Civil Engineering Reference
In-Depth Information
enough to the centre of the sole plate. If the hole is not positioned correctly to allow this,
it should be extended to facilitate the correct positioning of the stump on the sole plate.
Concrete sole plates or pads
While not strictly the correct terminology, to save confusion I shall refer to the concrete
pad in the base of a stump hole as a concrete sole plate. Concrete sole plates when used in
conjunction with timber stumps should be poured into the bottom of the stump hole
and allowed to set before the timber stump is inserted into the hole. When pouring the
concrete into the hole, ensure that the top of the concrete is flat and as smooth as possible
so that the total surface of the bottom of the stump will be in contact with the concrete
sole plate.
Concrete and timber stumps
The most common mistake that people make when using concrete as the sole plate is the
belief that the concrete is to encase the stump to prevent it from moving. It is a standard
requirement for there to be 150 mm of concrete
under
the stump, however this should be
verified on your approved plans prior to construction. If the stump is positioned into the
hole and then the concrete poured around the stump, the stump will inevitably sink.
Whether it is a concrete or timber stump is of little consequence. When the concrete is
poured around the stump rather than under it the capacity of the sole plate is limited by
the adhesion of the concrete to the sides of the stump. When using concrete stumps this
is very limited. With timber stumps it is virtually nonexistent, as the timber stump will
react to the concrete and shrink away from it. An even worse scenario would be the use of
timber stumps with concrete sole plates where there is sufficient concrete under the
stump to prevent it from puncturing through the sole plate, and yet the concrete
surrounds the bottom of the stump (see Figure 3.2).
Water will travel through and around
the timber stump and create a pool of water
at the bottom of the stump. The concrete
will act as a reservoir for the water to sit in;
thereby keeping the bottom of the stump
wet for prolonged periods. Timber stumps
that are constantly in a wet environment
will rot. As if this is not enough of a
problem, when it comes time to remove the
rotted stump you will have to remove the
mass of concrete at the bottom of the hole
before fitting the new stump. If a timber
stump that has been fitted onto a flat sole
plate has to be replaced, it is simply a matter
of removing the stump, dig the soil out of
the original hole until the existing concrete
sole plate is uncovered. The new stump can
then be mounted on top of the existing
concrete sole plate.
Figure 3.2
Timber stumps encased in concrete
can lead to the degradation of the stump
