Lecture #2 & #3. Introduction and Chain Surveying (W23) PART-II.pdf

In surveying, a baseline is a line between two points on the earth's surface and the
direction and distance between them. In triangulation, the base line is the most important line and
is measured very precisely. This is so because the accuracy of triangulation depends upon the
accuracy of the sides of the triangles computed from the base line. In addition to being a
supplement to angular measurement in triangulation, the base line measurement may also be
used as a base to determine the scale of triangulation.
What is a Base line?
The line on which the framework of the survey is built is known as the base line. The
base line is the most essential line of the survey, and it is usually the longest of the main survey
lines and lies fairly in the middle of the ground contributing to triangles as a reference line. This
line should be drawn on very level ground and measured very carefully and precisely.
Site Selection for Base Line:
In selecting site for a base line, the following requirement should be considered.
 The site should be fairly leveled or uniformly sloping.
 The station points on site should be inter visible.
 Should be free from obstructions throughout the entire length.
 Ground should be firm and smooth.
 The site is selected that well-conditioned triangles is formed.
 The longest of the main survey lines is the base line.Procedure:
 Initially, two points are taken.
 Place the Theodolite on one of the stations and ranging rod on the other station.
 Placed the two or three tripod stand between the two-measuring points. These tripods are
placed at regular intervals.
 Alignment (ranging) of all the tripods is carried out along line.
 After aligning these tripods, ranging rod and theodolite are also replaced with tripods.
 The tripods are placed at a spacing (usually equal) depending upon the length of the base
line.
 Another theodolite is placed in the vicinity of field to check whether all the tripod stands
are at same level or not. If not, then first level the tripods to proceed next.
 The temperature is noted down at each point for temperature correction.
 During length measurement, tension (pull) is produced in the tape which is measured by
the spring balance.
 To find the accurate length, put one end of tape on one tripod stand and another end on
second tripod stand.
 Load is applied on one end of tape when tension is produced in the tape and it is
measured by the spring balance.
 The procedure is repeated till all base line is covered.Difference between the heads of tripods is calculated with the help of theodolite/auto
level by taking different staff readings.
 During this procedure, correction for slope is adopted.
 Total base length = lengths between the individual tripods.
 Different tape corrections are applied to obtain the exact length of base line.
Corrections:
Temperature Correction:
The phenomenon of thermal expansion plays an important Pull/Tension Correction:

1. ENGINEERING SURVEYING
CE02123
Introduction & Chain Surveying
(Part-II)
Department Of Civil Engineering
THE UNIVERSITY OF LAHORE, PAKISTAN
B.Sc. Civil Engineering
2nd Semester
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2. 2
METHOD OF CHAINING ON LEVEL GROUND

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4. 4
METHOD OF CHAINING ON SLOPING GROUND

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P
3P
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6. 6
Aninclinometerorclinometerisaninstrumentusedformeasuring
anglesofslope(ortilt),elevationordepressionofanobjectwith
respecttogravity'sdirection.

7. 7 PROBLEM RELATED TO METHOD OF CHAINING ON SLOPING GROUNDPROBLEM RELATED TO METHOD OF CHAINING ON SLOPING GROUND

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1
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OBSTACLE IN CHAINING

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CHAIN AND TAPE CORRECTIONS

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18. 18 PROBLEM RELATED TO CHAIN AND TAPE CORRECTIONS

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20. 20 PROBLEM RELATED TO CHAIN AND TAPE CORRECTIONS

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23. 23 PROBLEM RELATED TO CHAIN AND TAPE CORRECTIONS

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27. 27 PROBLEM RELATED TO CHAIN AND TAPE CORRECTIONS

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PROBLEMS ON SCALE

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CHAIN SURVEYING
Chainsurveyingisconsideredtobethesimplestmethodofsurveyingin
whichmeasurementsaretakeninthefieldandothersupplementaryworks
likeplottingcalculationsarecarriedoutinoffice.Themeasurementsinchain
surveyingarelinear,angularmeasurementsarenotconsidered.

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36. 36
LARGE-SCALE AND SMALL -SCALE MAPS

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WELL-CONDITIONED AND ILL -CONDITIONED TRIANGLES

38. 38

39. IMPORTANT TOOLS FOR CHAIN SURVEYING
Chain
Tape
Ranging Rods
Arrows
Cross staff or Optical Square (For setting out right angles)
Wooden Pegs
Plumb bob with thread
Prismatic compass with stand
Field Book
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IMPORTANT DEFINITIONS REGARDING CHAIN SURVEYING

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SELECTION OF SURVEY STATIONS

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48. CONVERSION FOR IMPORTANTANT UNITS
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