introduction to surveying slide

1. CHAPTER TWO
MEASURMENT OF HORIZONTAL
DISTANCES
1

2. 2.1 chain surveying
• Definitions:- Chain Surveying is a kinds of
surveying which is concerned in determining the
linear measurements b/n two points on the
surface of the earth.
• There are two methods of determining the
distance b/n two points on the surface of the
earth .
1. Direct measurements:- In these case distances
are directly measured by means of chain, tape etc.
2. Indirect (commutative methods):- In this case
distance are determined by calculation eg. in
triangulations traversing.
2

3. Instruments for Measuring Distance
• The materials for measuring horizontal distance directly are
o Tape:- either metallic tape, steel tape, cloth tape plastic tape.
o Steel band. (Surveyors band)
o Chains:- is measuring instruments which has It is available in lengths
varying from 15m to 100m
o EDM (Electronic Distance Measurement):- instruments that work using the
invariant velocity of light or electromagnetic waves in vacuum
 The other instruments which are involved in measuring a distance
(horizontal) are i.e to make station.
 Ranging Rods:- a circular section of 2m, 2.5m or 3m pointed with red &
white.
 Pegs:- these are either wooden or steel which are either circular or
square with length 30cm.
 Tripod:- in hard or paved pound tripod is used to support the ranging
rods.
 Plumb bob:- This is used to transfer the end points of the chain where
measuring distance in a hilly terrain. It is also to test the vertically of
ranging rod leveling etc.
3

4. Horizontal Distance Measuring tools
tripod
Tape
pegs
Plum bob
EDM
4

5. Principle of chaining
• In most of Engineering Surveying Steel band is
used.
• So to measure the length of a line which is
greater than the length of steel band the
following principle should be followed.
• Person is needed in chaining i.e with two chain
man.
Leader chain man (with ranging rod & peg).
Follower chain man.
One who is recording measurements (optional).
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6. • Example 1 (on flat ground):- To measure the length
of line A which is 800m.
• Example 2 (On slopped ground): To measure a
distance AB.
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7. Correction applied to steel taping error
• Systematic errors in taping are due to
(1) incorrect tape length,
(2) tape not horizontal,
(3) fluctuation in temperature of the tape,
(4) in correct tension or pull,
(5) sag in tape,
(6) incorrect alignment and
(7) tape not straight.
7

8. 1. Correction for temperature: - The length of the tape
increases while the temperature is increased and
decreases if the temperature is lowered
Where L = measured length of a line
t = mean temperature during measurement in 𝑜𝑐.
ts = nominal temperature of standardization.
Ct = correction due to temperature
 = co-efficient of linear expansion.(6.5*10−6
oF)or
11.2*10-6oc
• If the Tfield>Tstan the correction is positive Tfield>Tstan it is
negative.
• Example: You must lay out two points that are exactly 100m
apart. Field conditions indicate that standard conditions
apply except the measured temperature is 27oC. Determine
the distance to be laid out. (Ts=20oc)
ANS: Ct = 11.2x10-6 /oC (27-20 oC) 100.000 m = +0.00784 m
8

9. 2. Correction for Sag:- When the tape is suspended
from two support in air, is assumes the shape of
centenary.
Lc – L = Cs
CS= =
Where Cs = Correction for sag
w = weight per unit length
l = measured length of open
p = pull applied during measurement
Example: calculate the horizontal length b/n two
supports, if the recorded length is 30.6m, the tape
weights is 15N/m and applied tension is 20N.(-0.069)9

10. 3. Correction for tension:- If the pull applied to the
tape during measurements is more than it is
standardized its length increase and the measured
distance become less than the actual.
• Correction for tensions is there for positive.
Let P = the tension of pull at field (N).
Ps = standardized tension. (N).
L = length measured.
A = Cross – sectional of steel band
E = Yoong’s modulus of elasticity of the steel bond.
Cten = Correction for tension
10

11. • Example : A heavy 50‐m tape having a
cross‐sectional sectional area of 0.05 cm2 has
been standardized at a tension of 5.5 kg. If E =
2.10 x 106
kg/cm2 , determine the elongation of
the tape if a pull of 12 kg is applied .
• 𝐶𝑡𝑒𝑛 =
12𝑘𝑔−5.5𝑘𝑔
0.05𝑐𝑚2∗2.1∗106 𝑘𝑔
𝑐𝑚2
0.5cm=3.1*𝟏𝟎−𝟓
cm
11

12. 4. Correction for Altitude-: If the surveying is
connected to the functional mapping of the
country, the distance will need to be reduced to
the common datum at that system normally.
12

13. The correction for altitude for surface work is
negative & positive for tunneling work or mining
work below MSL.
Example: Let R=6,37 3,002m, LH=160,934m, then
calculate correction for altitude.
𝐶𝑎𝑙 =
160934𝑚
6373002𝑚
= 0.025
13

