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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
INTRODUCTION
In this chapter the skills and knowledge associated with leveling operations will be
addressed. In particular the use of specialist leveling tools and equipment will be
explained as well as maintenance procedures for line of site instruments. Calculations
related to booking of level will also be explained. It should be read in conjunction with
“Basic Building and Construction Skills” 3rd edition, produced by South Western Sydney
Institute of TAFE and Pearson Education, Australia Pty Limited
Leveling terminology
Datum
This is any fixed reference point where the height or elevation of that point is known. A
position on a job site may be selected as a fixed reference point and is given an assumed
height, e.g. 100.0m, and all heights for the construction will be referred to that point for
the duration of the job. The nominated fixed point may be set on a permanent local
structure, tree, fence post, etc., and is then referred to as the job datum. It is shown on
plan in the form of a symbol, as shown below:
Figure 1 - Datum mark
R.L. 100.000
Site Benchmark
This is a fixed point of reference, which has a known height or elevation, and is formally
recorded for use by qualified Surveyors. There is usually a permanent mark either
chiseled into a concrete kerb, a metal plug set in a path or kerb, lines and arrows carved
into the face of a mature tree, marked with paint on the retaining walls at railway stations,
a stamp or metal plug on the plinth of a building or monument, etc
B.M.
Figure 2 -Typical Bench mark symbol
Reduced Level (RL)
This is a term given to the height or elevation of a point above or below a known point,
such as the given datum. Example: The assumed height of the Datum has an RL of
50.000m, and a point some distance away is set 1.000m above this datum then this point
would have an RL of 51.000m. If a point on the other side of this datum were 2.000m
below, it would have an RL of 48.000m, and so on. The assumed height of the datum is
always given as a large measurement so that points lower than the datum will not be
recorded as a negative measurement. See Figure 3
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Figure 3 - Working from a datum point
Laser levels
The Laser level consists of a laser
beam projected by a rotating
mirror horizontally, to a receiver.
The receiver may be hand held,
attached to a staff or placed
against an object and is moved up
or down until the laser beam is
received. The laser level is very
accurate over long distances and is
perhaps the most common form of
level reading devices used today.
Laser levels are set up either on a
tripod in the field or in indoor
Figure 4 - Rotating laser level
situations can be mounted on walls
with brackets.
Most laser levels use a class one laser, which emits a beam of light that can be harmful to
the eyes. Care must be taken to avoid directly looking into the beam.
Note: Laser levels can be easily operated by one person once set up
Telescopic levels
The telescope consists of:
 A pair of cross hairs, thin black lines set at 90° to one another visible through the
eyepiece, mounted in a ring or diaphragm near the rear of the telescope;
 Stadia lines, which are short cross hairs set above and below the main horizontal
cross hair. They are used to calculate the approximate distance of an object from
the instrument by subtracting the reading of the bottom hair from the reading of
the top hair, then multiplying the difference by 100.
 An eyepiece that magnifies the cross hairs. The cross hairs must be focused
according to the eyesight of the observer; and
 The object lens that forms an inverted image within the telescope.
Note: Two people are required to operate the telescopic level.
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Figure 5 - cross section of telescopic level
When a point is observed through the telescope, the line through the centre of the object
and the intersection of the cross hairs is referred to as the ‘line of sight’ or the ‘line of
collimation’.
The Quickset (or Builder’s) Level
This is a commonly used
instrument due to its simplicity
and ease of use. It consists of a
tripod with a ball and socket
mount to allow the instrument to
be moved in any direction to
obtain a level base. When the
central attaching screw is loosened
adjust the instrument until the
circular or bull’s-eye bubble is in
the centre, then tighten the screw.
Adjust the ‘tubular level bubble’
on the telescope to read level then
each time the telescope is moved
for a new sighting.
Figure 6 - The Quickset (or Builder's) level
The Tilting Level (or
Three screw)
Similar to the Quickset level
except for the method of
mounting on the tripod.
Figure 7 – Tilting level
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The Staff
The staff is a graduated measuring
rod for reading heights at the point or
station where the staff is held. It is
used together with a line of sight
instrument. Most staves are a
telescopic unit and extend to 5m.
The staff shown on the right has
typical “E” markings, graduated in
10mm increments. Some staffs are
marked with 5mm intervals.
