QUESTION : EXPLAIN BASIC RULES IN PRACTICE WHEN CONDUCTING A LEVELING

1.     EXPLAIN BASIC RULES IN PRACTICE WHEN CONDUCTING A LEVELING

    

                Levelling is the process of measuring the difference in elevation between two or more points. In engineering surveying, levelling has many application and is used at all stages in construction projects from the initial site survey through the final setting out. In practice, it is possible to measure heights to better than a few millimeters when levelling  this precision  is more than adequate for height measurement on the majority of civil engineering project.

The basic rules in practice when conducting a levelling fieldwork should be adhered to if many of the sources of error are to be avoided. Levelling should always start and finish  at points of known reduced level so that misclosures can be detected. When only one bench mark is available, levelling lines must be run in loops starting and finishing at the bench mark. 

Where possible, all sights length should below 50m. The staff must be held vertically by suitable use of a circular bubble or by rocking the staff and notong the minimum reading. Backsight and fortsight length should be equal for each instrument position. For engineering application, many intermediate sight readings may be taken from each set- up. Under this circumstances it is important that the level has no more than a small collimation error. 

Reading should book immediately after they are observed and important readings, particularly at change points, should be checked. The rise and fall method of reduction should used when heighting reference or change  points and the HPR method ( height of collimation) should be used for contouring , sectioning and setting out applications.