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LECTURE №5

LEVELING

5.1 Introduction
Leveling is the general term applied to any of the various processes by which
elevations of points or differences in elevation are determined. It is a vital
operation in producing necessary data for mapping, engineering design, and
construction.
Leveling results are used to:
1. Design highways, railroads, canals, sewers etc.
2. Layout construction projects according to planned elevations.
3. Calculate volume of earthwork and other materials.
4. Investigate drainage characteristics of the area.
5. Develop maps showing ground configuration.

5.2 Measuring Vertical Distances
The vertical direction is parallel to the direction of gravity; at any point, it is the
direction of a freely suspended plumb-bob cord. The vertical distance of a point
above or below a given reference surface is called the elevation of the point. The
most commonly used reference surface for vertical distance is mean sea level. The
vertical distances are measured by the surveyor in order to determine the elevation
of points, in a process called running levels or leveling.
The determination and control of elevations constitute a fundamental operation

in surveying and engineering projects. Leveling provides data for determining the
shape of the ground and drawing topographic maps and the elevation of new
facilities such as roads, structural foundations, and pipelines.

5.3 Methods of Leveling
There are several methods for measuring vertical distances and determining the
elevations of points. Traditional methods include barometric leveling,

trigonometric leveling and differential leveling. Two very advanced and
sophisticated techniques include inertia leveling and global positioning systems.
1. Barometric leveling
By using special barometers to measure air pressure (which decrease with
increasing elevation), the elevation of points on the earth's surface can be
determined within ±1m. This method is useful for doing a reconnaissance survey
of large areas in rough country and for obtaining preliminary topographic data.
2. Differential leveling
By far the most common leveling method, and the one which most surveyors are
concerned with, is differential leveling. It may also be called spirit leveling,
because the basic instrument used comprises a telescopic sight and a sensitive
spirit bubble vial. The spirit bubble vial serves to align the telescopic sight in a
horizontal direction, that is, perpendicular to the direction of gravity.

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