Figure 2
Figure 8 - Staff markings
The line level:
The line level is used in conjunction
with string lines. A level bubble in a
casing can be suspended on a string
line. It is critical that the string line
be taut so an accurate reading can be
obtained.
Figure 3 - the line level
Note : the
line level is
not for
taking
critical
levels
Further advice and practice in using leveling equipment can be found at the following
Internet addresses:
http://www.levelling-simulation.com/ - A leveling simulation program. An evaluation
copy can be downloaded from this web address or contact
Manufacturing, Engineering, Construction & Transport Curriculum Centre, TAFE NSW,
PO Box 6941
Baulkham Hills Business Centre
NSW 2153
http://www.cage.curtin.edu.au/leap/virtu-o-modules/virtu-olevelling/1_LevellingModuleStart/1_LevellingModuleStart.html - Leveling training
courtesy of Curtin University.
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BEFORE USING LINE OF SIGHT INSTRUMENTS
Before using an optical level it is important to select a suitable stable location and
position the tripod to reduce the potential for accidental movement caused by bumping or
slipping feet on hard surfaces.
Cleared sites usually consist of soft earth into which the spiked feet of the tripod should
be pushed. On hard surface like paths and driveways you should look for cracks or joints
in the concrete into which feet may be placed. Placing sand bags on top of the feet will
prevent accidental bumping. If the level is to remain in position for an extended period
use barricades to protect the level from accidental movement. Always dismantle the leve
and return the level to its carrying case to before moving it to protect it from accidental
bumps and breakages.
Setting up an automatic level
Centring the Bull’s eye Bubbles
STEP 1. Rotate the base
until the bull’s-eye bubble is
between two of the base
adjusting screws. This will
leave the third screw directly
opposite the bubble on the far
side of the base.
STEP 2. Adjust the screws
up or down on either side of
Figure 4 - Centring the bubble
the bull’s-eye until the
moving bubble is close to the
middle of the bull’s-eye. This
may take two or three goes.
STEP 3. Using the third screw, opposite the bubble, adjust it up or down until the
moving bubble is at rest in the centre of the bull’s-eye, or at least within the centre ring.
Allow the moving bubble to settle, for approx. 10 seconds. For accuracy, turn the base
900, check and just the bubble if necessary. The adjustment screws should not be altered
or touched again, unless the instrument is moved or bumped.
Note: your trainer should demonstrate the methods used to set up each type of level.
Tubular Telescope Bubble
STEP 1. The tubular bubble is usually encased beside the telescope itself and may be
easily viewed through an attached hinged mirror, if provided. Turn the telescope towards
the object to be sighted and lock in position.
STEP 2. Adjust the telescope up or down using the tilting screw under the eyepiece.
Allow the bubble to settle, for approx. 10 seconds, and carry out fine adjustment until the
desired position between the marked lines is obtained. It is necessary to adjust the
telescope when it is rotated to a new position to maintain the same line of sight.
Note: A similar method is used to adjust split bubble, which may be found on some
instruments.
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The Dumpy or Automatic level:
The Dumpy level takes a little more time to set up, as there is no ‘tilting screw’ for the
telescope. However, once set up there is no need to level the telescope each time it is
rotated, unless it is moved or bumped. Use the same method as described in setting the
bull’s eye bubble.
Adjusting the cross hairs and using Stadia lines
Before any readings can be taken accurately
the cross hairs as seen through the telescope,
need to be adjusted to their crispest focus.
Turning the eyepiece in the telescope until
the cross hairs and Stadia lines are in clear
focus does this.
With the cross hairs in clear focus the
object, usually the staff needs to be bought
into focus now by turning the lens focus
adjustment at the front of the telescope
Figure 5 - view through telescopic level
showing cross hairs and Stadia lines
Testing and adjusting the level for collimation error
Taking level readings it is important to
check that level is in correct adjustment. To
do this you can use the two peg method is
commonly used. The two-peg test will
determine if there is a difference between
the actual line of sight (line of collimation)
and the true horizontal line. If a difference is
found, (e) the user to can adjust the line of
sight so it coincides with the horizontal
plane. The objective is to eliminate the error
in readings that may occur known as the
collimation error.
The steps used to perform the task are
outlined below.
Figure 6 - Difference between the horizontal plane
the line
of sight
1. Select a suitable test range. The area should be flat andand
about
75 to
100 metres
long.
