Civil Engineering Reference
In-Depth Information
second tape measure you have a position that is square to the original string line. Insert a
third peg at this position and fit a nail at the exact junction point. Extend a string line
from the nail in the corner peg directly across the nail in the third peg to determine the
line of the new wall. Extend a tape measure in the same line to determine the position of
the new corner peg lengthwise (see Figure 2.6).
Figure 2.6
Marking the position of the wall at a right angle to the first wall
To plot the position of the final peg, simply measure from the nail in the third peg
the correct length of the wall back to the position of the final corner peg. Now measure
the length of the remaining wall. Where the two measurements intersect will in theory be
the final position of the last peg. As a double check, measure the diagonal distance across
the building site between the diagonally opposite pegs, and then for the opposing
diagonally opposite pegs. If the measurement is the same then your markers are square. If
not you may need to adjust the corner peg positions slightly to gain a true square
position. The external corners of the building are now established, however this
information will be lost with the first stroke of the backhoe or as soon as the holes are
dug for the corner postholes. Consequently, this information will be transferred to
hurdles as shown previously.
Transferring the details to the hurdles
You will need to transfer the house position details to the hurdles for future reference. Tie
a string line to the nail on one of the corner markers and then pull the string line directly
across the nail in the corner peg representing the other extremity of that wall - just as you
did when marking for the original excavation. Extend the string about 3 metres past the
marker, as this will be the location of the hurdle. Ideally the hurdles should be placed
approximately 3 metres beyond the actual building area to reduce the possibility of the
backhoe or posthole digger moving them. Hammer a peg into the ground at this distance
from the building site, approximately 300 mm to one side of the string line, and a second
peg 300 mm to the other side. Fit the cross rail that will need to be about 800 mm long to
these pegs approximately 300 mm above the ground. Mark a line on the hurdle directly
above the string line. You could use a level or a plumb bob to transfer this line vertically
to the hurdle. Repeat this process first for the other end of the same wall and then for
each of the walls. Once you have all the hurdles in position with marks in each of them,
hammer a 50 mm nail into the hurdle at the mark. Stretch a string line between all these
nails thereby representing the outside walls of the house.
