Chapter 5 Leveling

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Chapter (5)Leveling

• Introduction
• Leveling is the process by which differences in
  height between two or more points can be
  determined.
• Its purpose may be to provide heights or contours
  on a plan, to provide data for road
  cross-sections or volumes of earthworks, or to
  provide a level or inclined surface in the
  setting out of construction works.
• Instruments for Levelling
• The basic items of used instruments are the
  optical level and a graduated staff.
• Levels, Four types of levels are available
  optical, automatic, electronic, and laser.

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• Optical level
• An optical level is used to project a line of
  sight that is at a 90 degree angle to the
  direction of gravity.
• Both types, dumpy and tilting, use a precision
  leveling vial to .
• Orient to gravity. The dumpy type was used
  primarily in the United States, while the tilting
  type was of European origin and used in the
  remainder of the world. The dumpy level has the
  leveling vial fixed to the telescope, which is
  fixed at 90 degrees to a Rota table vertical
  spindle.
• Leveling screws, attached to the spindle, are
  used to center the leveling vial.

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Focusing Screw
line of collimation
Foot Screws
Components of Optical level
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• Automatic level
• Automatic levels use a pendulum device, in place
  of the precision vial, for relating to gravity.
  The pendulum mechanism is called a compensator.
• The pendulum has a prism or mirror, as part of
  the telescope, which is precisely positioned by
  gravity.
• The pendulum is attached to the telescope by
  using precision bearings or wires (metallic or
  nonmetallic).
• Leveling screws are used to roughly center a
  circular vial, and the optics on the pendulum
  then correct the line of sight through the
  telescope.
• Finally, Roughly leveled using a circular spirit
  level, then internal mechanisms take over to make
  sure the level remains level and maintains a
  horizontal sight.
• They are very popular, quick to set up and easy
  to use.

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Automatic Level with Compensator
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• Electronic level
• This type of instrument has a compensator similar
  to that on an automatic level, but the graduated
  leveling stall is not observed and read by the
  operator.
• The operator has only to point the instrument at
  a bar-code-type staff, which then can be read by
  the level itself. The electronic level eliminates
  human reading error and increases the speed at
  which leveling work can be performed.
• The only significant disadvantage is the high
  cost as compared to the optical automatic level.

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Electronic (Digital) level
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• Laser level
• Although this type of instrument is categorized
  as laser, these levels actually employ three
  different types of light sources tube laser,
  infrared diode, and laser diode.
• The instrument uses a rotating head to project
  the laser beam in a level 360 degree plane.
• The advantages are twofold no operator is
  required once the instrument is set up and
  different people in various locations can work by
  using a single light source.
• The disadvantages are that accuracy is less than
  that provided by other types of levels and that
  the cost is significantly higher.

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Laser Detector and staff
rotating head
Laser level (rotating head Laser Detector)
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Laser Detector
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• Leveling Rods
• Can be made of wood, metal, or fiberglass
  Graduated in meters.
• Rod levels are used to make sure that the rod is
  held vertical when making a reading.

Leveling Rods
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Rods Showing a Variety of Graduation Markings
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• Leveling - Field Procedures
• The process of leveling involves the transferring
  of elevations from a point of known elevation to
  points of unknown elevation by means of
  establishing a visual reference plane.
• This is done by setting up the level at any
  convenient point and leveling the instrument.
• The person then sights back to a level rod on a
  point of known elevation, usually referred to as
  a bench mark (BM).
• The rod reading, also known as a back sight
  (BS) or plus sight, is added to the known
  elevation of the bench mark to establish the
  height of instrument (HI).
• (This value is essentially the elevation of the
  center of the eyepiece of the level).

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• Now the person can sight forward to establish any
  number of points of unknown elevation.
• This is known as a fore sight (FS) or a minus
  sight.
• The rod reading for each fore sight is subtracted
  from the height of the instrument to establish
  the elevation for each new point.
• For points that cannot be seen from the initial
  instrument set-up, one foresight point can become
  a turning point (TP).
• The rod holder stays at this location while the
  instrument is moved forward to a new location.

