CHAIN SURVEY - Civil Engineering psc short notes

CHAIN SURVEY

•Mainly used in surveying small flat ground 

INSTRUMENTS USED IN CHAIN SURVEYING 


I.   CHAIN 
II.   TAPE 
III.  RANGING ROD 
IV.  RANGING POLE 
V.  ARROWS 
VI.  PEG 
VII.  CROSS STAFF 
VIII.  PLUMBOB 
IX.  OFFSET ROD 
X.  LATHES AND WHITES


1.  CHAIN

•Made of galvanized mild steel wires of 4mm thick 
•2 brass handles connected to chain with swivel joint – to prevent twisting ( bolt used : eye bolt ) 
•Groove is provided at the outer edge for holding arrows. Measurements are taken between the outer edges 
•Degree of accuracy is 1 in 1000 

TYPES OF CHAIN

I.METRIC CHAINS

•Available in 5,10,20,30 
•1 link – 20 cm 
•Brass rings in each 1 meter 
•Tallies in each 5 meter

TOLLERANCE PERMITTED 
  • 1m ± 2mm
  • 5m ± 3mm
  • 20m ± 5mm
  • 30m ± 8mm

PERMISSIBLE ERROR

  • Rough / hilly – 1 in 250
  • Average ground – 1 in 500
  • Level ground – 1 in 1000

NON METRIC CHAINS 

1.ENGINEERS CHAIN

•100 ft long 
•100 links 
•1 link - 1 feet 
•Brass rings in 10 ft each

2.GUNTERS CHAIN / SURVEYORS CHAIN

•66ft long
•100 links
•1 link – 0.66ft 
•10 gunters chain – 1 furlong
•8 furlong /80 gunters chain – 1 mile
•10 square chain – 1 acre

3.REVENUE CHAIN
•33 ft long
•16 links 
•1 link – (33/16) feet

TAPES 

Types : 

I.INVAR TAPE 

•Steel (64%) , nickel (36%) 
•Most accurate 
•Accuracy 1 in 10000 
•Coefficient of linear expansion - (1/30) that of steel – 0.9 x 10 ^(-6) /*c 
•6 mm wide 

II.STEEL TAPE 
•Accuracy 1 in 1000 
•Mainly used for vertical measurements 
•6-10 mm wide 

III.CLOTH / LINEN 
•Made of linen 
•Affected by moisture 
•12 – 15 mm wide 

IV.METTALIC TAPE 
•Linen wound by brass, copper, bronze wire 
•16 mm wide


RANGING ROD 

•2 – 3 m height 
•3 cm diameter 
•Strips – 20 cm 
•If length to be measured >200 m a flag is attached 

RANGING POLE 

•Height 4 - 5 mm 
•Diameter 6 - 10 cm 

ARROWS / MARKING PIN / CHAINING PIN 

• 4mm thick 
•Height 40 ± 5 
•4 cm should be above the ground level 
•Used to mark the end points 
•10 arrows are provided with chain

PEG 

•Height 15 cm of that 4 cm should be above the ground 
•Cross section 25 x 25 
•Used to mark station point , terminal point


INSTRUMENTS FOR SETTING OUT 90° 

I.CROSS STAFF 

1.OPEN CROSS STAFF 

•Only 90 degree angles can be taken 
•Has 2 pair of vertical slits 

2.FRENCH CROSS STAFF 

•Can measure both 45 and 90 degree 
•Hollow octagonal box 
•Distance between 2 slits 8 cm 

3.ADJUSTABLE CROSS STAFF 

•Has 2 cylinders of equal diameter placed on top of each other 
•Can set out any angle


II.OPTICAL SQUARE 

•Only 90 degree can be set out 
•Horizon mirror partially glazed 
•Index mirror – fully glazed 