2. Hammer 300 x 25 x 25mm wooden pegs firmly into the ground at each end of the
range. The pegs must be into firm ground to ensure they do not sink or move
when the staff is set on them. One peg will be for the backsight (BS peg) and the
other for the foresight (FS peg) as in figure 11
3. Set the level up about midway an in a straight line between the BS and FS pegs.
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4. Take the reading to the staff on the BS peg and record the reading. Then take the
reading to the staff on the FS peg and book the reading.
Back sight
Intermediate Foresight
reading
Rise
Fall
1.425
1.360
5. Move the level closer to the BS peg
(e.g. 3 metres) and in line with FS
peg.
6. Take the readings to the BS peg and
book the reading. Take the readings
FS peg and book the reading.
Back sight
Figure 7 - Move the level closer to the
backsight position
Intermediate Foresight
reading
Rise
Fall
1.425
1.360
0.065
1.415
0.038
1.453
Collimation error =
0. 027
7. Calculate the collimation error: which = the difference between the two rise
readings. If the level is reading accurately the rise calculations should be equal.
Making the collimation error come to 0.
Back sight
Intermediate Foresight
reading
Rise
1.425
1.360
0.065
1.415
0.038
1.453
Collimation error =
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0. 027
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8. Adjust the cross hairs to the correct staff reading. This is usually done with an
Allen key in a set just below the eyepiece. Finally cross check the readings. This
may need to be done a couple of times
Using the Staff
The staff is essentially a graduated measuring rod for reading heights at the point or
station where the staff is held. When taking several readings, a greater reading would
indicate a fall whereas a lesser reading would indicate a rise. Most staves are made as a
telescopic unit, which may be extended to 5m in height. Single staves may be made from
seasoned timber but the majority of telescopic types are made from fibreglass or
Aluminium with coloured markings to allow ease of reading.
It is important to hold the staff as plumb as possible, in both directions, when readings
are taken so that accuracy is maintained. Some staves may even be fitted with a bubble
for just this purpose.
Shown below are two common staff faces, one with a graduated face and the other with
an ‘E’ pattern face.
Note: Figure
27 shows
reading
positions as
viewed through
an older type of
leveling
instrument,
which shows
the image in the
inverted
position.
Figure 8 - Reading common staffs
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Figure 9 - inverted readings on older types of levels
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SITES AND RECORDING INFORMATION
Line of Collimation
This is the line of sight taken through the eyepiece,
centre of the cross hairs of the telescope and the
centre of the object being viewed. It is important to
note that the instrument should be set at a height to
suit the viewer so it is not necessary to bend or
stretch to take a reading as this may lead to ‘an error
of parallax’ occurring, which means looking
through the eyepiece at an angle above or below the
cross hairs resulting in an incorrect reading. This
imaginary line remains straight and level in all
directions as the telescope is rotated to provide a
constant common line from which to measure so an
accurate picture of the surface being surveyed can
be created. Once the reduced level of the datum or
benchmark is known, all other sights may also be
Figure 10 - Parallax error
given a reduced level, which is either above or
below the datum or benchmark.
This information can be used to create a contour map of the site or area being surveyed so
builders and designers can use it to determine floor levels, DPC levels, falls, cut and fill
requirements, structural design requirements, etc.
It is important the test the accuracy of levels each time before use as small bumps and
knocks can affect the reading taken.
Figure 11 - Method of reading ad recording rise and fall
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BOOKING OF LEVELS
To record a Traverse, a straight-line survey, or a Closed Traverse, a survey around a site,
the readings need to be logged onto a table or ‘Level Book’ so the rises, falls, reduced
levels and distances may be calculated. This information will be useful when setting out
the site to identify areas to be excavated or filled, heights of floors, drainage, etc.
Level Book Terminology
Backsight
This is the first sight taken and recorded after the leveling instrument is set up. It is
usually taken from the Datum or Benchmark or Job Datum to establish a starting point
and show the height of the instrument in relation to that known point.
Intermediate Sight
These are all the sights taken at nominated positions; known as stations, to enable a
running calculation of rises and falls, which are used to determine the Reduced levels.
Foresight
This is the last sight taken before the instrument is moved to another location or when a
traverse is complete.
