 =0.5

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Plot of Profile Data

Sidewalk Profile

100.0

104.2

106.4

103.1

101.3

102.5102.3

104.2

106.9

107.6

102.4

106.6

99.5

100.0

100.5

101.0

101.5

102.0

102.5

103.0

103.5

104.0

104.5

105.0

105.5

106.0

106.5

107.0

107.5

108.0

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Distance

Elevation

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:

€

% slope =Rise

Run 100 x =

106.4 - 103.1337.5 - 300.0

100x =3.337.5

100x =8.8 %

This is excessive slope according to ADA standards.

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Excel Calculation of Slope

Station Elevation % slope0.0 100.0

100.0 104.2 4.20200.0 106.6 2.40300.0 106.4 0.20337.5 103.1 8.80400.0 101.3 2.88489.6 102.5 1.34500.0 102.4 0.96546.4 102.3 0.22600.0 104.2 3.54700.0 106.9 2.70745.1 107.6 1.55

It is easy to calculate all of the slopes using a spreadsheet.

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Additional uses of Profile Plot

Profile plots are also very useful for other utility routes such as drain pipes.

Drains are design with a uniform slope.

Plotting the drain on the profile gives a visual reference of the relationship between the earth’s surface and the drain.

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%.

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Drain Plot

96.0

98.0

100.0

102.0

104.0

106.0

108.0

110.0

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Distance

Elevation

Drain

Surface Profile

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

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Drain Plot

96.0

98.0

100.0

102.0

104.0

106.0

108.0

110.0

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Distance

Elevation

Drain

Surface Profile

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.

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What if--cont.• 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.

Drain Plot

96.0

98.0

100.0

102.0

104.0

106.0

108.0

110.0

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750

Distance

Elevation

Drain

Surface Profile

In this example the maximum distance between the surface and the drain occurs at station 200.

€

Depth = 106.6 ft - 98.0 ft = 8.6 ft

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Plots of profile data can be used for many other types of design questions.

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?”.

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.

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How much space will be required for the ditch at the widest point?

The widest point will be at the deepest point.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.Assuming a ditch bottom width of 15 ft and a 2:1 side slope, the ditch at the widest point will be:

The space required is 17.2 ft + 15 ft + 17.2 ft = 49.4 ft

What if--cont.

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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.

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Profile With Side Benchmark

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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.

STA BS HI FS IFS ELEVBM1 8.2 108.2 100.0

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Step 2• Record the first foresight.

• In this example the first foresight (0+00) is an intermediate foresight.

STA BS HI FS IFS ELEVBM1 8.2 108.2 100.0

0.0 9.2 99.0

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Step 3• Add additional intermediate foresights as needed until the first turning point is reached.

STA BS HI FS IFS ELEVBM1 8.2 108.2 100.0

0.0 9.2 99.0

156.5 6.5 101.7

358.6 1.3 106.9

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Step 4• Move the instrument and continue recording foresights.

STA BS HI FS IFS ELEVBM1 8.2 108.2 100.0

0.0 9.2 99.0

156.5 6.5 101.7

358.6 2.1 109.0 1.3 106.9

458.6 5.2 103.8

522.6 7.7 101.3

598.2 5.4 103.6

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Step 5Close the loop

STA BS HI FS IFS ELEVBM1 8.2 108.2 100.0

0.0 9.2 99.0

156.5 6.5 101.7

358.6 2.1 109.0 1.3 106.9

458.6 5.2 103.8

522.6 7.7 101.3

598.2 10.4 114.0 5.4 103.6

BM1 14.0 100.0

Sum 20.7 20.7

0 = 100.0-100.0 0

Note: close to the benchmark not station 0.0.

€

AE =K M =0.1 x598.2 2x

5280=0.047

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Questions?