SURVEYING-I

According to RTU syllabus

UNIT-1

PART-4

Correction to Tape measurements-

1. Correction for standardization.
2. Correction for slope
3. Correction for pull
4. Correction for sag
5. Correction for temperature
6. Correction for mean sea level
7. Correction for mis-alignment

Correction for standardization

• If actual length of tape is not equal to nominal length of tape,then correction for standardization is required.

 

Nominal/Designated length of tape = l =20m/30m

Actual /Absolute length of tape = l'

Measured Distance = L

Correct Distance = L'

 

 

 

 

20 m

20 m

• If tape is actually shorter than nominal length,then error will be positive and vice-versa.
• Therefore,correction will be negative.

Error per chain length = M.V.- T.V. =l - l'

 

Error for Measured Distance =L= Error per chain length x no.of times chain kept

=(l -l') x L / l

 

Correction for Measured Distance = L = (l'-l) x L / l

Correction for slope

• The distance measured along the slope between two station is always greater than the horizontal distance is known as slope correction.
• so,it is always negative.

Correction for pull

• If the pull applied to the tape during measurement is more than the standard pull at which the tape was standardized,then length of tape increases.so correction for pull is positive.
• If the applied pull is less than the standard pull,correction for pull is subtractive.

Correction for temperature

• Correction for temperature is positive,if the temperature during measurement is more than the standard temperature at which the tape was standardized and vice-versa.

Correction for sag

• If the tape is standardized on flat and when used is supported between two ends,correction for sag will always be negative.
• It is because chord length will always be less than arc length.

Correction for Misalignment

• If the survey line is not accurately ranged out,the error due to misalignment occurs.
• The measured distance ABC will always be greater than the correct distance AC.
• Hence the error is positive and the correction is negative.

A

B

C

B

1

Correction for Mean sea level

• The measured lengths at different altitudes are sometimes reduced to a common level generally called Mean sea level.
• The measured distance at any altitude '"h"above mean sea level would be greater than the equivalent length at mean sea level.
• so correction will be negative always.

D-L

ADITI SHARMA