Q1: What is meant by levelling?
Ans:Levelling is the art of determining the relative heights of different points on or below the surface of the earth. Thus, levelling deals with measurements in the vertical plane.
Q2: Define bench mark.
Ans:Bench-marks (BM) are fixed points of known RL determined with reference to the datum line. They serve as reference points for levelling operations.
Q3: Differentiate between G.T.S and permanent bench mark.
Ans: GTS Bench-Marks: Established by the Survey of India at large intervals nationwide.
Permanent Bench-Marks: Fixed by local departments like PWD, Railways, and Irrigation, referenced to a GTS BM.
Q4: What is datum surface?
Ans:A datum surface is an imaginary level surface from which vertical distances of different points are measured. In India, the datum used for GTS is the Mean Sea Level (MSL) at Karachi.
Q5: State the purposes of levelling.
Ans:
The purposes of levelling are:- ➔To prepare contour maps for reservoirs, dams, and roads.
- ➔To determine altitudes of important points.
- ➔To prepare longitudinal and cross-sections for earthwork calculations.
- ➔To prepare layout maps for water supply and drainage schemes.
Q6: Name the types of bench mark.
Ans:
The types are:- ➔GTS Bench-Marks
- ➔Permanent Bench-Marks
- ➔Arbitrary Bench-Marks
- ➔Temporary Bench-Marks
Q7: How is the level centered?
Ans:The level is centered using foot screws to adjust the instrument so that the bubble is in the center of the tube.
Q8: Define Parallax.
Ans:Parallax is the apparent movement of the crosshairs against the staff when the observer moves their eye slightly.
Q9: Define focusing.
Ans:Focusing is the adjustment of the eyepiece and object glass to get a clear image of the staff readings.
Q10: Define line of collimation.
Ans:The line of collimation is an imaginary line passing through the cross-hairs and the optical center of the object glass.
Q11: Name at least six parts of a level.
Ans:
The parts are:- ➔Telescope
- ➔Bubble Tubes
- ➔Levelling Head
- ➔Tripod Stand
- ➔Foot Screws
- ➔Focusing Screw
Q12: Define height of instrument.
Ans:The height of the instrument (HI) is obtained by adding the backsight reading to the RL of the benchmark or change point.
Q13: What are the steps of temporary adjustment of a level?
Ans:
- ➔Approximate levelling by adjusting tripod legs.
- ➔Levelling using foot screws.
- ➔Focusing the eyepiece and object glass.
Q14: How is the check of levelling work done?
Ans:The accuracy of levelling is checked by performing check levelling, which involves fly levelling back to the starting point.
Q15: What is the purpose of fly levelling?
Ans:Fly levelling is done to connect a bench-mark to the starting point of a project or to check accuracy.
Q16: What is the purpose of reciprocal levelling?
Ans:Reciprocal levelling eliminates errors due to curvature and refraction when levelling across a river or valley.
Q17: What is the purpose of profile levelling?
Ans:Profile levelling determines ground undulations along an alignment for road, railway, or canal projects.
Q18: Name the types of levelling.
Ans:
The types are:- ➔Simple Levelling
- ➔Longitudinal Levelling
- ➔Differential Levelling
- ➔Fly Levelling
- ➔Cross-Sectional Levelling
- ➔Check Levelling