SURVEYING 1 CE 215 CHAPTER -3- LEVEL AND · PDF file · 2017-10-07SURVEYING 1 CE 215 CHAPTER -3- ... levelling is called change point. 7. Fore sight ... A change plate should be used

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Ishik University / Sulaimani

Civil Engineering Department

SURVEYING 1

CE 215

CHAPTER -3-

LEVEL AND LEVELING

Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed

2 Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed

CHAPTER -3-

LEVEL AND LEVELING

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CONTENTS

1. Level instrument

2. Bubble

3. Tripod

4. Leveling staff

5. Definitions

6. Reading a staff

7. Finding the target

8. Basic rules for leveling

9. Field notes

10. Procedure of leveling

11. Leveling errors

12. Types of leveling

Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed

1. Level instrument

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1. Base Plate

2. Horizontal Circle

3. Eyepiece

4. Circular Bubble

5. Sighting Pointer

6. Objective Lens

7. Focusing Knob

8. Fine Motion Drive

9. Footscrew

10. Bubble Mirror

Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed 5

Level instrument


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Leveling of the instrument is done to make the vertical axis of the

instrument truly vertical. It is achieved by carrying out the

following steps:

Step 1: The level tube is brought parallel to any two of the foot screws,

by rotating the upper part of the instrument.

Step 2: The bubble is brought to the centre of the level tube by rotating

both the foot screws either inward or outward. (The bubble moves in

the same direction as the left thumb.)

Step 3: The level tube is then brought over the third foot screw again

by rotating the upper part of the instrument.

Step 4: The bubble is then again brought to the centre of the level tube

by rotating the third foot screw either inward or outward.

Level Instrument

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Level Instrument

2. Bubble

When bubble is centred the instrument’s standing

axis is approximately vertical. The compensators in

the instrument take over and adjust the optical

Line of Collimation so that it is horizontal

(hopefully). Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed

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• Keep the pole upright

– Any tilt will disturb your readings


3. Tripod

• Wooden design or aluminum

– From “easy to sit” to “ops, this is high”


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• Tripod stand :- is a portable three-legged frame, used as a

platform for supporting the weight and maintaining the

stability of some other object.

TRIPOD STAND


4. Leveling staff

• Leveling Staff :-Is a wooden or metal ruler one side

runway to meters and centimeters. And is a ruler of solid

wood 2 , 3 , 4 , 5 meters in length and usually 4 meters.


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5. Definitions

1. Datum line (M.S.L.) :- Is the level (line), which are

attributed to it points levels on the surface of the Earth.

Which is the average sea level.

2. Reduced level (R.L) :- Is the high point from datum line.

3. Benchmark (B.M.) :- Are fixed points information site and

attributed placed in different places until you start racing

them when conducting settlement.

4. Back sight (B.S.) :- Is the first reading taken after placing

the device in any position so that we see the greatest possible

number of points required to find the elevation.

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6. Change Point (CP) :- The point on which both the

foresight and back sight are taken during the operation of

levelling is called change point.

7. Fore sight (F.S) :- Is the last reading taken before

the transfer device.

8. Intermediate sight (I.S.) :- Is reading taken between

the back sight and fore sight reading.

9. Elevation of line of sight (H.I) :- Is the imaginary

vertical level determined by the line of sight to the amount

of increase or decrease for sea level (Height of

Instrument).

Benchmarks

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6. Reading a Staff

1.422

• Read the [m], [dm] & [cm]

• Estimate the [mm]

• Check yourself for frequent used

numbers (2/3) or (7/8)


7. Finding the Target

Most telescopes have a targeting system along the top of the barrel

(similar to a rifle target finder). The telescope should be aimed at

the staff using this targeting system prior to trying to find the staff

through the eyepiece.

