LEVELLING AND CONTOURING 1 LEVELLING According to science

LEVELLING AND CONTOURING 1

LEVELLING ü According to science • Leveling is a branch of surveying which deals with the measurement of relative heights of different points on, above or below the surface of the earth. Thus in leveling, the measurements (elevations) are taken in the vertical plane. ü Simple Definition • Leveling is the process used to determine a difference in elevation between two points. LEVELLING 2

DEFINITIONS Definitions • Station: - A point where the levelling staff is kept. • Height of instrument: - It is the elevation of the plane of sight with respect to assumed datum. It is also known as plane of collimation. • Datum line ( M. S. L. ) : - Is the level (line) which are attributed to it points levels on the surface of the Earth. Which is the average sea level. • Reduced level ( R. L) : - Is the high point from datum line. • Benchmark (B. M ) : - Are fixed points information site and attributed placed in different places until you start racing them when conducting settlement. • Back sight ( B. S. ) : - Is the first reading taken after placing the device in any position so that we see the greatest possible number of points required to find the elevation. LEVELLING 3

DEFINITIONS • BENCHMARKS LEVELLING 4

DEFINITIONS • Fore sight (F. S) : - Is the last reading taken before the transfer device. • Change point(CP) or turning point(TP): The point at which both BS and FS are taken. • Intermediate sight ( I. S. ) : - Is reading taken between the back sight and fore sight reading. • Elevation of line of sight ( H. I) : - Is the imaginary vertical level determined by the line of sight to the amount of increase or decrease for sea level. LEVELLING 5

DEFINITIONS • Tripod stand : - is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. TRIPOD STAND LEVELLING PLUMB BOB TRIPOD STAND 6

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DEFINITIONS • Leveling Staff : -Is a wooden or metal ruler one side runway to meters and centimeters. And is a ruler of solid wood 2 , 3 , 4 , 5 meters in length and usually 4 meters. LEVELLING 8

LEVELING OF THE INSTRUMENT • Leveling of the instrument is done to make the vertical axis of the instrument truly vertical. It is achieved by carrying out the following steps: • Step 1: The level tube is brought parallel to any two of the foot screws, by rotating the upper part of the instrument. • Step 2: The bubble is brought to the centre of the level tube by rotating both the foot screws either inward or outward. (The bubble moves in the same direction as the left thumb. ) • Step 3: The level tube is then brought over the third foot screw again by rotating the upper part of the instrument. • Step 4: The bubble is then again brought to the centre of the level tube by rotating the third foot screw either inward or outward. LEVELLING 9

LEVELING OF THE INSTRUMENT • Step 5: By rotating the upper part of the instrument through 180 ° , the level tube is brought parallel to first two foot screws in reverse order. The bubble will remain in the centre if the instrument is in permanent adjustment. LEVELLING 10

TYPES OF LEVELLING 1] Simple levelling 2] Differential levelling 3] Fly levelling 4] Profile levelling 5] Cross sectional levelling 6] Reciprocal levelling There are two methods for obtaining the elevations at different points: 1] Height of instrument (or plane of collimation) method 2] Rise and fall method LEVELLING 11

TYPES OF LEVELLING Simple levelling: • When the difference in the elevation of two nearby points is required then simple levelling is performed. LEVELLING 12

TYPES OF LEVELLING Differential levelling: • Performed when the final point is very far from the final point. LEVELLING 13

TYPES OF LEVELLING Fly levelling • Performed when the work site is very far away from the bench mark. • The surveyor starts by taking BS at BM and proceed towards worksite till he finds a suitable place for temporary BM. All works are done with respect to temporary BM. • At the end of the day the surveyor comes back to original BM. • This is called fly levelling. LEVELLING 14

TYPES OF LEVELLING Profile levelling: - • Profile levelling, which yields elevations at definite points along a reference line, provides the needed data for designing facilities such as highways, railroads, transmission lines. • Reduced levels at various points at regular interval along the line is calculated. • After getting the RL of various points the profile is drawn. Normally vertical scale is much larger than horizontal scale for the clear view of the profile. LEVELLING 15

