SURVEYING I

CENG 383

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Introduction Definition An art of collecting data for mapping

the relative positions of points above, below or on the surface of the earth.

Surveying also includes the art of locating or setting out points on the ground from a plan or a map.

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Continued … • Surveying involves the measurement of distances

and angles for one or more of the following purposes:

1. To determine the relative positions of points on the earth’s surface – to locate arbitrary points, configuration of the ground, direction and length of lines, boundary lines, etc,

2. To set out the line and grades needed for the construction of structures.

3. To calculate areas, volumes and other related quantities.

4. To prepare necessary maps and diagrams of an area.

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Continued … • Application • Surveying is being used: -

– In developing databases for natural resource management. – In establishing boundaries of public and private lands

– In preparing navigational maps (land, air, water). – To map the earth above and below the sea. – In geological and geophysical studies

– In planning, design, construction, erection, renovation and maintenance of engineering works

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Classification of surveying

I. Engineering Surveying

II.Geodetic Surveying

III.Plane Surveying

IV.Miscellaneous Survey

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Engineering Surveying • Is the surveys which are carried

out with some engineering consideration

• Further classified as: 1. Reconnaissance survey 2. Preliminary survey 3. Location survey

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Continued .. 1. Reconnaissance survey - is the first engineering survey - is carried out to study the details of the proposed

project or scheme. * 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

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Continued … 2. Preliminary survey • The objective 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 routs and to decide which route will be the most economical.

• It should be carried out with great precision

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Continued … 3. Location survey

* The main objective of location survey is to carry out the detailed survey along the route which has been found and fixed as the most economical route from the data of the preliminary survey.

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Geodetic Surveys • Is also called the trigonometrical

surveying as it involves spherical trigonometry.

• The spherical shape of the earth is considered.

• The geodetic surveys ensure with the great precision the precise positions of the stations on the surface of the earth.

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Plane Surveys • In this type of surveying, the curvature of the

earth is not considered and the surface of the earth is treated as a plane surface.

• The assumption to treat the surface of the earth as plane surface can also be justified on the following two ground:

1. For an area of about 195km2 on earth’s surface, the difference b/n the sum of angles of a spherical triangle and the corresponding plane triangle is only one second.

2. The difference b/n the arc and the subtended chord on the surface of the earth of length 91km is only about 50cm.

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Continued … • Plane surveys can be subdivided into two broad

categories as follows: 1. Depending up on the shape of framework i. Triangulation ii. Traversing 2. Depending upon the type of instruments employed. i. Chain survey iv. Photographic and areal survey. ii. Compass survey v. Tacheometric survey iii. Plane table survey vi. Theodolite survey

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Miscellaneous survey 1. Archaeological Surveys 2. Astronomical Survey 3. Cadastral Survey or Land survey 4. City Survey 5. Geological Surveys 6. Marin Surveys 7. Military Surveys 8. Mining Surveys 9. Topographical Surveys 10. Route surveys 11. Hydrographic surveys

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Principles of surveying 1. The survey work should be carried out

from the whole to the part and not from the part to the whole.

2. The length of main lines and the positions of important survey stations should be ascertained by at least two independent measurements.

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Basic Measurements and Instruments Used

• Horizontal distance: – measured by tapes, chains, tacheometers, EDM, pacing, odometer, etc.

• Vertical distance: – measured by levels, tacheometers.

• Horizontal angles: – measured by theodolites, compasses.

• Vertical angles: – measured by theodolites, clinometers.

• Basic units of measurements table

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Continued … • Scales

* The scale of a map or a plan is the ratio of a distance measured on the plan or map to its corresponding distance on the ground. Examples

• Large scales:- < 1:200 • Intermediate scales: - 1:2000 to 1:10,000 • Small scales: - 1:10,000 to 1:100,000,000

– For plans • Site plans: - 1:50 to 1:500 • Detail plans: - 1:1 to 1:20

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Continued … • Map: - the scale is too small to allow every

feature to be properly represented.

• Conventional symbols are used to represent features that would otherwise be too small to be recognized.

• Plan: - on the other hand, shows all features on the ground correctly to scale.

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Surveying Activities • A complete Surveying activity

involves the following steps: -

1. Field operations

2. Office Work

3. Use of instruments

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1. Field operations • Field operation involve

– To determine the relative altitudes of points – To establish stations and bench marks. – To locate the details – To measure distances and angles. – To set out boundary lines and grades for a variety of

construction works such as culvert, bridges, buildings, sewers, waterlines etc.

– To survey contours of the land area, etc. – To carry out miscellaneous notes which would be of

immense help in plotting.

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2. Office work 1. Planning and design of the survey

specification coordinate system and datum, selection of equipment and procedure.

2. Calculations and adjustment of data

3. Preparation of plans, maps, etc.

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3. Use of instruments • Precautions that has to take while using the survey instruments

are as follows: – The lifting and shifting of the instrument should be carried

out with extreme care. – The movable parts and screws of the instrument should not be

tightened with force. But they should be lubricated to have smooth working.

– The instructions supplied by the manufacturer should be lubricated to have smooth working.

– The instrument should be properly taken while starting the work and should be placed back in its original position when the work is over.

– The instrument should be suitably protected from rain, dust, sun, storm, etc.

– The instrument should never be left unguarded. Otherwise it is likely to be damaged by cattle, traffic or blowing wind.

– While placing the instrument on smooth surfaces, care should be taken to see that its legs do not spread out.

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Method of keeping note 1. Written description of what has

been done

2. Using sketch

3. Tabulation of numerical data

4. Combination of the above

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Reference systems 1. Geographic reference system fig 2. Grid reference system - the earth surface is divided in to rectangular grid for

horizontal reference. - Advantages of this system are the ease of calculation

(plane Geometry and trigonometry) and the availability of one common datum for the X and Y dimensions in large area

3. Vertical reference system - A vertical datum is a surface which all elevations and

depths are referred. - the referenced datum most widely used is that of mean

sea level (msl) which is assigned an elevation of 0.000m.