BUILDING SITE SURVEY AND SET
OUT
Carrying out a level traverse
To determine the difference in level between points on the surface of
the ground a 'series' of levels will need to be carried out; this is called
a level traverse or level run.
There are two method of levelling:
 Rise & Fall method and
 Height of collimation (height of instrument) methods
Click the link to see the animated rise&fall methods then click next for the height of collimation method. Please note when the shifting of the staff or level can be done using the rise&fall method
Leveling or Field Procedures
The leveling or field procedure that should be followed is shown in Figure 1
below..
Figure 1
Procedure:
 Set up the leveling instrument at Level position 1.
 Hold the staff on the Datum (RL+50 m) and take a reading. This will
be a backsight, because it is the first staff reading after the leveling
instrument has been set up.
 Move the staff to A and take a reading. This will be an intermediate
sight.
 Move the staff to B and take a reading. This also will be an
intermediate sight.
 Move the staff to C and take a reading. This will be another
intermediate sight.
 Move the staff to D and take a reading. This will be a foresight;
because after this reading the level will be moved. (A changeplate should
be placed on the ground to maintain the same level.)
 The distance between the stations should be measured and recorded
in the field book (see Table 1)
 Set up the level at Level position 2 and leave the staff at D on
the changeplate. Turn the staff so that it faces the level and take
a reading. This will be a backsight.
 Move the staff to E and take a reading. This will be an intermediate
sight.
 Move the staff to F and take a reading. This will be a foresight;
because after taking this reading the level will be moved.
 Now move the level to Leveling position 3 and leave the staff at F
on the changeplate.
Now repeat the steps describe 8 to 10 until you finished at point J.
Field procedures for leveling
All staff readings should be recorded in the field book. To eliminate
errors resulting from any line of sight (or collimation) backsights and
foresights should be equal in distance. Length of sight should be kept
less than 100 metres. Always commence and finish a level run on a known
datum or benchmark and close the level traverse; this enables the level
run to be checked.
Booking levels
There are two main methods of booking levels:
 rise and fall method
 height of collimation method
Table 1 Rise & Fall Method
Back
sight

Inter
mediate

Fore
sight

Rise

Fall

Reduced
level

Distance

Remarks

2.554





50.00

0

Datum RL+50 m


1.783


0.771


50.771

14.990

A


0.926


0.857


51.628

29.105

B


1.963



1.037

50591

48.490

C

1.305


3.587


1.624

48.967

63.540

D / change point 1


1.432



0.127

48.840

87.665

E

3.250


0.573

0.859


49.699

102.050

F / change point 2


1.925


1.325


51.024

113.285

G

3.015


0.496

1.429


52.453

128.345

H / change point 3



0.780

2.235


54.688

150.460

J

10.124


5.436

7.476

2.788

54.688


Sum of Bsight & Fsight,
Sum of Rise & Fall

5.436



2.788


50.000


Take smaller from greater

4.688



4.688


4.688


Difference should be equal

The millimeter reading may be taken by estimation to
an accuracy of 0.005 metres or even less.
 Backsight, intermediate sight and forsight readings are entered in
the appropriate columns on different lines. However, as shown in the
table above backsights and foresights are place on the same line if
you change the level instrument.
 The first reduced level is the height of the datum, benchmark or R.L.
 If an intermediate sight or foresight is smaller than the immediately
preceding staff reading then the difference between the two readings
is place in the rise column.
 If an intermediate sight or foresight is larger than the immediately
preceding staff reading then the difference between the two readings
is place in the fall column.
 A rise is added to the preceding reduced level (RL) and a fall is
subtracted from the preceding RL
Arithmetic checks
While all arithmetic calculations can be checked there is no assurance that
errors in the field procedure will be picked up. The arithmetic check proves only that the rise and fall is correctly recorded in the appropriate rise & fall columns. To check the field procedure
for errors the level traverse must be closed. It is prudent to let another student
check your reading to avoid a repetition of the level run.
If the arithmetic calculation are correct, the the difference between the sum
of the backsights and the sum of the foresights will equal:

the difference between the sum of the rises and the sum of the falls,
and
 the difference between the first and the final R.L. or vice versa.
(there are no arithmetic checks made on the intermediate sight calculations.
Make sure you read them carefully)
Back
sight

