Civil Engineering Reference
In-Depth Information
Why you need to know the fall of the land
It is necessary to supply your draftsperson with details of the fall in the land, as this
must be indicated on your application for a building permit. It is also paramount in
determining the engineering requirements and final cost of the building. To look at it
and guess is not good enough. A difference of even a hundred millimetres can make a
significant difference. Underestimating this may mean that all the engineers' calculations
are incorrect and that the recommended construction system is inappropriate. Any
decent building equipment hire company will be able to hire you either a dumpy level or
a laser level. The dumpy level is simple to use and accurate to a few millimetres, more
than sufficient for the initial site inspection.
Ensure that you get instructions on how to set up and use the level that you hire prior
to leaving the hire company. Dumpy levels enable you to measure the variance in height
from one position to another. Mark the likely positions of the corners of the house on the
surface of the ground. Set up the dumpy level just outside the area of the house on higher
ground. One person will look through the dumpy level while another holds the staff on
the positions that you wish to take a reading from. A tripod on which the dumpy level is
to be mounted, and the staff will both be supplied with the dumpy level. Reading the
measurements off the staff in the various designated positions on the property will give
you comparative measurements. The smallest reading is to be the term of reference back
to which all other readings shall refer, and shall be deemed as zero or home base. Deduct
this smallest reading from the other readings to establish the height variance in the land
between the home base and each of the other positions. This is roughly the height the
stumps will protrude above ground level, or alternatively the depth of excavation
required.
If you do not feel confident to measure the fall of the land yourself, contact your
building consultant who may be able to assist you. If not, you will need to employ the
services of a land surveyor.
Excavation of a building site
What to allow for in the area of excavation
Prior to marking for excavation, establish the total flat area required for the house and
any surrounding landscape area. Include a drainage area for the removal of surface water
that may gather around the house, particularly between the house and the face of the
cutting, the deepest part of the excavation. If sullage lines and/or a septic tank are
required, discuss with your plumber their likely position and any necessary allowances
for them in the excavation.
Cut and fill excavation
On many occasions a building site is prepared by a method known as cut and fill. In this
method the soil removed is put on top of the lower area of the building envelope thereby
raising the lower land to the height of the excavation area, as shown in Figure 2.3.
