chain.pptx

Department of Civil Engineering Created By Er.A.B. Jadhav Mob.No 9075009500
Basic Surveying
Presented By
Er. Ashish B.Jadhav
CO:-Compute area of open field using chain ,tape and cross staff

2.1 Chain Survey Instrument
• Metric chain:-
 Chains are the measuring instrument used in surveying
formed by the 100 or 150 links of 4mm galvanized mild steel
wire.
 These links are joined by 3 circular or oval wire rings.
 These rings provide the flexibility to the chains.
 Metric chains are available in 20m. or 30m. in length.
 Length of one link is 20cm (One link means the distance
between the centers of adjacent middle rings).
 The chain consists of many small parts used for handling or
reading the measurements.
• At the ends chain is provided with brass handle with
swivel joint so that it can be easy to roll or unroll the chain
without twisting and knots.

• Metric chain:-
• At every 10th link is
provided with a
tally of one teeth
i.e. for 2 m.,
20th link with a
tally of two teeth
i.e. for 4m. and so
on till 40th link.
This is provided for
the easy reading of
measurements.

• Other types of chain:-
 Steel band or Band chain
 These types of chain consist of a long narrow strip of
steel of uniform width of 12 to 16 mm and thickness of
0.3 to 0.6 mm.
 This chain is divides by brass studs at every 20cm or
instead of brass studs, band chain may have graduated
engraving as centimeter.
 For easy use and workability band chains are wound on
steel crosses or metal reels from which they can be
easily unrolled.
 These steel bands are available in 20m and 30m length
and the width of about 12-16mm.

 Gunter’s chain or Surveyor’s chain
 Gunter chain comes in standard 66ft.
 These chain consists of 100links, each link being 0.66ft or
7.92inches.
 The length 66ft is selected because it is convenient in land
measurements.
o 10 square Gunter’s chains = 1 Acre
o 10 Gunter chains = 1 Furlong
o 80 Gunter chains = 1 mile.
 Engineer’s chain
 This chain comes in 100ft length.
 Its consist of 100 links each link being 1ft long. At every 10 links
a brass ring or tags are provided for indication of 10 links.
 Readings are taken in feet and decimal.

 Revenue Chain
 The standard size of this type of chain is 33ft.
 The number of links are 16, each link being 2 ⅟16 ft.
 This chain is commonly used in cadastral survey..

• Tapes:-
• There are 5 types of tapes available in
surveying for linear measurements and
they are as follows
 Linen Tape
 Linen tape, also known as cloth tape
is a varnished strip made of closely
woven linen.
 The width of the strip is about 12 to
16 mm.
 It is available in different lengths
such as 10m, 20m, 30m, and 50m.
 Both ends of the linen tape are
provided with metallic handles and
the whole tape is wounded in leather
or metal case.

 Linen Tape
 Linen tapes are light in weight and
easy to handle.
 These tapes may shrink when
exposed to water and also elongate
when pulled.
 Hence, these tapes are not suitable
for accurate surveying
measurements.
 These are generally used for
measuring offsets and for ordinary
works.

 Woven Metallic Tape
 The metallic woven tape is an improved
version of linen tape.
 Brass or copper made wires are used as
reinforcement for the linen material.
 Hence, it is more durable than normal
linen tape.
 A brass ring is provided at the end of the
tape which is included in the length of
the tape.
 These tapes are available in different
lengths of 2m, 10m, 15m, 20m, 30m,
and 50m.
 These are used for survey works such as
topographical survey works where minor
errors are not taken into consideration.

 Steel Tape
 A steel tape is made of steel or stainless
steel.
 It consists of a steel strip of 6mm to
16mm wide.
 It is available in lengths of 1m, 5m, 8m,
10m, 20m, 30m and 50m.
 Meters, decimeters, and centimeters are
graduated in the steel strip.
 Steel tapes generally came up with the
metal case with automatic winding
device.
 The tape is withdrawn from the case by
using a hand during measuring and it is
rewound into the case by just pressing
button provided on the case.

 Synthetic Tape
 Synthetic tapes are made of glass fibers
coated with PVC.
 These are light in weight and flexible.
 They are available in lengths of 5m,
10m, 20m, 30m, and 50m.
 Synthetic tapes may stretch when
subjected to tension.
 Hence, these are not suitable for accurate
surveying works.
 However, synthetic tapes are
recommended in place of steel tapes
where it is essential to take
measurements in the vicinity of electric
fences and railway lines, etc.

