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25 November 08 Unit 2 :Chain Surveying 1
Unit 2: Chain SurveyingUnit 2: Chain Surveying
25 November 08 Unit 2 :Chain Surveying 2
Topics coveredTopics covered
Different methods for linear measurement, instruments for chaining
Different types of Chains/Tapes
Ranging - Direct, Indirect, chaining on sloping ground
Chain surveying: survey station, survey line, locating the ground features with the help of offsets.
Chain surveying, fieldwork & office work
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2.1 Linear measurement- Basics2.1 Linear measurement- Basics
One of the basic function in surveying Always horizontal not sloping
distance No way to check the error other
than remeasuring A
B
Inclined distance AB is not correct
Horizontal distance is correct
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2.1 Linear measurement 2.1 Linear measurement methodsmethods
Methods
Electronic methodsBy optical meansDirect measurements
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2.1 Direct measurements2.1 Direct measurements
Instruments such as Pacing Passometer Pedometer Odometer or Speedometer
Rough methods for preliminary survey
Check of large mistakes in measurement made by more precise method
Unsuitable in irregular and sloping ground
Precision – 1/50 to 1/200
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2.1 Taping / Chaining 2.1 Taping / Chaining
Chaining or taping carries same meaning Use of either chain or tape. One of the accurate method of direct measurements This method is basis for most surveying. Precision
1/1000 to 1/5000 (ordinary land survey)
Use of chain or tape Chain (Early 1600s) Steel tape in use by early 2000s Tape is very common nowadays.
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2.1 Instruments for 2.1 Instruments for chaining/tapingchaining/taping
Chain/tape
Arrows
pegs
Ranging rods
Plumb bob
Hand level
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2.1 Instruments for 2.1 Instruments for chaining/tapingchaining/taping
Arrows 10 arrows
Contd….
Pegs Station position Terminal points of survey line
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2.1 Instruments for 2.1 Instruments for chaining/tapingchaining/taping
Ranging rods Used to range intermediate points on survey line Length 2 m ( very common) or 3 m Bands of 20 cm painted alternate colour( red & white, black &
white)
Ranging poles Similar to ranging rod but big in size Used in case of long lines Used to range intermediate points on survey line
Contd….
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2.1 Instruments for 2.1 Instruments for chaining/tapingchaining/taping
Plumb bob Verticality of ranging pole Transferring the points to ground Also used for centring purpose in
other surveying methods.
Contd….
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2.2 Different types of chain/tape2.2 Different types of chain/tape
Chain (Absolute equipment at present) Metric chain (available in 5,10,20
meter) Gunter’s or surveyor’s chain (66 ft of
100 links) Engineer’s chain (100 ft of 100 links) Revenue chain (33 ft of 16 links) Steel band or band chain ( 20 or 30 m)
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2.2 Different types of chain/tape2.2 Different types of chain/tape
Tape Cloth or Lenin tape Metallic tape Steel tape Invar tape (Alloy of nickel 36% & steel)
Contd….
Steel Tape Linen Tape Metallic TapeCloth Tape
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2.3 Ranging 2.3 Ranging
When the length of survey line is greater than chain or tape length Process of establishing intermediate points
Methods Direct Ranging Indirect Ranging
A B
> one tape length
Intermediate points
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2.3 Direct ranging 2.3 Direct ranging
Direct ranging When two end points are intervisible Either by eye or through optical instruments such as
Line ranger Theodolite
Code of signals used to direct assistant
AP
B
Transverse movement
< one tape length
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2.3 Indirect ranging 2.3 Indirect ranging
Indirect ranging When two end points are not intervisible With the aid of two intermediate points very near to the line
A B
NM
BA
M N
N3
N 2
M2
N1
M3
M1
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2.3 Chaining/taping over sloping 2.3 Chaining/taping over sloping ground ground
Methods Direct method or method of stepping Indirect method
With the aid of vertical angle measurement With the aid of difference in level measurement Hypotenusal allowance
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2.3 Chaining/taping over sloping 2.3 Chaining/taping over sloping ground ground
Direct method or stepping method Convenient to proceed down-hill Tape shall be horizontal Sufficient pull to avoid sag Lengths of steps inversely proportion to degree of slopes.