III.PRISM SQUARE 

•Modern & precise 
•A pentaprism is used 


IV.SIGHT SQUARE 

•2 telescopes placed 90 * to each other 


PLUM BOB 

•Transfer point to the ground 


OFFSET ROD 


•Used to measure small offsets 
•Height 3 m 
•Notch is provided at the top 

PRINCIPLE OF CHAINING 

•Principle of chaining is triangulation 
•Area to be surveyed is divided into triangles - well conditioned triangle ( angles not less than 30* , not greater 120*) 
•Best conditioned triangle - equilateral 
•Chainman at the front - leader , rear - follower 

Duties of the leader : 
•To drag the chain forward 
•To obey instructions of the follower 
•To insert the arrows at the every chain length 

Duties of Follower 
•To place the leader in line with the ranging rod at the forward station. 
•To call out the instructions to the leader 
•Always carry the rear handle of the chain 
•To pick up the arrows inserted by the leader 


TERMS IN CHAINING 

MAIN STATIONS 

•Located at beginning and end of survey lines 
•Forms the main skeleton 
•Lines connecting main stations - MAIN LINES 

SUBSIDIARY / TIE STATIONS 

• stations selected on main lines 
•Function - locating interior details 
•Lines connecting tie stations - TIE LINES - to reduce length of long offset 

BASE LINE : longest chain line used in survey , most important and accurate 

CHECK LINE 

•a line joining main station (apex of triangle) and some fixed point on opp. Side 
•All tie lines are check lines but all check lines are not tie lines 
•Used to check accuracy of the framework 

FIELD BOOK ( size : 20 cm x 12 cm ) - book in which chain / tape measurements are noted 
1.Single line : used in large scare / detailed work , has a central red line representing chain length 
2.Double line : ordinary work , has 2 blue lines , space between line used to note chainage 


ERRORS IN SURVEYING 


SOURCES OF ERRORS 


Instrumental errors - faulty instrument 

Personal errors 

Natural errors 


TYPE OF ERRORS 


1.SYSTEMATIC / CUMULATIVE ERROR ∝ L 

•The cumulative errors are those which occur in the same direction and tend to add up or accumulate 
1.POSITIVE ERRORS: The measured length is more than the actual length. 
2.NEGATIVE ERRORS : The measured lengths less than the actual the length. 

2.COMPENSATING ERRORS / ACCIDENTAL ERROR ∝ √ L 

•The compensating errors are those which occur in either direction and hence tend to compensate. 
•Theory of probability is applied 


ERRORS IN CHAINING 

1.LENGTH OF CHAIN 
•Chain elongated : error -ve , correction +ve 
•Chain shortened : error +ve correction -ve 
• 
2.BAD RANGING 
•Error +ve correction -ve 

3.BAD SIGHTING 
•Error +ve correction -ve 

4.NON HORIZONTALITY OF CHAIN 
•Error +ve correction -ve 

5.VARIATION IN PULL 

6. VARIATION IN TEMPERATURE 
•If temperature greater than 20* c chain elongates, Error +ve correction -ve 
•If temperature less than 20* c chain shrinks, Error -ve correction +ve 

7. SAG IN CHAIN 
•Error +ve correction -ve 


RANGING 

•It is operation of establishing the intermediate points on a given straight line between two terminal stations 

1.DIRECT RANGING : 

•When the two end stations are mutually visible. 
•The minimum number of ranging rod required for direct ranging is 3. 

I.USING EYE RANGER : 3 ranging rods required 
II.USING LINE RANGER : 2 ranging rods required 
III.USING THEODOLITE : 2 ranging rods , aka lining in method 

2.INDIRECT RANGING 

•When the two end stations are not mutually visible 
•The minimum number of ranging rod required for indirect ranging is 4 

I.RECIPROCAL RANGING : 
•2 ends visible from an intermediate point 
•4 ranging rods required, used in case of hillock 

II.RANDOM LINE METHOD 
•2 ends not visible from any intermediate point 

III.USING THEODOLITE 
•Aka balancing in method 
•Both end visible from intermediate point


VIDEO BELOW ARE ALL THE PREVIOUS YEAR REPEATED QUESTIONS  FROM CHAIN SURVEY


4 VIDEOS - 70 PREVIOUS YEAR QUESTIONS 


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