Leveling

Leveling :

• Find the elevation of given points with reference to a given or assumed datum, and
• Establish points to a given elevation or assumed datum
• Establish points at a given elevation or at different elevations with reference to a given or assumed datum.
• Deals with angular and linear measurements in a vertical plane

Fundamental Definition:

Level surface : A curved surface which at each point is perpendicular to the direction of gravity at the point. The surface of a still water is a truly level surface. Any surface  parallel to the mean spheroid surface of the earth is, therefore, a level surface.

Level line: Normal to the plumb line at all points.

Horizontal plane: Tangential  the level surface at the point.

Horizontal line: Straight line tangential to the level at a point. 

Vertical line: Line normal to the level line at a point

Datum: Any surface to which elevations are referred.

Elevation: Vertical distance above or, below an arbitrarily assumed level surface or datum.

Bench Mark: Relatively permanent point of reference whose elevations with reference to

some assume datum known. Used either as a starting point for leveling or as a point upon which to close as a check.

Methods of leveling : Three methods:

Barometric leveling : Makes use of the phenomenon that difference in elevations

between two points is proportional to the difference in atmospheric pressures at these points.

Trigonometric leveling : (Indirect leveling) : In a modified form called Stadia leveling. This method is commonly used in mapping .

Spirit leveling (direct leveling): In this a spirit level and sighting device (telescope)

are combined and vertical distances are measured by observing an graduated rods placed on the points. It is the most precise method.

Commonly used leveling instruments:

• Level
• A leveling staff

Level: is to provide a horizontal line of sight. 

It consists of Four parts.

• A telescope to provide line of sight.
• A level tube to make the line of sight horizontal.
• A leveling head to bring the bubble in its centre of run
•  A tripod to support the Instrument. .

 Chief types of levels are: 

•  Dumpy 
• Wye or Y
• Reversible and  
• Tilting.  

Dumpy Level: The name originated from the fact that formerly this level was equipped with an inverting eyepiece and hence was  shorter then way level of the same magnifying power.

Advantages:

• Simpler construction with fewer movable parts
• Fewer adjustment to be made
• Longer life of the adjustments.

Eye Level: The essential difference between the dumpy level and the way level is that in the former case the telescope is fixed to the spindle while in the way level ,the telescope is carried in two vertical "wye "supports.

The wye level has an advantages over the dumpy level in the fact that the adjustments can be tested with greater rapidity and case.

Reversible Level: Combines  the features  of both the dumpy level and the wye level.

Tilting level: In this the line of sight and the vertical axis need not be exactly perpendicular to each other. It helps in quick leveling.

A Tilting Level is mainly designed for precise leveling work.