Change Station
This is a point at which two readings are taken because the instrument has to be moved
due to not being able to see the next intermediate sight from that set up position. The
first sight taken at a change point will be recorded as a Foresight, because it is the last
sight taken before the instrument is moved, and the second sight taken will be recorded as
a Backsight, because it is the first sight taken once the instrument is set up again. This
procedure allows the traverse to continue which in turn allows the Reduced levels to
continue in sequence, giving the impression that there was no obstacle or disruption in
the leveling process.
Rise
This is a measurement calculated by subtracting the last two sights from one another, i.e.
an intermediate sight from the backsight or an intermediate sight from an intermediate
sight or a foresight from an intermediate sight, etc. If the height or elevation of the
second sight is less than the first sight, then the difference in measurement will be
recorded as a ‘rise’.
Fall
Same method of calculation as for the rise, but if the height or elevation of the second
sight is greater than the first sight, then the difference will be recorded as a ‘fall’.
Reduced Level
These are the finished calculated heights or elevations in relation to the original reduced
level, which was recorded as the identified Datum or Bench Mark. To calculate these
levels it is necessary to add the rises and subtract the falls.
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Remarks
These are comments made relating to the start and finish of the traverse or to indicate a
change in station, intermediate sight, special landmark, etc.
Example of a Level Book page;
Backsight Intermediate Foresight Rise Fall
Sight
Reduced
Levels
Distance
Remarks
METHOD OF BOOKING LEVELS
The following example outlines the sequence required to book levels, calculate the rise
and fall, calculate the reduced levels and identify where the levels were taken.
Example 1:
A traverse or straight-line survey is to be taken, at 5.0m intervals through the centre of a
large residential block, which is to be subdivided. There are two existing buildings on
the block which will obscure the view of some points from the first set up position,
therefore a change station is required.
Figure 12 - Plan and section of block to be sub-divided
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Step 1. The first set up position of the level should be where the greatest number of
stations and the datum or benchmark can be seen. This will avoid unnecessary moving of
the instrument. This position is identified as ‘L1’. The reading taken here back to the
identified benchmark on the kerb and gutter, at the north/east corner of the block, is
1.575m. This is the relative height of the instrument above the benchmark and as it is the
first sight taken it will booked as a Backsight. . The actual Reduced Level of the Bench
Mark is also recorded.
Backsight Intermediate Fore sight
Rise
Fall
Sight
Reduced Distance
Remarks
Level
1.575
47.195
0
B.M. & L1 (start)
Step 2. Book all the intermediate sights before the instrument has to be moved. Include
the progressive distance, starting at 2.0m from the Bench Mark.
Backsight Intermediate Foresight
Sight
Rise
Fall
Reduced
Levels
Distance
Remarks
47.195
0
B.M. & L1 (start)
1.250
2
Station 1
0.850
7
Station 2
1.330
12
Station 3
1.580
17
Station 4
1.575
Step 3. The next station, i.e. S5, will be when the instrument has to be moved as the
station after it, i.e. S6, cannot be seen from position L1. This will be the last sight taken
from L1; therefore the sight will be recorded as a Foresight. Note: When relocating the
instrument it must be in a position where S5 can be seen so a backsight may be taken
from the new position.
Backsight Intermediate Foresight
Sight
Rise
Fall
Reduced
Levels
Distance
Remarks
47.195
0
B.M. & L1 (start)
1.250
2
Station 1
0.850
7
Station 2
1.330
12
Station 3
1.580
17
Station 4
22
Change Station 5
1.575
1.450
Step 4. The instrument has been relocated to position L2, therefore the first sight taken
after setting up will be back to S5 and will be booked as a Backsight.
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Step 5. Book all other intermediate stations through to S9.
Backsight Intermediate Foresight
Sight
Rise
Fall
Reduced
Levels
Distance
Remarks
47.195
0
B.M. & L1 (start)
1.250
2
Station 1
0.850
7
Station 2
1.330
12
Station 3
1.580
17
Station 4
22
Change Station
(No
change)
L2 & Change St.
5
1.980
27
Station 6
1.760
32
Station 7
1.710
37
Station 8
1.840
42
Station 9
1.575
1.450
2.550
Step 6. The final sight, at S10, is also the last sight before the instrument is moved,
therefore it will be booked as a Foresight. It should also be noted in the remarks column
that this is the end of the traverse.
