Practical 12 - Object is to determine the Reduced Level of existing road (Profile levelling) PDF

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Practical # 12Object:To determine the Reduced Level of existing road (Profile levelling) (with Height of Instrument Method).Theory:Leveling is the process used to determine a difference in elevation between two points in the vertical plane.The Height of Instrument Method of leveling uses the height ...

Description

Practical # 12 Object: To determine the Reduced Level of existing road (Profile levelling) Height of Instrument Method).

(with

Theory: Leveling is the process used to determine a difference in elevation between two points in the vertical plane.

The Height of Instrument Method of leveling uses the height of instrument to find the reduced levels of road. The reduced level of a station, often called the elevation or height, is the vertical distance between the station and the permanent bench mark. The reduced levels of the stations determine the actual heights of different points on the field. In case of profile leveling of a road, the level of road can be determined at different points by reading the road profile level. After knowing the reduced levels of different points on the road, the profile of road can be obtained which can be used for different purposes.

Instruments required: 1. 2. 3. 4. 5.

Rope (150m) Auto Level Tripod stand Staff rod Chalk (for marking)

Procedure:

1. Place the staff over a bench mark (BM), whose reduced level is known, and set up the Auto Level in convenient and safe location where BM (station A) is visible. Take the staff reading, known as Back sight (B.S). 2. Place the staff over station B. Take the staff reading, known as Intermediate sight (I.S). 3. Repeat step 2 for the stations C and D. 4. Take the last reading over the station E for this position, known as Fore sight (F.S). 5. Now, move the instrument to a new position (position 2) and take the reading on the previous position of the staff (over E). This position of staff is known as Change point (C.P) or Turning point (T.P) and this reading will be Back sight (B.S). 6. Shift the staff over station F. Take the staff reading i.e. I.S. 7. Repeat step 6 for the stations G and H. 8. Take the last reading i.e. F.S over the station I for this position. 9. Now, move the instrument again to a new position (position 3) and take the reading on the previous position of the staff (over I). This will be the second C.P. 10. Shift the staff over station J. Take the staff reading i.e. I.S. 11. Take the last reading i.e. F.S over the station K for this position. 12. Now, move the instrument again to a new position (position 3) and take the reading on the previous position of the staff (over K). This will be the third C.P. 13. Shift the staff over station L. Take the staff reading i.e. I.S. 14. Repeat step 6 for the stations M, N and O.

15. Take the last reading i.e. F.S over the station P for this position. Results: Station

Distance (m)

B.S (m)

A B C D

0 10 20 30

1.65

E F G

40 50 60

1.92

H I J

70 80 90

K L

100 110

M N O

120 130 140

P Sum

150

I.S (m)

F.S (m)

1.61 1.52 1.35

H.I (m)

101.65

1.18 1.78 1.62

102.39

1.46 1.62

1.32 1.45

1.92

102.69

1.32

7.11

103.29

0.85 4.67

100 100.04 100.13 100.3

B.M

100.47 100.61 100.77

C.P1

100.93 101.07 101.24 101.37 101.55

1.74 1.53 1.31 1.07

Reduced level Remarks (m)

101.76 101.98 102.22 102.44

Formulae for calculations:  Height of Instrument (H.I) = Known R.L at B.M/C.P + B.S  Reduced Level = H.I – I.S/F.S Applying Check: ∑B.S - ∑F.S = Last R.L – First R.L 7.11 – 4.67 = 102.44 - 100 2.44 = 2.44 (Check) Graphical Representation of Results:

C.P2 C.P3

Observation in the field:...