Att 3 - Landslide Risk Assessment

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WORKS AFTER TAKING POSSESSION
In some cases foundation conditions are changed
by the owner constructing new works such as:

*Constructing sheds or outdoor roofed areas
without connecting the roof drainage to storm
water lines.

*Constructing paving around the building without
sufficient slope away from the building. (In sandy
soils and low and moderate “reactivity” clays, a
slope of 1:40 up to 1 metre away from the
building is adequate. In highly reactive clays a
slope of 1:20 works better. In large paved areas
a drain and collection pit may be necessary).
(Fig. 5 & 18)

*Australian Standard 2870, “Residential Slabs
and Footings” requires soil drains and “normal”
soil garden moisture in M, H1, H2, E, and P sites
to be maintained by the owner. (Fig 10)

*Running machinery over shallow drain pipes
may break them causing leaks and subsequent
foundation movements.

*Any excavations close to building footings can
cause them to sink by disturbing the foundation
material or by drying the foundation clay. (Fig
11)

*Footings constructed in reactive clay sites during
wet periods may be damaged if the garden is
allowed to dry out excessively.

*Footings constructed in reactive clay sites during
dry conditions may experience damage if the
garden is watered unevenly or excessively.

5. LANDSCAPING AND TREES

Most modern allotments with clayey soils are too
small to safely grow large trees without special
footings. Generally the larger the root system of
the tree(s) the greater the drying effect. If in doubt
seek the advice of an expert arboriculturist and
designing engineer.

If you are about to build in a clay area and you
wish to grow, retain or remove trees near
buildings, the builder should be advised of this
prior to signing the building contract so that the
engineer can design for these conditions.

*Trees can cause damage during their life and
even for many months after their removal. If
they do not receive sufficient water while alive
their roots will dry the soil near buildings or
under pavements.

 

Fig. 8 Drainage concerns

 

 

 

 

 

 

Fig.9 Slab heave due to water ponding

 

Fig. 10 Soil Drainage Plan

RETAINING
WAL ——

 

 

Fig. 12 Damage due to soil moisture changes

 

 

 

 

Site Classification Report

 

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