Inter
mediate

Fore
sight

Height of
collimation

Reduced
level

Distance

Remarks

2.554



52.554

50.00

0

Datum RL+50 m


1.783



50.771

14.990

A


0.926



51.628

29.105

B


1.963



50591

48.490

C

1.305


3.587

50.272

48.967

63.540

D / change point 1


1.432



48.840

87.665

E

3.250


0.573

52.949

49.699

102.050

F / change point 2


1.925



51.024

113.285

G

3.015


0.496

55.468

52.453

128.345

H / change point 3



0.780


54.688

150.460

J

10.124


5.436


54.688


Sum of Bsight & Fsight,
Difference between RL's

5.436




50.000


Take smaller from greater

4.688




4.688


Difference should be equal

 Booking is the same as the rise and fall method for back, intermediate
and foresights. There are no rise or fall columns, but instead a height
of collimation column.
 The first backsight reading (staff on datum, benchmark or RL) is added
to the first RL giving the height of collimation.
 The next staff reading is entered in the appropriate column but on
a new line. The RL for the station is found by subtracting the staff
reading from the height of collimation
 The height of collimation changes only when the level is moved to
a new position. The new height of collimation is found by adding the
backsight to the RL at the change point.
 Please note there is no check on the accuracy of intermediate RL's
and errors could go undetected.
The rise and fall method may take a bit longer to complete, but a check
on entries in all columns is carried out. The RL's are easier to calculate
with the height of collimation method, but errors of intermediate RL's
can go undetected. For this reason students should use the rise and fall
method for all leveling exercises.
Closed and open traverse
Always commence and finish a level run on a datum, benchmark
or known RL. This is what is known as a closed level traverse,
and will enable you to check the level run.
Closed level traverse
Series of level runs from a known Datum or RL to a known Datum or
RL.
Misclosure in millimeter
24 x √km
Closed loop level traverse
Series of level runs from a known Datum or RL back to the known
Datum or RL.
Misclosure in millimeter
24 x √km
Open level traverse
Series of level runs from a known Datum or RL. This must be avoided because
there are no checks on misreading
Areas
Area calculations refer usually to rectangular and triangular shapes.
If you need the trigonometric function for calculations click here.
There
are different ways to calculate the area of the opposite figure. Try to
minimise the amount of calculation. The figure could be divided in three
distinct areas
a=10.31x5.63+
b=6.25x5.76+
c=10.39x4.79
or the whole rectangle minus the hole (d)
A =16.67x10.316.25x4.55.
As you can see the 2nd method is easier. Look at the shape and try to
shorten the calculations.
If you know only the sides of a triangle then use the formula given in
the figure below.
An area can usually be divided it in triangles (rectangles, parallelograms,
trapeziums etc).
Parallelograms has opposite
sides parallel and equal. Diagonals bisect the figure and opposite angles
are equal..
The trapezium has one pair of opposite sides parallel.
(A regular trapezium is symmetrical about the perpendicular
bisector of the parallel sides.)
An arc is a part of the circumference of a circle; a part proportional to the
central angle.
If 360° corresponds to the full circumference. i.e. 2
r then for a central angle of
(see opposite figure) the corresponding arc length will be b = /180
x
r .
Volumes
Volume calculations for rectangular prism and pyramid are shown below:
A truncated pyramid is a pyramid
which top has been cut off.
If the A_{1}+A_{2} is almost equal in size then the following
formula can be used instead:
V = h × (A_{1} + A_{2}) / 2
A prismoid is as a solid whose end faces lie in parallel planes and consist of any two polygons, not necessarily of the same number of sides as shown opposite, the longitudinal faces may take the form of triangles, parallelograms, or trapeziums.