Backsight Intermediate Foresight
Sight
Rise
Fall
Reduced
Levels
Distance
Remarks
47.195
0
B.M. & L1 (start)
1.250
2
Station 1
0.850
7
Station 2
1.330
12
Station 3
1.580
17
Station 4
22
Change Station 5
(No
change)
L2 & Change St. 5
1.980
27
Station 6
1.760
32
Station 7
1.710
37
Station 8
1.840
42
Station 9
47
Station 10 (end)
1.575
1.450
2.550
1.920
Step 7. The next step is to determine the rises and falls and book them in the appropriate
column. When a sight has a lesser elevation than the previous sight, it will be classified
as a ‘Rise’. When a sight has a greater elevation than the previous sight, it will be
classified as a ‘fall’.
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Backsight Intermediate Fore sight
Rise
Fall
Sight
Reduced
Distance
Remarks
0.000
B.M. & L1 (START)
Level
1.575
47.195
1.250
0.325
2.000
Station 1
0.850
0.400
7.000
Station 2
0.480
12.000
Station 3
0.250
17.000
Station 4
22.000
Change station 5
1.330
1.580
1.450
0.130
2.550
(No change) L2 & Change station 5
1.980
0.570
27.000
Station 6
1.760
0.220
32.000
Station 7
1.710
0.050
37.000
Station 8
0.130
42.000
Station 9
0.080
47.000
Station 10 (end)
1.840
1.920
Step 8. The Reduced Levels are now calculated by ‘adding the rises’ and ‘subtracting
the falls’. Each measurement is either added or subtracted from the previous Reduced
Level total.
Backsight Intermediate Fore sight
Rise
Fall
Sight
Reduced
Distance
Remarks
47.195
0.000
B.M. & L1 (START)
Level
1.575
1.250
0.325
47.520
2.000
Station 1
0.850
0.400
47.920
7.000
Station 2
0.480
-47.440
12.000
Station 3
0.250
-47.190
17.000
Station 4
47.320
22.000
Change station 5
1.330
1.580
1.450
0.130
2.550
47.320
(No change) L2 & Change station 5
1.980
0.570
47.890
27.000
Station 6
1.760
0.220
48.110
32.000
Station 7
1.710
0.050
1.840
1.920
48.160
37.000
Station 8
0.130
-48.030
42.000
Station 9
0.080
-47.950
47.000
Station 10 (end)
Step 9. To ensure the sights have been placed in the correct columns and the rises and
falls are in the correct columns, a check is made in three areas:
1. Add the backsights together, then add the foresights together and find the difference
between them:
2. Add the rises together, then add the falls together and find the difference between
them.
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3. Subtract the first reduced level from the last reduced level and find the difference
between them. If all three differences are the same, then the book is said to be balanced.
Backsight Intermediate
Fore sight
Rise
Fall
Reduced
Sight
0
B.M. & L1 (START)
0.325
47.52
2
Station 1
0.850
0.400
47.92
7
Station 2
12
Station 3
1.330
0.480
-47.44
1.580
0.250
-47.19
17
Station 4
47.32
22
Change station 5
0.130
47.32
2.550
(No change) L2 & Change station 5
1.980
0.570
47.89
27
Station 6
1.760
0.220
48.11
32
Station 7
1.710
0.050
48.16
37
Station 8
0.130
-48.03
42
Station 9
0.080
-47.950
47
Station 10 (end)
1.840
1.920
4.125
Balanced
47.195
1.250
1.450
And
Remarks
Level
1.575
Check:
Distance
3.370
Backsights/Foresights
Rise/Falls
Reduced Levels
1.695
0.940
:
4.125
-
3.370
=
0.755
:
1.695
-
0.940
=
0.755
:
47.950
-
47.195
=
0.755
Performing these check and balance calculations confirms accuracy.
A site contour plan can be developed from the booked information.
Figure 13 - A typical contour
site plan
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Reduced Level
The known point, referred to as the datum or benchmark, is also given a reduced level
and all the contours are shown on plan either above or below this point.
Note: The datum or benchmark is never given as zero as there may be falls on the site,
which would result in a negative measurement being shown.
As contour lines have reduced levels it is easy to determine the difference in height from
one corner of the building to the other. In the plan above, it is also possible to calculate
the depth of the excavation in each corner of the garage or the height from floor level to
ground level at a number of points in the building.
