Linear measurement a Part of surveying

1. ELEMENTS OF CIVIL ENGINEERING
SAGAR DOBARIYA
Asst. professor
Civil Engineering Department
Om Engineering College, Junagadh.

2. LINEAR MEASUREMENT

3. There are tree method of linear measurement
1. Direct method :
 the distance is actually measured during field work
using chain or tap
2. Optical method :
 Principle of optics are used.
 The instrument used for making observations is called
tacheometer.
3. E.D.M. method :
 Electromagnetic distance measuring instruments used.

4.  1. Chain
 2. Tapes
 3. Arrows
 4. Ranging road and offset road
 5. Pegs
 6.Plumb-bob

5. 1. Chains :
 Various types of chain used in chain survey
1. Metric chain
2. surveyor’s chain
3. engineer’s chain
4. Revenue chain
5. Steel band
1. Metric chain :
 This chain consists of galvanized mild steel wire of 4mm
diameter known as link
 The end of the links are bent into a loop and connected
together by means of three circular ring which provide to
flexible of chain.

6.  Both ends of the chain chain have brass handles
 In metric chain length of one link is 20 cm.
 At every one meter length of chain a small brass ring is
provided it is also provided in every 5 m length of chain.

7.  Metric chains are available in length of 20 m and 30m.
 As the length of one link is 20 cm a 20m long chain
consist of 100 links and 30m long chain 150 links
provide.
 Length of chain is embossed on the brass handles of the
chain.
No. Chain type Long Links provide
2 surveyor’s chain 66 feet 100 (every provide in 0.66 ft.)
3 engineer’s chain 100 feet 100 (every provide in 1 ft.)
4 Revenue chain 33 feet 16 links

8. 2. Tapes :
 Tapes are used for more accurate measurements.
 Tapes are classified based on the material
1. Cloth or linen tape
2. Fiber tape
3. Metallic tape
4. Steel tape
5. Invar tape

9. 1. Cloth or linen tape :
 This type of tape are generally 10m, 20m, 25m and 30m
long in length and 12 to 15mm wide.
 They are generally used for offset measurement.
2. Fiber glass tape :
 These tape are similar to linen and plastic coated but these
are made of glass fiber.
 These tap are available in length of 20m, 30m and 50m.
3. Metallic tape :
 A linen tape reinforced with brass or copper wire to prevent
stretching or twisting of fibers is called metallic tape.
 It is commonly used for taking offset in chain surveying.

10. 3. Arrows :
 Arrows are made of tempered steel wire
of diameter 4mm.
 One end of the arrow is bend into a ring
of diameter 50mm and the other end is
pointed.
 Its overall length is 400mm
 Arrows are used for counting the number of chains
while measuring a chain line.
 An arrow is inserted into ground after every chain
length measured on the ground.

11. 4. Ranging rod and offset rods :
 Ranging rod are used for ranging some
intermediate points on the survey line.
 Ranging rod are generally 2 to 3m in
length and are painted with alternate
bands of black and white colors with
length of each equalizing 20cm.
 If the distance is long a road of length
4 to 6m is used
 Offset rod is similar to ranging rod with
the exception that instead of the flag.

12. 5. Pegs :
 Pegs are made of timber or steel and they are used to mark
the position of the stations or terminal points of a survey
line.
 Wooden pegs are 15cm long and are driven in to the ground
with help of a hammer.
6. Plumb-bob :
 Plumb-bob is used to transfer points on the ground.
 It is also used for fixing the instruments exactly over the
station point marked on the ground by checking the center
of the instrument
 Plumb-bob is thus used as centering aid in theodolites and
plane table.

13.  When the length of a line exceed the length of the
chain to proceed in a straight line, intermediate points
are needed to be established between the two station.
 The process of establishing intermediate points on a
straight line between two end point is known as ranging
 Ranging must be done before a survey line is chained.
 There are two methods of ranging
1. Direct ranging
2. Indirect ranging or reciprocal ranging

14. 1. Direct ranging :
 When intermediate ranging rods are fixed on a straight
line by direct observation from end stations, the process
is known as direct ranging.
 Direct ranging is possible when the end stations are
instervisible.
 The ranging will be perfect, when the three ranging rod
coincide and appear as a single rod.

15. 1. Indirect ranging :
 When the end stations are not intervisible due to there
being high ground between them, intermediate ranging
rod are fixed on the line in an indirect way this method
is known as indirect ranging or reciprocal ranging.

16.  Suppose A and B are two end stations which are not intervisible
due to high ground existing between them
 Suppose it is required to fix intermediate point between A and B,
two chain men take up position at X1 and Y1 with ranging rods in
their hands.
 The chainman at X1 stands with his face forward B so that he
can see the ranging rods Y1 and B.
 Again the chainman at Y1 stands with his face forwards A so
that he can see the directing rods at X1 and A.
 The chainman proceed to range the line by directing each
other alternately.
 The chainman at X1 directs the chainman at Y1 to come to the
position Y2 so that X1,Y2 and B are in the same straight line.
 Again the chainman Y2 directs the chain man at X1 to move
to the position at X2 so that Y2,X2 and A are in the same
straight line.

17.  this instrument is used for perpendicular offset only
Principle of optical square :
“ the angle between the incident
ray and the reflected ray is twice
the angle between the mirrors.”
Working of optical square :
 The optical square consist of a
Circular box 50mm in diameter
And 12.5mm in depth.
 The box has tree slits at E,F and
C.
 In line with the top opening at E and F, a glass H silvered at
top and plain at bottom is fixed.

18.  It faces towards E.
 The opposite of opening C a silver painted glass and it
is a fixed so that the inclined edge of glass that’s make
a angle of 45*.
 when opening C face toward object for offset the image
will strike to the index glass I and reflected to
horizontal glass (H).
 The image received from glass I will be reflected and
received by a surveyor holding the instrument and
looking through opening E.

19.  This instrument is simplest from among all and consists
of four metal arms with vertical slits for sighting
through at right angles to each other show in fig.

20.  Two person are required for this instrument
 One pair of vertical slit is to bisect ranging rod at the
end of the given chain line by standing on the chain
line and other pair of vertical slit is required to be in
line with a ranging rod at object for perpendicular
offset from object to chain line.
 The vertical point is marked on the chain line to
measure perpendicular offset and chainage.
 To set out angle of either 45* or 90*.
 French cross staff is used.

21.  linear measurements are made by means of a steel or invar
tap
 Before use it is desirable to ascertain its actual length by
comparing it with
 The standard of known length
 The tape is not used on the field under standard condition of
temperature.
 It is necessary to apply the following correction to the
measured length of a line in order to obtain its true length.
1. Correction for absolute length
2. Correction for temperature
3. Correction for pull
4. Correction for sag
5. Correction for slop

22. 1. Correction for absolute length :
 Nature of correction (+ ve or – ve cumulative)
Ca = L * C
l
where, Ca = correction for absolute length
L = measured length of a line
C = correction per tape length
l = designated length of a tape
Ca

23. 2. Correction for temperature :
 Nature of correction (+ ve or – ve cumulative)
Ca

24. 3. Correction for pull :
 Nature of correction (+ ve or – ve cumulative)
 E = 2.1 * 10’7 for steel
 E = 1.5 * 10’7 for invar

25. 4.Correction for sag :
 Nature of correction (– ve cumulative)
where, Cs = correction for sag
l = distance between support
w = weight of the tape
p = pull applied

26. 5.Correction for slop :