levelling measurment for survey Ar ppt.pptx

introduction to surveying and levelling measurement

1. levelling Definition of Leveling Levelling is the process of measuring vertical distances above or below a given reference surface and a point on near or below the earth’s surface . Leveling is used to determine the quantity of earthwork in construction works. 14 October 2024 prepared By:Mulugeta Y 1

2. Levelling instruments Levels Levels are categorized in to three groups. Dumpy level Tilting level Automatic levels 2. Tripods A tripod is a three- legged stand used to support a level or other surveying instrument during field measurements. (1) The extension leg tripod and (2) The fixed leg tripod 14 October 2024 prepared By:Mulugeta Y 2

3. 3 . Level rods (leveling staff) They are used to measure the vertical distance between a line of sight and a survey point and a height different between two points. 14 October 2024 prepared By:Mulugeta Y 3

4. Basic Definition and terms used in direct leveling Basic Definitions A vertical line : is the line parallel to the direction of gravity A level surface : is a surface of constant elevation that is perpendicular to a plumb line at every point A level line : is a curved line in a level surface all points of which are of equal elevation Horizontal line : line in horizontal plane, perpendicular to local vertical 14 October 2024 prepared By:Mulugeta Y 4

5. Terms Station : The station is the point where the rod level is held for taking reading (observation) from a leveling instrument. Height of the instrument (H.I ): It is the elevation of the line of sight with respect to the datum Back sight (B.S.): It is the reading taken on a staff held at point of known elevation or at the point whose elevation has already been determined. 14 October 2024 prepared By:Mulugeta Y 5

6. ……..cont’ Fore sight (F.S.): It is the reading taken on the staff either held at the last point whose elevation is required or held at the turning point just before shifting the instrument. Turning point (T.P.): For leveling over a long distance, the instrument has to be set up a number of times. A turning point is the point selected on the route before shifting the instrument. The turning point should be selected on a firm ground or rock. Intermediate sight (I.S.): It is the reading taken on a staff held at point whose elevations is required, but which is not a turning point or the last point. Balancing of sight : To reduce the effect of instrumental and other errors, the distance of the point where a back sight is taken and the distance of the point where a fore sight is taken, as measured from the instrument station, should be approximately equal. This is known as balancing of sights. 14 October 2024 prepared By:Mulugeta Y 6

7. Methods of leveling Direct leveling Differential leveling Profile leveling Cross sectional leveling Reciprocal leveling Indirect leveling Trigonometric Leveling 14 October 2024 prepared By:Mulugeta Y 7

8. Differential leveling Differential leveling is used to determine the elevation difference b/n points some distance apart. It requires a number of instrument set ups along a given route. According to it’s route the leveling procedure can be classify as: Closed – Link Leveling Closed – Loop Leveling 14 October 2024 prepared By:Mulugeta Y 8

9. 14 October 2024 prepared By:Mulugeta Y 9 Closed-link leveling Closed-loop leveling

10. According to the distance between the leveling points the differential level could be: Simple Differential Leveling: When the point is so closed that only one leveling station is required . Compound Differential Leveling: When the distance between the leveling points is so far that several leveling stations are required. 14 October 2024 prepared By:Mulugeta Y 10

11. Example 14 October 2024 prepared By:Mulugeta Y 11

12. Example 14 October 2024 prepared By:Mulugeta Y 12 ∑ BS - ∑FS = ∑ Δ Z Final Elevation – First Elevation =∑ Δ Z

13. Steps of closed-Loop levelling Adjustment 1. Determine the closure error 2. Determine the permissible error (k is the total distance of the levelling route expressed in km) 3. Comparing with and the condition , otherwise the field work has to be repeated   14 October 2024 prepared By:Mulugeta Y 13

14. 4. Compute the correction 5. Apply the correction to each The correction should be the appositive sign of the error When all ∆z are corrected it fulfilled that: 6. Compute the elevation of points   14 October 2024 prepared By:Mulugeta Y 14

15. Example 14 October 2024 prepared By:Mulugeta Y 15

16. Filling out the calculation sheet 14 October 2024 prepared By:Mulugeta Y 16

17. Solution:   14 October 2024 prepared By:Mulugeta Y 17

18.   14 October 2024 prepared By:Mulugeta Y 18

19. 5. Apply the correction to each ∆z ∆ z 1(corrected) = - 1.254 – 0.003 = - 1.257  ∆z 2(corrected) = +2.324 – 0.002 = +2 . 322  ∆z 3(corrected) = +1.592 – 0.002 = +1.590 ∆z 4(corrected) = - 1.345 – 0.004 = - 1.349 ∆z 5(corrected) = - 1.302 – 0.004 = - 1.306 ∑ ∆z = 0 14 October 2024 prepared By:Mulugeta Y 19

20. 6. Compute the elevation of points Elev( unknown point ) = Elev ( known point ) ± ∆z Elev(A) = Elev ( BM) ± ∆z=100 - 1.257 = 98.743 Elev(B) = Elev(A) ± ∆z= 98.743 + 2.322 = 101.065 Elev(C) = Elev(B) ± ∆z= 101.065 + 1.590 = 102. 655 Elev(D) = Elev(C) ± ∆z= 102.655 – 1.349 = 101.306 For check up Elev(BM) = Elev(D) ± ∆z= 101. 306 – 1.306 = 100.00 OK 14 October 2024 prepared By:Mulugeta Y 20