The site is usually set out to a grid with a grid spacing to suit the slope of the site, i.e.
smaller grids for steep or undulating sites, to record the most information for establishing
changes in elevation, and larger grids for relatively level sites, as less detail is required.
The average gently sloping building block may be set out to 5.0m grid spacings, which is
determined prior to booking levels, and the calculated reduced levels may then be plotted
to the intersection points on a grid plan.
Contour Intervals
This is the vertical height or elevation between adjacent contour lines. On steeply sloping
sites the contour interval may be greater, e.g. 1.0m intervals, than that required for gently
sloping sites, e.g. 50, 100 or 200mm intervals, depending on the accuracy required.
Figure 14 - Sample part grid plan
Step 1. Start from the highest point on the grid and select two adjacent grid points, e.g.
C1 and B1, on the grid plan. Subtract one reduced level from the other, i.e. 110.800 110.600 = 200mm;
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Step 2. Divide the difference between the reduced levels by the nominated contour
interval, e.g. 100mm, which would equal 200 ¸ 100 = 2 divisions:
Step 3. Mark the 2 equal spacings on the grid plan line between C and B:
Step 4. Repeat the process between grid points C1 and C2:
Step 5. Identify the position of the contours with the same contour interval and join them
with a line, which should be curved in the direction of highest to lowest position. The
degree of curve may be determined by selecting the diagonally opposite grid points
which have the highest and lowest reduced levels. Subtract one from the other and divide
them into the same contour interval spacings, then join all the like points.
Figure 15 - Method for dividing contour grids
Note: Where the contour lines are shown as a circle on plan it would indicate the peak of
a hill or the depression of a hole.
Step 6. Repeat the process between all other adjacent grid intersections until a
completed contour map is revealed:
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
FURTHER READING
Acceptable Standards of Construction Committee, 1998, Acceptable Standards of
Domestic Construction, Acceptable Standards of Construction Committee Inc, Sydney
Barrington, J., D. Mylius & S. Arden, 1989, Book 1 Practical Australian Carpentry,
Framing and Construction, McGraw Hill, Sydney
Brown, B. and H. Slatyer, 1985, First published 1958, Second edition 1966, Third edition
1975, Fourth edition 1981, Fifth edition 1985, The Australian Carpenter and Joiner Volume 1, Standard Publishing Co Pty Ltd, Victoria.
National Committee on Rationalised Building, 1994, Fourth edition, Glossary of Building
Terms, Standards Australia, Sydney.
Simpson, Charles. and Barry Hodgson, 1995, Building a House - Framing Practices,
Macmillan Education Australia, South Melbourne.
Teachers of Building, 2004, Basic Building and Construction Skills, 3rd Edition, SWSI
TAFE NSW and Pearson Education, Australia Pty Ltd, South Melbourne.
Videos
MECAT Curriculum Centre, Setting Out Techniques, (CTV07), Basic Leveling,
(CTV05), Setting Out a Building Site (CTV10) available from Resource Distribution,
Yagoona.
Web sites
http://www.levelling-simulation.com/ - A leveling simulation program.
http://www.arpansa.gov.au/is_laser.htm - Safe use of laser levels
http://www.cage.curtin.edu.au/leap/virtu-o-modules/virtu-olevelling/1_LevellingModuleStart/1_LevellingModuleStart.html - Virtual leveling
simulation and training courtesy of Curtin University.
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
ACTIVITIES AND EXERCISES
Activity sheet1.
1. Is it OK to put the water level away full of water with the plugs sealing the ends
of the hose?
It is better to empty the water level after use as this prevents the possibility of water
leaking from the ends, and the prevents water stagnating in the tube, which could
cause a health hazard.
2. During a site clean up after leveling the set out profiles for a construction site, can
I remove the site survey pegs?
No, leave the site survey pegs in position at all times. You will need them to
refer back to, for different construction operations like drainage and pier heights or slab.
levels or especially if your set out pegs are knocked out of place
3. Explain what a Datum mark is and what is it used for?
This is any fixed reference point where the height or elevation of that point is known.
4. What is a site bench mark and where can they be located, who uses them and
what is it used for?
This is a fixed point of reference, which has a known height or elevation, and can
usually be found on a metal plug set in a path or kerb.
5. Explain the term reduced level.
This is a term given to the height or elevation of a point above or below a known point,
such as the given datum.