 Invar Tape
 Invar tapes are made of an alloy which
consists of 36% of nickel and 64% of
steel.
 Invar tape contains a 6mm wide strip and
is available in different lengths of 30m,
50m, 100m.
 The coefficient of thermal expansion of
invar alloy is very low.
 It is not affected by changes in
temperature. Hence, these tapes are used
for high precision works in surveying
such as baseline measurement,
 These tapes should be handled with care
otherwise bends or kinks may be formed.

• Arrow:-
 When the length of the line to be
measured is more than a chain
length, there is need to mark the end
of the chain length.
 Arrows are used for this purpose.
 Arrows are made up of 4 mm
diameter steel wire with one end
sharpened and other end bent into a
loop.
 Length of an arrow is approximately
400 mm.

• Peg:-
 Wooden pegs are used in measuring
a length of a line to mark the end
points of the line.
 The pegs are made of hard wood of
25 mm × 25 mm section, 150 mm
long with one end tapered as shown
in the image.
 When driven in ground to mark
station points they project about 40
mm.

• Ranging Rod:-
 For ranging intermediate points
along the line to be measured,
ranging rods and ranging poles are
used.
 Ranging rods are 2 to 3 m long and
are made of hard wood or steel.
 They are provided with iron shoe at
one end as shown in image.
 They are usually circular in section
with 30 mm diameter and are painted
with 200 mm colour bands of red and
white or with black and white.

• Ranging Rod:-
 If distance is more than 200 m, for
clear visibility they may be provided
with multi coloured flags at their top.
 The ranging rods are occasionally
used to measure
short distances since they are painted
with alternate colour of band 200
mm.
 Ranging poles are similar to ranging
rods except that they are longer.
 Their length varies from 4 m to 8 m
and diameter from 60 mm to 100
mm.

• Line ranger:-
 It is an optical instrument used for locating a
point on a line and hence useful for ranging.
 It consists of two isosceles prisms placed one
over the other and fixed in an instrument with
handle.
 The diagonals of the prisms are silvered so as to
reflect the rays.
 To locate point C on line AB (ref. image) the
surveyor holds the instrument in hand and stands
near the approximate position of C.
 If he is not exactly on line AB, the ranging rods
at A and B appear separated as shown in image
(b).

• Line ranger:-
 The surveyor moves to and fro at right angles to
the line AB till the images of ranging rods at A
and B appear in a single line as shown in image
©
 It happens only when the optical square is
exactly on line AB.
 Thus the desired point C is located on the line
AB.
 Its advantage is it needs only one person to
range.

2.1 & 2.3 Chain Survey Instrument
• Offset:-
 The lateral measurements taken to
the left or right of a survey line to
locate the details such as buildings,
boundaries, fences and road.
 Types:
 Oblique offset :- offset taken at
an angle other than 90º to a
survey line.
 Perpendicular offset:- offset
taken at an angle of 90º to a
survey line.

• Optical square:-
 It is more accurate than the cross-staff and is
used for setting out accurately the long offsets. It
is a small compact hand instrument based upon
the principle of reflection.
 Principle of Optical Square:
oIf there are two plane mirrors whose reflecting
surfaces make a given angle with each other and if a
ray of light is reflected successively from both of
them,
oThen the angle between the first incident ray and
the last reflected ray is twice the angle between the
two mirrors.
oSince we want to set out right angles with the
optical square, it follows that the two mirrors in it
must make an angle with each other equal to half the
right angle i.e 90°/2 = 45°

• Open cross staff:-
 The simplest form of cross-staff is the open
wooden cross-staff shown in image.
 It consists of a round or square piece of wood
about 4 cm thick and varying form 15 cm to 30
cm in diameter or side mounted on an iron shod
wooden staff about 2.5 cm diameter and 1.5 m
long.
 The disc is provided with two saw cuts about 1
cm deep at right angles to each other, giving two
lines of sight.
 The modified form of the open cross-staff is the
metal arm cross-staff in which the wooden head
is replaced by four metal arms with vertical slits
for sighting through at right angles to each other.

