Slope Stability Report (rec. 16.04.25) · MCU25/0042

TABLE 2. CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS.

Description of typical damage and required repair

Hairline cracks
Fine cracks which do not need repair
Cracks noticeable but easily filled. Doors and windows stick slightly.

Cracks can be repaired and possibly a small amount of wall will need to be replaced. Doors and

windows stick. Service pipes can fracture. Weathertightness often impaired.

Extensive repair work involving breaking-out and replacing sections of walls, especially over doors
and windows. Window and door frames distort. Walls lean or bulge noticeably, some loss of

bearing in beams. Service pipes disrupted.

Approximate crack width limit Damage category
<0.1mm 0—Negligible
<imm 1—-Very Slight
<5mm 2-Slight

5-15 mm (or a number of cracks 3 mm 3— Moderate

or more in one group)

15-25 mm but also depends onnumber 4 - Severe

of cracks

Source: Reproduced with the permission of Standards Australia Limited © 2011. Copyright in AS 2870-2011 Residential slabs and footings vests in Standards Australia Limited.

Warning: Although this Building Technology Resource deals with
cracking in buildings, it should be said that subfloor moisture can
result in the development of other problems, notably:

>» Water that is transmitted 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,
and mould.

> 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 or plants that require
only light watering immediately adjacent to the drainage or paving
edge, then more demanding plants, shrubs and trees spread out in
that order.

Overwatering due to misuse of automatic watering systems is a
common cause of saturation and water migration under footings.
If it 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 roots
are subsidiary and their removal will not significantly damage
the tree, they should be severed and a concrete or metal barrier
placed vertically in the soil to prevent future 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
tree 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.

Garden bed covered
with mulch

Tree height selected for
nce from house

Drained pathway

© Medium
Q height
oO

Shrubs oo

Carport Path Driveway

 

FIGURE 2 Gardens for a reactive site.

EXCAVATION

Excavation around footings must be properly engineered. Soil
supporting footings 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 repose (or friction) and varies significantly
between soil types and conditions. Removal of soil within the
angle of repose will cause subsidence.

REMEDIATION

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 specialist consultant.

Where isolated footings rise and fall because of swell/shrink effect,
the home owner may be tempted to alleviate floor bounce by filling
the gap that 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 it is necessary to use blocking, it should be by a pair of fine
wedges and monitoring should be carried out fortnightly.

@ CSIROPUBLISHING

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