4 LEVELLING
4.1 Basic principles
Leveling is the name given to the process of measuring the difference in elevation between two or more
points. In engineering surveying, leveling has many applications and is used at all stages of construction
projects from initial site survey through the final setting out. Apart from the basic problem of determining
the relative heights of points, levelling has the following applications:
i. Contouring – for assessing topography
ii. Taking longitudinal sections to find ground profile for roads, pipelines (water, oil, etc), sewers, canals,
etc – i.e. along linear/ narrow works
iii. Taking cross-sections – at right angles to centrelines of roads, railways, etc
iv. Setting out levels – for pipelines, sewers, canals, buildings etc
A Level surface through A
Level surface through B
B Difference in
Elevation of A Elevation btn
A and B
Mean sea level Elevation of B
Vertical line
Vertical line
O
Definitions
Level surface: This is the level which is everywhere normal to the earth’s gravity, i.e. it is a curved surface
parallel to the mean surface of the earth.
Level line: It is a line lying on a level surface, hence a curved line.
,Horizontal plane: It is a plane which passes through a point at right angl;es to the direction of gravity at that
point. It is tangential to the level surface at that point.
Horizontal line: It is a line lying on the horizontal plane. A horizontal line through a point is tangential to
the level line which passes through the same point.
Datum surface: It is an arbitrary level surface to which heights of points may be referred. For many purposes
it is taken as the mean sea level, which is given a height value of zero (0.000 m). For example the mean sea
level value for Mombasa is the national datum for Kenya.
Mean Sea level- The average height of the sea’s surface for all stages of the tide over a very long period of
time. (Usually 19 years)
Bench mark (BM): This is a fixed point whose height has been established and with respect to which heights
of other points may be determined. It may be a block constructed for the purpose or could cut in stable
constructions such as houses or walls.
Reduced level: The elevation of a point w.r.t the adopted datum surface.
4.2 Methods of Levelling
Spirit Levelling; Geometric levelling using a spirit level which gives differences in height and depends on a
horizontal line of sight for this observation.
Trigonometric heighting: Determination of difference in height through the use of vertical angle as obtained
from, say a theodolite.
Barometric heighting: Determination of absolute height as based on the relationship between atmospheric
pressure and height.
Hydrostatic levelling: Determination of differences in height through the use of a hydrostatic level. A
hydrostatic level uses water in a tube to define the horizontal line of sight.
4.3 Levelling Instruments
There are three general types of engineer’s levels. These are: (i) Dumpy level (ii) Tilting level (iii) Automatic
or self-leveling level. Though the design of the three types differs, the operating principle is the same.
, a) Dumpy level
Basically a builder's level meant for not very high accuracy. The instrument is levelled only by the use of the
circular bubble and then used in that state throughout at a particular standpoint. Normally the instrument is
rotated about the vertical axis against friction as it does not possess a screw for locking motion about the
vertical axis
Vertical Axis
Horizontal Line
Line of sight
b) Tilting level
In this instrument the telescope is rigidly attached to the base of the level and can be tilted a small amount in
the vertical plane about a pivot placed below the telescope, hence the name tilting level. The amount of tilt
is controlled by the tilting screw, which is usually directly underneath the telescope eyepiece.
The level is designed such that for every observation, the instrument telescope is adjusted through the tilting
screw in order to set the line of sight horizontal for the particular reading; this assumes of course that the
instrument will have been levelled approximately by use of the circular bubble.
Vertical Axis
Horizontal Line
Line of sight
Tilting hinge
Tilting levels are adopted generally for the levels meant for more accurate work than the dumpy levels.
Tilting level technique is used for levels ranging from the engineer's level to the precise level.
4.1 Basic principles
Leveling is the name given to the process of measuring the difference in elevation between two or more
points. In engineering surveying, leveling has many applications and is used at all stages of construction
projects from initial site survey through the final setting out. Apart from the basic problem of determining
the relative heights of points, levelling has the following applications:
i. Contouring – for assessing topography
ii. Taking longitudinal sections to find ground profile for roads, pipelines (water, oil, etc), sewers, canals,
etc – i.e. along linear/ narrow works
iii. Taking cross-sections – at right angles to centrelines of roads, railways, etc
iv. Setting out levels – for pipelines, sewers, canals, buildings etc
A Level surface through A
Level surface through B
B Difference in
Elevation of A Elevation btn
A and B
Mean sea level Elevation of B
Vertical line
Vertical line
O
Definitions
Level surface: This is the level which is everywhere normal to the earth’s gravity, i.e. it is a curved surface
parallel to the mean surface of the earth.
Level line: It is a line lying on a level surface, hence a curved line.
,Horizontal plane: It is a plane which passes through a point at right angl;es to the direction of gravity at that
point. It is tangential to the level surface at that point.
Horizontal line: It is a line lying on the horizontal plane. A horizontal line through a point is tangential to
the level line which passes through the same point.
Datum surface: It is an arbitrary level surface to which heights of points may be referred. For many purposes
it is taken as the mean sea level, which is given a height value of zero (0.000 m). For example the mean sea
level value for Mombasa is the national datum for Kenya.
Mean Sea level- The average height of the sea’s surface for all stages of the tide over a very long period of
time. (Usually 19 years)
Bench mark (BM): This is a fixed point whose height has been established and with respect to which heights
of other points may be determined. It may be a block constructed for the purpose or could cut in stable
constructions such as houses or walls.
Reduced level: The elevation of a point w.r.t the adopted datum surface.
4.2 Methods of Levelling
Spirit Levelling; Geometric levelling using a spirit level which gives differences in height and depends on a
horizontal line of sight for this observation.
Trigonometric heighting: Determination of difference in height through the use of vertical angle as obtained
from, say a theodolite.
Barometric heighting: Determination of absolute height as based on the relationship between atmospheric
pressure and height.
Hydrostatic levelling: Determination of differences in height through the use of a hydrostatic level. A
hydrostatic level uses water in a tube to define the horizontal line of sight.
4.3 Levelling Instruments
There are three general types of engineer’s levels. These are: (i) Dumpy level (ii) Tilting level (iii) Automatic
or self-leveling level. Though the design of the three types differs, the operating principle is the same.
, a) Dumpy level
Basically a builder's level meant for not very high accuracy. The instrument is levelled only by the use of the
circular bubble and then used in that state throughout at a particular standpoint. Normally the instrument is
rotated about the vertical axis against friction as it does not possess a screw for locking motion about the
vertical axis
Vertical Axis
Horizontal Line
Line of sight
b) Tilting level
In this instrument the telescope is rigidly attached to the base of the level and can be tilted a small amount in
the vertical plane about a pivot placed below the telescope, hence the name tilting level. The amount of tilt
is controlled by the tilting screw, which is usually directly underneath the telescope eyepiece.
The level is designed such that for every observation, the instrument telescope is adjusted through the tilting
screw in order to set the line of sight horizontal for the particular reading; this assumes of course that the
instrument will have been levelled approximately by use of the circular bubble.
Vertical Axis
Horizontal Line
Line of sight
Tilting hinge
Tilting levels are adopted generally for the levels meant for more accurate work than the dumpy levels.
Tilting level technique is used for levels ranging from the engineer's level to the precise level.
