Surveying
Surveying
It is field of engineering that deals with spatial information about positions and points on, above or below the earth’s surface.
Purpose of surveying
1) To study the site for its suitability for some engineering work.
2) To determine and measure accurately the relative heights and depths or levels of the various points and features in their relative position.
3) To establish correctly the boundary points of the property from available records.
4) To constitute maps or plans, sections or, profiles,spot levels and contours by plotting the measurements to some scale on paper.
5) To calculate the distance between the various points, levels of various points area and quantities of materials such as earthwork etc.involved for the various engineering projects like railway,canal,road etc.
Classification of surveys
Survey can be classified into four categories
1- Engineering survey
2- Geodetic Survey
3- Plane survey
4- Miscellaneous survey
(1)Engineering survey
This is undertaken for the determination of quantities or to afford sufficient data for the design of engineering works such as roads and reservoirs or those connected with sewage disposal or water supply.
Engineering survey further classified into following groups
i )Location Survey -The main purpose of this Survey is to carry out the detailed survey along the route which has been found and fixed as the most economical route from the date of the preliminary survey.As soon as the location survey is competed , the construction work is started and thus ,the end of location Survey proves to be the starting point of the construction activities of the proposed project or scheme.
ii) Preliminary Survey - The object of preliminary survey is to conduct the survey along the alternative routes found out by the reconnaissance survey and to determine with greater accuracy the cost along these alternative routes and to decide which routes will be the most economical.Thus,the preliminary survey should be carried out with greater precision as on it depends the alignment of the final route.
iii) Reconnaissance Survey -The successful conduct of the reconnaissance survey entirely depends on the personal qualities of the engineer such as his training and experience,his capacity of observation and interpretation of the features of the territory etc.
(2) Geodetic survey
Geodetic survey is the types of surveying in which the shape of the earth is taken into account. All lines lying in the surface are curved lines and the triangles are spherical triangle. It, therefore, involves spherical trigonometry .All geodetic surveys include work of larger magnitude and high degree of precision. these object of geodetic survey is to determine the precise position on the surface of the earth,of a system of widely distant points which form control stations to which surveys of less precision may be reffered.
(3) Plane survey
In this type of surveying surface of earth is considered as a plane and the spherical shape is neglected.All triangle formed by the survey lines are considered as plane triangles .The level line is considered as straight and all plumb lines are considered parallel.
In every day life we are concerned with small portions of earth's surface and the length of arc 12 km long lying in the earth's surface is only 1 cm greater than the subtended chord.and further that the difference between the sum of the angles in a plane triangle and the sum of those in a spherical triangle is only one second for a triangle at the earth's surface having an area of 195 sq.km.
4- Miscellaneous survey
i) Archaeological survey
A systematic attempt to locate , identify and record the distribution, structure and form of archaeological sites on the ground and in relation to their natural geographic and environmental setting.
ii) Astronomical survey
It is a branch of land surveying were position are determined by using celestial bodies e.g stars ,sun etc .
iii) Cadastral survey
To fix the boundary lines of private owners or public bodies and to calculate the enclosed land area.
iv) City survey
This is performed in connection with town planning schemes such as drainage, water supply etc and for laying out plots,roads, streets etc.
v) Geological survey
This is used for determining different strata in the earth's crust.
vi)Marine survey
Marine survey is a independent evaluation of watercraft's value and conditions by a professional marine surveyor.
vii) Military survey
It is the process of obtaining information about the position , activities, resources etc of an enemy in case of war
viii) Mining survey
To expose the hidden wealth of the country such as coal,gold,copper etc.
ix) Topographical survey
This is used for determining the natural features of the country such as lakes,rivers,hills,woods etc.
Principles of surveying
The fundamental principles upon which the various methods of plane surveying are based are of very simple nature and can be stated under the following two aspects:
1) Location of a point by measurement from two point of reference.
2)Working from whole to part
1) Location of a point by measurement from two point of reference.
The relative position of the point to be surveyed should be located by measurement from at least two point of reference, the position of which have already been fixed
2)Working from whole to part
The second principle of surveying, whether plane or geodetic ,is to work from whole to part .It is very essential to establish first a system of control points and to fix them with higher precision.Minor control points can then be established by less precise methods and the details can then be located using these minor control points by running minor traverses.
Scale
The area that is surveyed is vast and , therefore ,plans are made to some scale .
Scale is the fixed ratio that every distance on the plan bears with corresponding distance on the ground .
Types of Scale
Scale may be classified as follows:
1- Plain Scale
2- Diagonal Scale
3- Vernier Scale
4- Scale of chord.
1- Plain Scale
A plain scale is one on which it is possible to measure two dimensions only ,such as unit and tenths, meter and decimetres ,miles and furlongs, etc.
2- Diagonal Scale
On a diagonal scale,it is possible to measure three dimensions such as metres, decimetres and centimetres; units, tenths and hundredths: yard ,feet and inches etc.
3- Vernier Scale
The vernier is a device for measuring the fractional part of one of the smallest divisions of a graduated scale.It usually consists of a small auxiliary scale which slides along side the main scale.
A vernier can primarily be divided into the following two classes:
a)- Direct Vernier
b)- Retrograde Vernier .
4- Scale of chord.
A scale of chords is used to measure an angle or to set-off an angle ,and is marked either on a rectangular protractor or on an ordinary box wood scale.
Basic units of length
|
12 inches |
1 foot |
|
3 feet |
1 yard |
|
4 poles |
1 chain( 66 feet) |
|
10 chain |
1 furlong |
|
8 furlongs |
1 mile |
|
100 links |
1 chain (66 feet) |
|
6 feet |
1 fathom |
|
120 fathoms |
1 cable length |
|
6080 feet |
1 nautical mile |
|
10 milimetres |
1 centimetre |
|
10 centimetres |
1 decimetre |
|
10 decimetres |
1 metre |
|
10 metres |
1 decameter |
|
10 decameter |
1 hectometer |
|
10 hectometer |
1 kilometre |
|
1852 metres |
1 nautical mile |
Present
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