MOVE TELESCOPE UNTIL TRIANGLE APPEARS OVER STAFF

Target finder (Look at this and beyond towards staff)

Eye-piece

Telescope

Staff Target finder (In line with staff)

Eye-piece

Telescope

Staff


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8. Basic Rules for Leveling

• Always start and finish a leveling run on a Benchmark (BM or

TGBM) and close the loops.

• Keep fore sight and back sight distances as equal as possible.

• Keep lines of sight short (normally < 50m).

• Never read below 0.5m on a staff (refraction).

• Use stable, well defined change points.

• Beware of shadowing effects and crossing waters.


9. Field Notes

Back Inter Fore Point

TH

NB1

NB2

NB1

TH

1.327

3.982

S2

S1

New Benchmark NB1

Tidal Hut TH

New Benchmark NB2

2.365

0.986 2.347

3.724 3.753

1.101


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10. Procedure of leveling

1. The instrument must be check before use!

2. The instrument and level must be stable settled-up

3. The bubble tube must be leveled before the reading

• Beware of sun exposure (will wander)

• Ensure the instruments pendulum is in-limit

4. The instrument must be set up in the middle between two staffs

• Prevents curvature effects

• If impossible, use the same distances, but opposite for the next readings

5. You must not use the parallax screw between the backsight and

foresight readings


6. Readings must be taken 30-50 cm above the ground

• Surface refractions

• Beware also of temperature gradients (inside/outside buildings).

7. Staff should be set up vertically

8. A change plate should be used

9. Leveling must be done in two opposite directions but the same

line (beware of gravity gradients)

10. Staff should be calibrated, especially if INVAR

11. Be careful when crossing rivers (large water surfaces)

• Use “same-time” (mutual) observations

• Repeat it during different times of the day


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• There are a large number of potential sources of errors in leveling.

Many of these are only significant for precise leveling over long

distances. For the short segments of leveling that will occur in

connecting a TGBM to nearby benchmarks there are only four

worth mentioning:

a. Collimation Error

b. Error due to Earth Curvature

c. Error due to Parallax Error

d. Error due to Refraction

11. Leveling Errors


• Line of Collimation – Imaginary line that passes through leveling

instrument at Cross Hairs

a. Collimation Error


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Collimation Error


• When using an optical instrument — both the image and cross

hairs can be focused- if either is imprecisely focused, the cross

hairs will appear to move with respect to the object focused, if one

moves one's head horizontally in front of the eyepiece.

b. Parallax Error


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Parallax Error


• Due to the curvature of the Earth, the line of sight at the

instrument will deviate from a horizontal line as one

moves away from the level.

c. Curvature of the Earth


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35 Ishik University / Sulaimani Assistant Lecturer /Asmaa Abdulmajeed

12. Types of Levelling

1) Simple levelling

2) Differential levelling

3) Fly levelling

4) Profile levelling

5) Cross sectional levelling

6) Reciprocal levelling

1. Simple levelling:-

• When the difference in the elevation of two nearby points is

required then simple levelling is performed.


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2. Differential levelling:-

Performed when the final point is very far from the initial point.


3. Fly levelling

• Performed when the work site is very far away from the

bench mark.

• The surveyor starts by taking BS at BM and proceed towards

worksite till he finds a suitable place for temporary BM. All

works are done with respect to temporary BM.

• At the end of the day the surveyor comes back to original

BM.

• This is called fly levelling.


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4. Profile levelling:-

•Profile levelling, which yields elevations at definite points along a

reference line, provides the needed data for designing facilities such

as highways, railroads, transmission lines.

•Reduced levels at various points at regular interval along the line is

calculated.

•After getting the RL of various points the profile is drawn. Normally

vertical scale is much larger than horizontal scale for the clear view of

the profile.


5. Reciprocal levelling:-

When levelling across river is required then this method is applied to

get rid of various errors.


Documents

SURVEYING 1 CE 215 CHAPTER -3- LEVEL AND · PDF file · 2017-10-07SURVEYING 1 CE 215 CHAPTER -3- ... levelling is called change point. 7. Fore sight ... A change plate should be used