14. 5. Correction for slope: - The distance measured
along the slope between two station is always
greater than the horizontal distance is known as
slope correction.
• This is always negative.
Where h = elevation differences between points
• similarly correction for slope if angle  is known.
14

15. Example: if h=1.37m, L=106.86m and 𝜃 = 60°
then determine the slope correction.
Cslope= -106.86m(1-cos60°)=-53.43m
Or
Cslope=
−1.372 𝑚
2∗106.86𝑚
=-0.0087m
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16. 6. Correction for alignment: Generally when a
surveying line is set out obstruction to follow
line may be composed of two or more straight
lines subtending on angle other than 1800
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17. 7. Correction for standard length:
• If you have given a tape for measuring a length at
field. Before using the tape its actual length
should be ascertained by comparing it with a
standard tape of known length.
• The designated nominal length of the tape is its
designated length e.g 30m or 100m
• The absolute length of the tape is it actual length
under specified condition.
• The absolute length of tape is seldom & Equal to
nominal length of the tape.
17

18. where:
CL= is the correction applied to the recorded measurement
l = is the actual tape length
l’= is the “nominal” tape length
L=is the recorded measurement
Example: A measurement of 171.278 m was recorded with a
30-m tape that was only 29.996 m long under standard
conditions. What is the corrected measurement?
L=171.278m, l=29.996m, l’=30m
𝐶𝐿 = L
𝑙′−𝑙
𝑙
= 171.278m
30𝑚−29.996𝑚
29.996𝑚
=0.228m
18

19. Degree of Accuracy in Chaining
• Some conditions affecting the accuracy are:
 Fitness of graduation of the chain.
 Nature of the ground.
 Time and money available
 Weather etc.
• Application of chain Surveying
 The main purpose of chain Surveying is to carry out one of
the following purpose.
 To have necessary data’s for exact description of the
boundaries of plot of lands.
 To determine the area of plot of land.
 To prepare accurate plan of plot of land.
 To determine the boundaries of plot of lands which is
previously surveyed.
 To divide the plot of lands in to a number of smaller unit.
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20. Technical terms and their definition
• Some of the most technical terms which are use in
applications of chain surveying are.
• Main survey station: - the principle of chain surveying is to
divide the areas in to a number of triangles
• Main survey line: - The chain line joining the two main
stations.
• Subsidiary survey station: - the stations which are selected
on the main survey line for running auxiliary lines
• Subsidiary survey lines: - is the chain line going the main
survey stations and subsidiary survey stations.
• Based line:- is the longest of main survey lines
• Check line:- to check the accuracy of the field.
• If the measured length of a check line agrees with the
scaled off the plan, the survey is accurate.
20

21. • A, C, D, B=main
survey station
• AB, AC, CD, BD, =main
survey line
• E, F, =subsidiary
stations
• BF, CF= subsidiary line
• AD= base line
• GH, MN= check line
• L1, L2= offset lines
21

22. • Offset: the positions of details i.e. boundaries,
roads, churches, stream, bends etc. are
located with respect to the chain line by
measuring their distance right or left of the
chain lines. Such lateral measurements are
called offset
• There are two kinds of offset.
– Perpendicular offsets: - when the lateral
measurements are perpendicular to chain lines.
– Oblique offsets:- when the lateral measurements
are made of any angle to the chain line
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23. 23

24. Measurements of perpendicular offsets
• The offsets are generally measured either
metallic or steel tapes depending up on the
accuracy required of surveying.
• For every offset the following information has to
book.
I. The distance along the chain line or change.
II. The length of the offsets.
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25. 1. Cross staff
1.1 Open cross staff: - it is the simplest types of cross staff,
which is commonly used.
• It consists of head and leg.
• The head is wooden block octagonal or round, about 15
cm side or 20cm diameter and 4cm deep.
• The wooden block is provided with two cats 1cm deep at
right angle to each other for establishing two line of
rights.
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Instruments for measuring right angles

26. 26
1.2. French cross staff:-
• It consists of octagonal brass box with slits
cut in each face so that the opposite pairs
form a sight line.
• The instruments may be mounted on a
short ranging rods, and to set out a right
angle

27. 27
1.3. Adjustable cross staff:-
 It consists of a brass cylinder tube divided at the
middle.
 The lower potions remains fixed and upper portions
can be rotated relative to the lower one by circular
rack.
 Sighting slits are provided in the both parts.
 The lower part is graduated in to degrees and their sub-
divisions while the upper one carries a vernier.

28. • Example for procedures is open cross staff: for siding
the foot of perpendicular offsets, proceed as under.
Chain line B A
• The cross staff is held vertically on the chain line where
perpendicular from an object is expected to meet.
• Turn the cross staff until one pair of opposite slits, is
directed to a ranging rod at A.
• Look through the other pair of slits and see if the points
to which the offset is taken, is bisected (C)
• If not, the cross staff is moved forward or backward on
the chain line tangented to A and bisect C.
• Care should be taken while holding the cross staff
vertically. 28

29. 29
Optical square
Prism square