2.2 Chain Survey Basics
• Survey Station:-
 Survey Stations is a point of importance at the beginning and end of chain
line.
 There are two types of survey stations:
 Main Station
 These are the end of survey line i.e. which connects boundaries.
 Line joining Main Stations is called Main Survey Line or Chain
Line.
 They are represented by Triangle, Capital letters A B... Or number
1 2.
 Subsidiary or Tie Station
 These are the points selected on main line, where it is necessary to
run auxiliary lines to locate interior details such as corner, tree,
building etc.
 Lines joining tie station are called Tie Lines or Subsidiary Lines
 They are represented by Circle, Small letters a, b,

Selection of Survey Station:-
The following points should be kept in mind while selecting a
station:
The stations should be mutually inter-visible.
Main principle of chain survey should strictly be observed.
If possible, line through the whole length of area should be drawn.
All triangles should be well defined.
A check line should be provided in each triangle.
Survey lines should be as few as possible.
A number of tie lines should be drawn.
Position of survey lines should be such that to avoid obstacles to
chaining and ranging.
It should be on level ground.
The sides of triangle should pass as close to the boundary as possible.

• Base Line:-
 The longest of the chain lines used in making a survey is generally
regarded as Base line.
 It is the most important line because it fixes up the direction of all
other lines, since on base line, is built framework of a survey.
 It should be laid on level ground, as possible through the center
and length of the area.
 It should be correctly measured and should be measured twice or
thrice.
• Check Line:-
 A check line also called proof line is a line joining the apex of a
triangle to some fixed point on the opposite side.
 A check line is measured to check the accuracy of the framework.
 Thus there is a complete check on the field measurement as well as
on the accuracy of the plotting work.

• Tie Line:-
 A tie line is a line joining fixed points termed as Tie station on the
main survey lines.
 A tie line usually fulfill a dual purpose i.e. it checks the accuracy of
the framework and enables the surveyor to locate the interior
details which are far away from the main chain line.

• Steps in Chain survey:-
 Chain survey is the simplest method of surveying.
 In this survey only measurements are taken in the field, and the rest
work, such as plotting calculation etc. are done in the office.
 This is most suitable adapted to small plane areas with very few details.
 If carefully done, it gives quite accurate results.
 The necessary requirements for field work are chain, tape, ranging rod,
arrows and sometime cross staff.
 Principle of Chain Surveying:-
 The whole area that need to be surveyed is divided into a skeleton
of framework that consists of a number of well connected network
of well conditioned triangles. This is the principle
of Triangulation.

• Well conditional Triangle & Ill
conditional Triangle:-
 The triangles with angle(A) in
the range 30<A<120 is called as
Well-conditioned Triangles.
 An equilateral triangle is the best
well-conditioned triangle (Ideal
Triangle) possible.
 An ill-conditioned triangle is a
triangle with an internal angle
(A) in the range 120<A<30.

 It is a system of surveying in which sides of various triangles are
measured directly in the field and NO angular measurements are
taken.
 It is adopted when Level of accuracy required is not high.
 Chain survey steps:
 Reconnaissance & Index Sketch
 The preliminary inspection of the area to be chain
surveyed is called reconnaissance.
 The surveyor inspects the area to be surveyed, survey or
prepares index sketch or key plan.
 Walk the whole area and thoroughly examine the ground,
note the position of boundaries, road, and river etc.,
various difficulties to chain lines, select stations, and
prepare neat sketches called index sketches or key plan.

• Chain survey steps:
 Marking stations
 Stations are marked with ranging rod, or wooden peg,
driving a nail or spikes if hard surface, or embedding
stone with a cross mark.
 Reference sketches
 After marking the station should be referenced i.e. located
by measurement called ties taken from 3 permanent points
which are easily identified such as corner of building
 Running survey line
 After the preliminary work, chaining is started from base
line and carried throughout all the line of the framework
continuously.
 So chain is laid and kept lying, offset are taken to locate
the nearby details. Make ranging wherever necessary.
 Measure the change and offset and enter in the field book.

