1 25 November 08 Unit 2 :Chain Surveying Unit 2: Chain Surveying Unit 2: Chain Surveying.

25 November 08 Unit 2 :Chain Surveying 1

Unit 2: Chain SurveyingUnit 2: Chain Surveying


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


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


2.1 Linear measurement 2.1 Linear measurement methodsmethods

Methods

Electronic methodsBy optical meansDirect measurements


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


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.


2.1 Instruments for 2.1 Instruments for chaining/tapingchaining/taping

Chain/tape

Arrows

pegs

Ranging rods

Plumb bob

Hand level



Arrows 10 arrows

Contd….

Pegs Station position Terminal points of survey line



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….



Plumb bob Verticality of ranging pole Transferring the points to ground Also used for centring purpose in

other surveying methods.

Contd….


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)


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


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


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


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


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



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….



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)


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


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


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


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….



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….



Contd….


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


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



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….



Start chaining from base lineConsists of two folds Chain the survey line Locate the adjacent details

Building

Chaupari

One tape length

Contd….


2.5 Field work2.5 Field workContd….


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


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


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


Conventional symbols Conventional symbols


Conventional symbols Conventional symbols Contd….


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1 25 November 08 Unit 2 :Chain Surveying Unit 2: Chain Surveying Unit 2: Chain Surveying.

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