TYPES OF LEVELLING Reciprocal levelling: When levelling across river is required then this method is applied to get rid of various errors. LEVELLING 16

METHODS OF LEVELLING METHODS 1] Height of Instrument method • The basic equations are • Height of instrument for the first setting= RL of BM + BS(at BM) • Subtract the IS and FS from HI to get RL of intermediate stations and change points. • Checking: ΣBS -ΣFS = Last RL –First RL. This is –ve for FALL and +ve for RISE. LEVELLING 17

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METHODS OF LEVELLING METHODS 2] Rise and Fall method • In this method the difference of the present staff reading is subtracted from the previous staff reading. • Previous reading –present staff reading = +ve, denotes RISE • Previous reading –present staff reading = -ve, denotes FALL • Checking: ΣBS -ΣFS = Last RL –First RL= ΣRise -ΣFall LEVELLING 19

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CONCEPT FIND THE DIFFERENT BETWEEN BENCH MARK AND TOP OF SLOPE Rotate dumpy round Back sight 9 m BENCH MARK ELEVATED e. g. 100 m LEVELLING Back sight 6 m Fore sight 2 m Fore sight 1 m TOP OF SLOPE Divide hill into 3 spots to make easier Otherwise too far to see or level staff not long enough Move level staff to new spot Move dumpy level to new spot Move level staff to new spot 21 ?

CONCEPT Level of dumpy=113 m Fore sight 1 m Level of dumpy=109 m Fore sight 2 m Back sight 9 m 9 m 100 m+ 9 m Back sight 6 m 6 m+107 m 6 m 2 m SO THE DIFFERENCE IN HEIGHT IS BENCH MARK ELEVATED e. g. 100 m Ground Back sight level [from dumpy level] 1 m Height of instrument [ground level+ back sight from dumpy level] 112 -100=12 M Fore sight [from dumpy level] Height of new point [height of instrument fore sight] 22

CONTOURING 23

CONTOURS • Contours are those lines you can see on OS maps. • A contour line is an imaginary line that joins points of equal height above sea level. • They can be used to learn about the shape of the land (the relief). • A map with only a few contour lines will be flat (and often low lying) • If a map has lots of contours it is a mountainous or hilly area. • The actual pattern of the lines will tell you more detail about the area too. CONTOURS Area that is flatter with only a gentle slope Steep slopes 24

CONTOURS • Contour An imaginary line on the ground surface joining the points of equal elevation is known as contour. • In other words, contour is a line in which the ground surface is intersected by a level surface obtained by joining points of equal elevation. This line on the map represents a contour and is called contour line. • Contour Map : -A map showing contour lines is known as Contour map. • A contour map gives an idea of the altitudes of the surface features as well as their relative positions in plan serves the purpose of both, a plan and a section. CONTOURS 25

CONTOURING Contouring • The process of tracing contour lines on the surface of the earth is called Contouring. • PURPOSE OF CONTOURING • Contour survey is carried out at the starting of any engineering project such as a road, a railway, a canal, a dam, a building etc. eparing contour n. For mapsi) or suitable site. ii) line. alignment mark the To roads quantity railways and the iii) that ofso of earthwork both in cutting and filling should be minimum. CONTOURS 26

CONTOURING iv) undulating or mountainous. v) especially in a mountainous region. vi) To trace out the given grade of a particular route. vii)To locate the physical features of the ground such as a pond depression, hill, steep or small slopes. CONTOURS 27

METHODS OF CONTOURING • There are mainly two methods of locating contours: (1)Direct Method and (2) Indirect Method. CONTOURS 28

METHODS OF CONTOURING 1] Direct Method: • In this method, the contours to be located are directly traced out in the field by locating and marking a number of points on each contour. • These points are then surveyed and plotted on plan and the contours drawn through them. • This method is most accurate but very slow and tedious as a lot of time is wasted in searching points of the same elevation for a contour. • This is suitable for small area and where great accuracy is required CONTOURS B. M. 50 48 46 DIRECT METHOD OF CONTOURING 29