• Suitability of Chain survey:-
 Chain Survey is Suitable when:
 Ground is fairly level and simple
 Plans are required on large scale e.g. fields
 When area is small in extent.
 Chain Surveying is Not Suitable when:
 For Large Areas
 When too many details are required
 Wooded countries
 Undulating areas

• Obstacles in Chaining:-
 It sometimes happens that a survey line passes through some object
such as a pond, a building, a river, a hedge etc. which prevents the
direct measurement of that part of the line which the object intersects.
The interfering object in such a case is called as Obstacle.
 It is necessary to overcome obstacles so that chaining may be continued
in a straight line.
 Special methods are, therefore, employed in measuring distances across
the obstacles.
 The Three Main Obstacles in chaining of a line are of the following
types:
 Chaining Free, Vision Obstructed
 Chaining Obstructed, Vision Free
 Chaining and Vision Both Obstructed.

• Type 1. Chaining Free, Vision
Obstructed:
 In this type of obstacles, the ends of
the lines are not inter visible e.g.
rising ground, hill or jungle
intervening.
 Their are two cases may arise:
 Case 1:- Both ends may be
visible from any intermediate
point lying on the line such as in
the case of a hill. The obstacle of
this kind may easily be crossed
over by reciprocal ranging and
length measured by stepping
method of chaining.

Obstructed:
 Case 2:-
 Both ends may not be visible from any
intermediate point such as in the case of a
jungle.
 The obstacle of this kind may be crossed
over by “Random line method”. In fig.
 let AB be the line whose length is
required.
 From A, run a line AB’ called a random
line, in the approximate convenient
direction of AB and continue it until point
B is visible from B’ Chain the line to B’
where BB’ is perpendicular to AB’ and
measure BB’.

Obstructed:
 Case 2:-
 Now measure the distance AC, AC’,
CC’, AD’, DD’as shown in figure.
 From ∆ACC’And ∆ADD’
AC/CC’=AD/DD’
AD=AC/CC’ *DD’

• Type 2. Chaining Obstructed, Vision Free:
 The typical obstacle of this type is a sheet of water, the width of
which in the direction of measurement exceeds the length of the
chain or tape.
 The problem consists in finding the distance between convenient
points on the chain line on either side of obstacle.
 Two cases may arise:
 When the obstacle can be chained around, e.g. a pond, a
thorny hedge etc.
 When the obstacle cannot be chained around e.g. a river.

• Type 2. Chaining Obstructed,
Vision Free:
 Case 1:- The distance between two
points A and B on either side of the
pond may be determined by any of the
following methods convenient at site:
 Set out equal perpendiculars AC and
BD as shown in figure (a) Measure
CD which is equal to AB.
 Erect perpendicular AC as shown in
figure (b) of such a length that CB
clears the obstacle and measure AC
and CB.
By the Pythagoras Theorem
AB² =√ CB²-AC²

• Type 2. Chaining Obstructed, Vision
Free:
 Case 2:- Any one of the following methods may
be employed to find the width of the river along
the direction of the chain line:
Select two points A and B on the chain line on
opposite banks of the river.
 From A and C, erect perpendicular or parallel
lines AD and CE, such that E, D and B are in line.
Measure AC, AD and CE.
If a line DF is drawn parallel to AC, meeting CE
in F, the triangles ABD and FDE are similar.

Free:
the direction of the chain line: Type 2
 Select two points A and B on the chain line on
either side of the river.
 Set a perpendicular AC and mark its midpoint
D.
 From C, erect CE perpendicular to AC such
that E, D and B are in the same range and
measure CE.
 Then triangles ABD and CED are congruent.
Therefore AB = CE.

Free:
the direction of the chain line: Type 3
 At A, set out a line AC in a convenient direction
so that C is the foot of the perpendicular from B
on AC.
 Produce CA to D and measure AD = AC. At D,
erect a perpendicular DE, E being a point on
the chain line.
 Then triangles ABC and AED are similar
Therefore AB = AE (the oblique width of the
river.

• Type 3. Chaining and Vision Both
Obstructed:
 A building is a typical example of this class
of obstacles. The problem in this case
consists both in prolonging the line beyond
the obstacle and finding the distance across
it.
 Select two points A and B on the chain
line.
 At A and B, erect equal perpendiculars AC
and BD.
 Join CD and produce it past the obstacle.
 Select two points E and F on it. At E and F,
set out perpendiculars EG and FH, each
equal in length to AC.
 The points G and H then lie on the chain line
and BG = DE.