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Leveling - Field Procedures
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Line of Sight This is the optical line produced
by the telescope of the instrument used for
sighting. In this particular case the line is
approximately horizontal. Reduced Level (R.L.)
The height of a point above the selected
datum. Mean Sea Level (M.S.L.) This is the
datum most frequently used. Datum for Egypt is
the Egyptian Height Datum (E.H.D.) Back sight
(B.S.) The first reading taken by an observer at
every instrument station.
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Foresight (F.S.) The last reading taken at an
instrument station . Intermediate sight (I.S.)
Any reading taken at an instrument station which
is NOT a permanent stable reference point. Bench
Mark (B.M.) A point of known Reduced Level
(R.L.). Usually a permanent stable is reference
point. Temporary Bench Mark (T.B.M.) Where only
relative heights are required or a bench mark is
required within area of work T.B.M. is
established .
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• Change Point (Turning point)
• The point at which the position of the instrument
  is changed, making it both a back sight and
  foresight.
• Summary of Levelling Procedure
• When the level has been set up we always start
  with a BS to a point whose RL is known such as a
  BM.
• The last reading at any instrument position is
  always a FS
• (i.e. always end with a FS).
• Either the instrument moves or the staff moves
  (never move both).
• We must always finish levelling at a point of
  known RL value such as an BM or a TBM (always
  close your levelling).

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Staff (Rod) Reading The following figures are
the samples of some readings in the rod.
Reading 1.932 m
Reading 1.133 m
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Example Set up and complete the differential
level notes for the information shown in the
accompanying illustration. All back sights are
shown to the left of the instrument diagrams and
foresights are shown to the right. All units are
feet.
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Solution
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Simple Calculation Check S FS - S BS
first RL - Last RL 30.67 - 22.09 100
91.42 8.58 8.58
O.k. Full Calculation Check S IS S FS S
(R.L. s except first)
S (each I.H. x number of applications 0.003
0.67366.34103.15x198.97x1 102.49x1
92.40x1 397.01 397.01
O.K Remember that 1- Simple Calculation Check S
FS - S BS 1st RL - Last RL 2-Full Calculation
Check S IS S FS S (R.L. s except first)
S (each I.H. x number of
applications)
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Example The following observations were taken in
leveling work 1.546, 1.562, 1.418, 1.390, 1.281,
(2.420), 1.321, 1.011, 2.007 m. The position of
the instrument was changed after the second and
seventh readings. Calculate the respective levels
of points at each staff if the first reading was
taken no B.M of RL 10.00 m and closed to B.M of
RL 9.09 m. It is important that to make
arithmetical check on your results. Note that
the staff readings enclosed by brackets were
taken with the staff reversed .
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Solution
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• Actual and Allowable Misclosure
• We have already seen that the
• Actual misclosure 9.085 - 9.09 -0.005m
• 5 mm
• Is this acceptable ?
• Allowable misclosure 5 vN mm
• Where N is the Number of Instrument Positions
• which is the same as Number of BS readings
• Therefore our Allowable misclosure 5 v3 mm
  8.66 say 9mm
• Therefore Actual lt Allowable
• Therefore our fieldwork is
• OK

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Simple Calculation Check S FS - S BS 1st
RL - Last RL 4.98 3.975 10.0
9.085 0.915 0.915
O.k. Full Calculation Check S IS S FS S
(RLs except first) S (each
I.H. x number of applications LHS 0.251
4.890 63.105 68.246 RHS 11.546x1
11.402x4 11.092x1 68.246 O.k.
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Example A level field book was found to be
tampered . The following readings were found to
be reliable . Complete the level field book with
respect to the given observations
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Check ?FS - ?BS 1st RL last RL 6.955 5.455
280.500 279.000 1.500 1.500