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
6. Name the 3 main components required in a telescope to help take readings, apart
from the tripod and leveling bubbles, and briefly describe how do they help to
establish levels:
1.
cross hairs - for lining up the object
2.
Stadia lines - for checking distance
3.
Eye piece – to focus the cross hairs
7. What is the alternative to a telescopic level?
A laser level
8. A measuring staff is used in conjunction with a telescopic level and a laser level;
describe how the markings are set out on the face of the staff.
A typical staff has “E” markings, graduated in 10mm increments. Some staffs are marked
of using 5mm intervals.
9. When setting up a tripod what can you do to stabilise the tripod base?
On hard surface like paths and driveways you should look for cracks or joints in the
concrete into which feet may be placed. Placing sand bags on top of the feet will prevent
accidental bumping.
10. What is the name of the common test used to adjust for collimation error in a
telescopic level when it has been set up?
The two peg test is used to determine if there is a difference between the actual line of
sight (line of collimation) and the true horizontal line.
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
Activity sheet 2
1. Describe the purpose of a ‘Level Book’
Readings from the level and staff need to be logged onto a table or ‘Level Book’ so the
rises, falls, reduced levels and distances may be calculated. This information will be
useful when setting out the site to identify areas to be excavated or filled, heights of
floors, drainage, etc.
2. The following terms are column heading in a “level Book”.
Define the term and describe the function of each column.
a.
Backsight
b.
Intermediate site
c.
Foresight
d.
Change station
e.
Rise
f.
Fall
g.
Reduced level
h.
Remarks
Backsight:
This is the first sight taken and recorded after the leveling instrument is set up. It is and
usually taken from the Datum or Benchmark or Job Datum to establish a starting point
show the height of the instrument in relation to that known point.
Intermediate sight:
These are all the sights taken at nominated positions, known as stations, to enable a
running calculation of rises and falls, which are used to determine the Reduced levels.
Foresight:
This is the last sight taken before the instrument is moved to another location or when a
traverse is complete.
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
Change station:
This is a point at which two readings are taken because the instrument has to be moved
due to not being able to see the next intermediate sight from that set up position. This
procedure allows the traverse to continue which in turn allows the Reduced levels to
continue in sequence, giving the impression that there was no obstacle or disruption in
the leveling process.
Rise:
The rise is calculated by subtracting the last two sights from one another,
If the height or elevation of the second sight is “less than” the first sight, then the
difference in measurement will be recorded as a ‘rise’.
Fall:
The same method of calculation is used as for the rise, but if the height or elevation of
the second sight is “greater” than the first sight, then the difference will be recorded as a
‘fall’.
Reduced level
These are the finished calculated heights or elevations in relation to the original reduced
level, which was recorded as the identified Datum or Bench Mark. To calculate these
levels it is necessary to add the rises and subtract the falls.
Remarks column:
These are comments made relating to the start and finish of the traverse or to indicate
a change in station, intermediate sight, special landmark, etc.
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BCGCA3023B - CARRY OUT LEVELLING OPERATIONS
3. When balancing a “Level Book” to ensure the sights have been placed in the
correct columns and the rises and falls are in the correct columns, a check is made
in three areas. What are the three checks?
a.
Add the backsights together, then add the foresights together and find the
difference between them
b.
Add the rises together, then add the falls together and find the difference between
them.
c.
Subtract the first reduced level from the last reduced level and find the difference
between them.
3. What are Contour Lines?
Where the are shown as a circle on plan it would
Contour lines indicate the peak of a hill or the depression of a hole and are usually shown
as curved lines on a site plan.
4. What are Contour Intervals?
This is the vertical height or elevation between adjacent contour lines. They will be at
1metre intervals for steeply sloping sites or 5 metre intervals for gently sloping sites,
depending on the accuracy required.
5. Where on a building site would you normally start taking reading to prepare a
contour plan?
From the highest corner of the site
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6. Activity sheet 3.
You trainer can direct you to a suitable simulated “construction site”. He will provide you
with the necessary information to allow you take readings and book levels. The sheet
below can be used to record the data and perform the check calculations.
Backsight Intermediate Foresight Rise Fall
Sight
Reduced
Levels
Distance
Insert totals required for each column as
indicated
Check:
And
Balanced
Backsights/Foresights
:
-
=
Rise/Falls
:
-
=
Reduced Levels
:
-
=
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Remarks