One-liner Surveying - 01
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Surveying
Object of surveying - It is the preparation of plan and map
Plan - Large scale representation of small areas is called plan.
Map - Small scale representation of small areas is called map.
Principal of surveying :-
- To work from whole to the part.
- To locate a new station at least two measurement.
➤ If the curvature of earth is considered then it is called Geodetic surveying (Area > 250 km2).
➤ If the curvature of earth is not considered then it is called Plane surveying (Area < 250 km2).
➤ The difference between the length arch of circle and subtended chord on the surface of earth is 0.1m for 18.2km, 0.3m for 54.3km, 0.5m for 91 km.
➤ Sum of the angles on spherical triangle on the earth surface & corresponding plane triangle is 1 sec per 195.5 Sq. km area. [Building Material]
➤ Plane angle measured in terms of radians.
➤ Spherical triangle is measured in terms of steradians.
Tapes use in Surveying :-
1. Cloth and linen tape - It is available in 10m, 20m, 25m, and 30m length. It is not accurate.
2. Glass fibre tape - These tape are not strech or shrink due to changing temperature and moisture content. It is accurate than cloth tape .
3. Metallic tape - These tapes more durable than glass fibre tape & cloth tape.
4. Steel tape - It is more accurate than metallic tape.
5. Invar tape - It is made up of steel (64%) & nickel (36%). It is more accurate than all other tapes.[Surveying]
Q. Classification of Survey ?➤ Arrow - It is used to indicate position of the end of chain on the ground.
➤ Peg - It is used to indicate position of survey stations or end points of the survey line.
➤ Ranging rod - It is used to locate intermediate points such that these points lie on the straight line joining the end stations. [Concrete Technology]
➤ Ranging - The process of establishing the intermediate points is known as ranging.
Chains used in surveying :-
- Matric Chain - 20 m chain - 100 links - each link 0.2m
- Matric Chain - 30m chain - 150 links - each link 0.2m
- Engineer's chain - 100 ft - 100 links - each link 1 ft
- Revenue chain - 33 ft - 16 links - each link 2.063 ft
- Gunter's chain / Surveyor's chain - 66 ft - 100 links - each link 0.66 ft
Tolerance limit of chains in surveying :-
20 m chain - ± 5mm30 m chain - ±8mm
Error due to wrong scale :-
Correct length = {( RF of wrong scale )/ (RF of correct scale) }* Measured length
Correct area = {( RF of wrong scale )/ (RF of correct scale) }^2* Measured length
Errors due to shrinkage :-
- Shrinkage ratio - Length after shrinkage/actual length.
- Correct distance - measured distance/ shrinkage factor.
- Correct area - Measured area/(shrinkage factor)^2. [Building Material]
Types of map use in surveying :-
- Topographical map - Shows the hills, Valleys, rivers, Village, towns, forests etc.
- Cadastral map - Showing the boundaries of fields, houses & other properties.
- Engineering map - Shows details of engineering works such as roads, railway, reservoirs, irrigation canals etc.
- Geological map - Showing areas including underground resources.
- Contour map - Determine the capacity of reservoir and to find best possible route for roads & railways. [Building Material]
- Military map - showing the road & railway communication with different parts of a country such a map also shows the different strategic points important for the defence of a country.
- Archeological Map - Showing areas including places where ancient relics exist.
Generally used scales in surveying :-
➤ Geographical map - 1 cm = 160 km.
➤ Topographical map - 1 cm = 2.5 km.
➤ Forest map - 1 cm = 0.25 km.
➤ Town planning - 1 cm = 50 m to 100 m.
➤ Cadastral map - 1 cm = 10 m to 50 m.
➤ Location map - 1 cm = 5 m to 25 m. [Building Material]
➤ Mines - 1 cm = 10 m to 25 m.
➤ Buildings - 1 cm = 10 m.
➤ Preliminary survey of rails and roads - 1 cm = 10 m to 60 m.
Technical name of Surveying :-
➽ Survey line - The line joining the main survey stations.
➽ Check line or proof line - The lines used for check the accuracy of the frame work of triangles.
➽ Main stations - Major control points to divide the area called main stations.
➽ Main line - Line joining main stations.
➽ Base line - Longest line in that area divide the almost in two part.
➽ Tie line - Any line drawn to collect more information about different objects in area.
➽ Leader - The chainman at the forward end of the chain, who drags the chain forward is known as leader. [Building Material]
➽ Follower - The chainman at the rear end of the chain, who holds the zero end of the chain at the station is known as follower.
➽ Offset - Lateral distance measured from main survey line.
➽ Perpendicular offset - The short measurement at right angles to the survey line.
➽ Oblique offset - The short measurement inclined to survey line.
➽ Range type offset - It is a Oblique offset taken along the line of wall a building.
➽ Cross staff - Instrument used for setting perpendicular offset.
➽ French cross staff - It is used to set-out perpendicular offset and oblique offset with an angle 45° to 135°.[Concrete Technology]
➽ Adjustable cross staff - It is used to set-out offset with an angle of any magnitude
➽ Optical square - It is used to set-out perpendicular offset more accurate than cross staff. It works under principle of double refraction
➽ Prism square - It is used to set-out perpendicular offset more accurate than optical square
- Maximum length of offset is limited to 15m.
- Walking step of man is 80cm.
Error due to incorrect ranging -
- Error in length (20m chain) - d^2/40
- Error in length (30m chain) - d^2/60
Obstacles in chaining :-
- Chaining around the obstacle is possible e.g pond or lake.
- Chaining around the obstacle is not possible e.g. river.
- Obstacles in ranging e.g. Hills or mountains.
- Obstacles in chaining & ranging e.g Buildings.[Concrete Technology]
The sketch prepared during reconnaissance survey known as Index sketch.
The main survey stations are located on ground by Reference sketch.
A triangle is said to be well conditioned when it's angle should be lie between 30° and 120°
Field book used in surveying :-
~ Standard dimensions of field book is 20 × 21 cm.
~ Double line field book is most commonly used for ordinary survey works where accuracy is less. [Building Material]
~ Single line field book is used for very large scale works where more details are to be entered.
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