2.3 Ranging
• Ranging:-
 The process of fixing or establishing intermediate points
to facilitate measurement of the survey lines are called as
Ranging.
 The intermediate points are located by means of ranging
rods, offset rods and ranging poles.
 The process of ranging can be done by two methods:
 Direct Ranging
 Indirect Ranging

2.3 Ranging:-Direct Ranging
• Direct Ranging:-
 Direct ranging is the ranging conducted when the intermediate points are
intervisible.
 Direct ranging can be performed by eye or with the help of an eye instrument.
Ranging by Eye
As shown in figure let A and B are the two intervisible points at the ends of the
survey line.
The surveyor stands with a ranging rod at the point A by keeping the ranging rod
at the point B.
The ranging rod is held at about half meter length.
The assistant then takes the ranging rod and establishes at a point in between AB,
almost in line with AB.
This is fixed at a distance not greater than one chain length from point A.

2.3 Ranging:-Direct Ranging
• Indirect Direct Ranging:-
 Indirect ranging is employed when the two points are not intervisible or the
two points are at a long distance.
 This may be due to some kind of intervention between the two points.
 In this case, the following procedure is followed.
Two intermediate points are located M1 and N1
very near to chain line by judgment such that from
M1, both N1 and B are visible & from N1 both M1
and A are visible.
At M1 and N1 two surveyors stay with ranging
rods. The person standing at M1 directs the person at
N1 to move to a new position N2 as shown in the
figure. N2 must be inline with M1B.
Next, a person at N2 directs the person at M1 to
move to a position M2 such that it is inline with N2A.
Hence, the two persons are in points are M2 and N2.
The process is repeated until the points M and N are
in the survey line AB.

2.4 Errors in Length
In general, the distance measurement obtained in the field will be in error. Errors
in the distance measurement can arise from a number of sources:
 Instrument errors:
 A tape /chain may be faulty due to a defect in its manufacturing or from
kinking.
 Natural errors:
 The actual horizontal distance between the ends of the tape can vary due to
the effects of
 Temperature,
 Elongation due to tension
 Sagging
 Personal errors:
 Errors will arise from carelessness by the survey crew:-
 poor alignment
 tape not horizontal
 improper plumbing
 faulty reading of the tape

2.4 General Errors in Length
Erroneous Length of the Chain or the Tape
• This is the error due to the wrong length of the chain which is
considered as one of the serious error
• If the length of the chain is long, then the measured distance is
smaller and the error is negative.
• And when the length of the chain is short, then the measured
distance is long. Hence the error is positive.
• Time to time checking of the chain helps to provide adequate
corrections.
Errors due to Inefficient Ranging
• Inefficient ranging implies the measurement by placing the
chain out of the survey line.
• This mistake always gives a longer distance value. Hence the
error is a positive error which is also a cumulative error type.

 Errors due to Inefficient Straightening
• While measuring a sloped or irregular ground,
• the chain must be held straight.
• Otherwise the resultant value measured is greater than the true length.
• This hence causes a cumulative positive error
 Errors due to Careless Holding and Markings
• This error is caused due to an inexperienced chain man.
• Sometimes, the follower may hold the handle to one side of the arrow
or to the other end.
• The leader trusts his activity and proceeds the work and marks the
points.
 Error due to Sag in Chain
• This is a cumulative positive error.
• While measuring a sloped ground or stepped ground, there are chances
for the chain to sag and the value obtained is higher.
• Hence the error is positive.

 Personal Mistakes
• Displacement of Arrows: Any change in position of the arrow during the
chaining activities completely affects the original location of the arrow.
Hence it is recommended to mark a point on the ground while fixing the
arrow.
• Misreading: Certain confusion while reading tally of a 5m and 15m chain,
and confusing between 6 and 9 are some of the mistakes faced while
reading the measurements.
• Miscounting the Chain Length: This error can be avoided by following a
systematic procedure to count the number of arrows.
• Erroneous Booking: Sometimes, the surveyor may hear the reading wrong
and write it on the book. To avoid this the chainman must say the reading
loud and the surveyor should repeat it loud and enter the field book.
 Errors due to Variation in Pull
• A pull more than the calibrated pull of the chain brings some error.
• The chainman either apply more or less pull, which makes the error
cumulative.

2.5 Principle of Triangulation
 Principle of Triangulation
• Entire area to be surveyed is
converted into framework of
triangles If the length and
bearing of one side and three
angles of a triangle are measured
precisely, the lengths and
directions of other two sides can
be computed.
• This method of surveying was
first introduced by a Dutchman
called Snell

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