Attachment B - Geotechnical Analysis

 

extend ourwards a minimum of 900 mm (more in highly reactive
soil) and should have a minimum fall away from the building of
1:60. The finished paving should be no less than 100 mm below
brick vent bases.

It is prudent to relocate drainage pipes away from this paving, if

possible, to avoid complications from furure leakage. If this is not
practical, earthenware pipes should be rephced by PVC and

Pilling chnald beef te soos eal pve cathe marooasdng soil

and compacted to the same density.

Except in areas where freezing of water is an issue, it is wise to

remove taps in the building area and relocate them well away from

the building — preferably noe uphill from it (see BTF 19).

Tt may be desirable to install a grated drain at the outside edge of the

paving on the uphill side of the building. If subsoil drainage is
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 subfloor and significantly slows the process of drying

Warning: Although this Building Technology File deals with
cracking in buildings, it should be said thar subfloor moisture can

result in the development of other problems, notably:

© Water that is transmiteed into masonry, metal or timber building
elements causes damage and/or decay to those elements.

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

© Where high moisture levels are transmitted to the flooring and
walls, an increase in the dust mite count can ensue within the
living areas. Dust mites, as well as dampness in general, can be a
health hazard to inhabitants, particularly those who are
abnormally susceptible to respiratory ailments.

The garden

The ideal vegetation layout is to have lawn oc plants that require only
light watering immediately adjacere to the drainage or paving edge,
then moce demanding plants, shrubs and trees spread our in thar order.
Overwatering due to misuse of automatic watering systems isa
common cause of saturation and water migration under footings. If ir
is necessary to use these systems, it is important to remove garden
beds to a completely safe distance from buildings.

Existing trees

Where a tree is causing a problem of soil drying or there is the
existence or threat of upheaval of footings, if the offending mots are
they should be severed and a concrete or metal barrier placed
vertically in the soil to prevent furure root growth in the direction of
the building, If it is not possible to remove the relevant roots without
damage to the tree, an application to remove the teee should be made
to the local authority. A prudent plan is to transplant likely offenders
before they become a problem.

Information on trees, plants and shrubs

State departments overseeing agriculture can give information
regarding root patterns, volume of water needed and safe distance
from buildings of most species. Botanic gardens are also sources of
information. For information on plant roots and drains, see Building
Technology Pile 17.

Excavation

Excavation around footings must be properly engineered. Soil
supporting fooeings can only be safely excavated at an angle that
allows the soil under the footing to remain stable. This angle is called
the angle of pose (or fiction) and varies between soil
types and conditions. Removal of sail within the angle of repose will
cause subsidence.

Where erosion has occurred that has washed away soil adjacent to
footings, soil of the same classification should be introduced and
compacted to the same density. Where footings have been
undermined, augmentation or other specialist work may be required.
Remediation of footings and foundations is generally the realm of a
specialise consultant.

Where isolated footings rise and fall because of swell/shrink effect,
the homeowner may be tempeed to alleviate floor bounce by filling
the gap thar has appeared between the bearer and the pier with
blocking. The danger here is that when the next swell segment of the
cycle occurs, the extra blocking will push the floor up into 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 FAIB, MIAMA, Partner,
Construction Diagnosis.

‘The Information In this and other Issues in the series was derived from various sources and was belleved to be correct when published.

 

‘The Information ts advisory. Its provided In good falth and not claimed to be an exhaustive treatment of the relevant subject.

 

Further profossional advice needs to be obtained before taking any action based on the Informatkn promded.

 

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