A
B
l4
l3
l2
l1
D = (l1+l2+l3+l4)
Contd….
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2.3 Chaining/taping over sloping 2.3 Chaining/taping over sloping ground ground
Indirect method (Vertical angle measured) Clinometer to measure vertical angle
D1 = s1×cosΦ1
The required horizontal distance (D) =∑s cosΦ
D2
Φ1
Φ2
s1
s2
C
B
A
D1
Contd….
Indirect method (difference in height) Level machine is used
to measure h to compute D.D = √( s 2 - h 2 )
D
h sA
BC
Indirect method (Hypotensual allowance)
B
A’
C
A
θ1 chain
1 chain
BA / = BC = 1 CHAIN
BA = 1 CHAIN × sec θ
AA / = BA - BA / = 1 CHAIN ( sec θ – 1)
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2.4 Chain surveying2.4 Chain surveying
What is chain surveying?Principle of chain surveying Triangulation
Survey stations Main station (A, B, C,…E) Subsidiary stations (F, G, H) Marking of stations
Survey lines Main survey lines Base lines Check lines Tie lines
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2.4 Survey stations & survey lines2.4 Survey stations & survey lines
Station Mutually visible
Survey lines Few as far as possible Must have one base line Pass through level ground Form well-conditioned triangle Sufficient check line
Short offset
Should not pass through obstacle
Should fall within the boundaries
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2.4 Locating the ground 2.4 Locating the ground featuresfeaturesOffsets- lateral distance of an object from survey line.Offsets should be as small as possibleTypes Perpendicular – less measuring on ground Oblique Method of ties
P Q
AC
P
B900
BA
P
C
≠ 900
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2.4 Locating the ground 2.4 Locating the ground featuresfeatures
Swing of the tape on chain line
Shortest distance is perpendicular offset P
Contd….
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2.4 Locating the ground 2.4 Locating the ground featuresfeatures
Offsets are taken in the order of their chaninage.
Number of offsets depends upon the shape of objects Straight wall, zigzag wall, road
with constant width
Constant width road
Boundary wall
Contd….
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2.4 Locating the ground 2.4 Locating the ground featuresfeatures
Contd….
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2.5 Chain surveying (field/office 2.5 Chain surveying (field/office work)work)
Equipment Chain/Tape (>30 m) 10 Arrows Raging rods A tape ( 10 m or 20 m ) Cross staff or Optical square Field book, pencil Plumb bob Pegs, wooden hammer, chalks
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2.5 Field work2.5 Field work
Field work consists of three steps Reconnaissance Marking and fixing survey stations Running survey lines
Reconnaissance Walkover survey with the view of principle of
surveying Reference sketch Thinking of possible problem and their solution
in actual survey
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2.5 Field work2.5 Field work
Purpose is to enable to locate stations during progress of work
Wooden pegs in soft ground
Nails or spikes in hard surface (road) & flushed with pavement
For a long time used station, a stone of standard size fixed with mortar
Reference of two or three permanent object
Chaupari
Building
Electric pole
9.65m
10.50m
9.90m
Contd….
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2.5 Field work2.5 Field work
Start chaining from base lineConsists of two folds Chain the survey line Locate the adjacent details
Building
Chaupari
One tape length
Contd….
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2.5 Field work2.5 Field workContd….
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2.5 Office work2.5 Office work
Part of office work
Computation of data
Plotting work Size of paper should be
standard (in mm) A0 = 840 * 1188 A1 = 594 * 840 A2 = 594 * 420 A3 = 420 * 297 A4 = 297 * 210
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2.5 Plotting work2.5 Plotting work
Fix the scale of survey before starting Purpose of survey Extent of survey Finance available
North upward rule
Nice lettering (Always in the drawing)
Skeleton first then offsets Use of tracing paper for proper
orientation
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2.5 Plotting work2.5 Plotting work
Start with base line
Triangles are laid by intersection of arcs
Verification of check lines
Offsets are then plotted by Set square or Offset scale
Ground features representation with symbol
Title box and legend box
Use of HB, 2H and 3H pencils
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Conventional symbols Conventional symbols
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Conventional symbols Conventional symbols Contd….
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