METHODS OF CONTOURING Procedure: • To start with, a temporary B. M is established near the area to be surveyed with reference to a permanent B. M by fly levelling. • The level is then set up in such a position so that the maximum number of points can be commanded from the instrument station. • The height of instrument is determined by taking a back sight on the B. M. and adding it to the R. L. of bench mark. • The staff reading required to fix points on the various contours is determined by subtracting the R. L. of each of the contours from the height of instrument. CONTOURS 30

METHODS OF CONTOURING • Example: • If the height of instrument is 82. 48 m. , then the staff readings required to locate 82, 81 and 80 m contours are 0. 48, 1. 48 and 2. 48 m respectively. The staff is held on an approximate position of point and then moved up and down the slope until the desired reading is obtained. The point is marked with a peg. • Similarly various other points are marked on each contour. The line joining all these points give the required contour. It may be noted that one contour is located at a time. Having fixed the contours within the range of the instrument, the level is shifted and set up in a new position. CONTOURS 31

METHODS OF CONTOURING Procedure (Contd…. . ) • The new height of instrument and the required staff readings are then calculated in a similar manner and the process repeated till all the contours are located. • The positions of the contour points are located suitably either simultaneous with levelling or afterwards. • A theodolite , a compass or a plane table traversing is usually adopted for locating these points. • The points are then plotted on the plan and the contours drawn by joining the corresponding points by dotted curved lines. CONTOURS 32

METHODS OF CONTOURING Direct Method By Radial Lines • This method is suitable for small areas, where a single point in the centre can command the whole area. Radial lines are laid out from the common centre by theodolite or compass and their positions are fixed up by horizontal angles and bearings. 70 65 60 55 RADIAL LINES METHOD OF CONTOURING CONTOURS 33

METHODS OF CONTOURING Direct Method By Radial Lines (contd. ): • Temporary bench marks are first established at the centre and near the ends of the radial lines. • The contour points are then located and marked on these lines and their positions are determined by measuring their distances along the radial lines. • They are then plotted on the plan and the contours drawn by joining all the corresponding points with the help of a plane table instrument. CONTOURS 34

METHODS OF CONTOURING 2. INDIRECT METHOD • In this method the points located and surveyed are not necessarily on the contour lines but the spot levels are taken along the series of lines laid out over the area. • The spot levels of the several representative points representing hills, depressions, ridge and valley lines and the changes in the slope all over the area to be contoured are also observed. • Their positions are then plotted on the plan and the contours drawn by interpolation. • This method of contouring is also known as contouring by spot levels. CONTOURS 35

METHODS OF CONTOURING • This method is commonly employed in all kinds of surveys as this is cheaper, quicker and less tedious as compared to direct method. There are mainly three method of contouring in indirect method: • (I) BY SQUARES [SQUARE METHOD]: • In this method, the whole area is divided into number of squares, the side of which may vary from 5 m to 30 m depending upon the nature of the ground and the contour interval. The square need not be of the same size throughout. • The corners of the squares are pegged out and the reduced levels of these points are determined with a level. CONTOURS 36

METHODS OF CONTOURING SQUARE METHOD CONTOURS 37

METHODS OF CONTOURING (II) By Cross- Sections: • This method is most suitable for the survey of long narrow strips such as a road, railway or canal etc. CONTOURS 38

METHODS OF CONTOURING • (III) By Tacheometric method: • A techeometer is a transit theodolite having a diaphragm fitted with two stadia wires, one above and other below the central wire. • The horizontal distance between the instrument and staff station may be determined by multiplying the difference of the staff readings of the upper and lower stadia wires with the stadia constant of the instrument, which is usually 100. • Thus the techeometer is used for both the vertical as well as horizontal measurements. CONTOURS Stadia Wires at Diaphragm 39

METHODS OF CONTOURING iii) By Tacheometric method (contd…): • This method is most suitable in hilly areas as the number of stations which can be commanded by a techeometer is far more than those by a level and thus the number of instrument settings are considerably reduced. A number of radial lines are laid out at a known angular interval and representative points are marked by pegs along these radial lines. Their elevations and distances are then calculated and plotted on the plan and the contour lines are then interpolated. CONTOURS 40

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