Attachment C - Geotechnical investigation

 

 

exend ourwards a minimum of 900 mum (more in highly reactive
soil) and should have a minimum fal! away from the building of
1:60. The finished poving should be no les than 100 mm below
brick vent bases.

Tcis prudent ro relocate drainage pipes away from this paving, If
possible, to. avold complications from future leakage If this is nor
practical, earthenware pipes should be rephiced by PVC and
backfilling should be of the same soil rype as the surrounding soil
and compacted to che same density.

Except in areas where freezing of water is an lasie, it is wise to
remove taps in the buikting area and relocate chem well away frou
the building — preferably noc uphill from ic (see BTF 19).

Tr may he desirable to install a grated drain at the curside edge of the

paving on the uphill side of the building. Ifsubsoll drainage ix
needed this can be installed under the surface drain,

Condensation

In buildings with a subfloor void such as where bearers and joists
support flooring, insufficient ventilation creates ideal conditions for
condensation, particularly where there Is little clearance between the
floor and the ground. Condensation adds to the moisture already
present in the subfloorand significantly slows the process of drying
our. Installation of an adequare subfloor ventilarion spscem, either
ratural or mechanical, is desirable.

Warning: Alchough this Building Technology File deals with
cracking in buildings, it should be mid thar subfloor moisture can
resulc in the development of other problems, notably:

* Wacer char is eansmiteed into masonry, metal or timber building
elements causes damage and/or decay two those elements.

* High subfloor humidiry and moisture content create an ideal
environment for various pests, including termites and spiders.

* Where high moisture levels are transmitted vo the flooring and
walls, an increase in the dust mine count can ensue within the
living areas. Dust mites, as well as dampness in general, can be a
health hazard tw inhabitants, particularly those who are
abnormally aasceprtible to respimarory ailmenn:

The garden

The ideal vegetation layour is co have lawn ot plants thar require only
Hight watering immedianely adjacene to the drainage ot paving edge,
then moce demanding planes, shrubs and tsees spread our in thar order.

Overwatering due to misuse of auvomaric watering symems iso
common canse of sarusarion and water migzarion under footings. IF ic
is necessaty to use these systems, it is important wm remove garden
beds to a completely safe distance from buildings.

Existing trees

Where a tee is canting a problem of soil drying or there is the
existence or threat of upheaval of footings, if the offending mow are
subsidiary and their removal will noe significantly damage the tree,
they should be severed and a concrete or metal harrier placed
vertically in the sail to prevent fucure root growth in the direction of
the building, If it is not poesible to remove the relevant mots withour
damage to the tree, an application to remove the tee should be made
wo the local authority, A prudent plan is w cransplanc likely offenders
before they become a problem.

Information on trees, plants and shrubs

regarding root pacterns, volume of water needed and safe distance
from buildings of most species. Boranic gardens ace also sources of
information. For information on plant wow and drains, see Building
Technology Pile 17.

Excavation

Excavation around footings must be properly engineered. Soil
supporting foorings can only be safely excavared aran angle thar
allows the soil under the footing to remain stable This angle Is called
the angle of repose (or Friction) and yaries between soil
types and condiriens Removal of sail within the angle of repose will
canse subsidence.

Where erosion has occurred that has washed away soil adjacent to
feoriugs, soll of the same classification should be imroduced and
ene ‘Where foorings have been
undermined, augmentation or other specialist work may be required.
Remediarion of footings and foundations is generally the realm of a
specialie consulrant.
Where isolated foorings rise and fall becanse of swell/shrink effect,
the homeowner may be tempered to alleviate Floor bounce by filling
the gup thar has appeared between the bearer and the pier with
blocking. The danger hese is thar when the next swell segment of che
cycle occurs, the extra blocking will push the floor up ino an.
accentuated dome and may also cause local shear failure in the soil. If
ir is necessary to use blocking, It should be by a pair of Fine wedges
and monitoring should be carried our fortnightly,
This BTF was prepared by John Lewer FAIR, MIAMA, Partner,
Construction Diagnosis.

‘Tho Infermetion in this and other Issues in the series was denved from various scuross and was Dateved to be correct when published.

 

The Information ts advisory. His provided In good falth and not claired to be an exhaustive treatment of the relevant subject,

 

Further professional advice needs to be obtained before tahing any action based on the information provided.

 

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