Avocet Pde OPW - App E Slope · OPW20/0092

AUSTRALIAN GEOGUIDE LR5 (WATER & DRAINAGE)

 

Figure 2 - Techniques used to control groundwater flow

Surface water drains (dish drains, or table drains) - are often used to prevent scour and limit inflow to a slope. Other
than in rock, they are relatively ineffective unless they have an impermeable lining. You should clear them regularly, and
@s required, anc not less than once a year. ff you live in an area with seasonal rainfall, it is best to do this near the end
of the dry season. If you notice that soil or rock debris is falling from the slope above, determime the source and take
a@ppropnate action. This may mean you have to seek advice from a geotechnical practitioner.

Surface protection - is sometimes used in addition to surface water drainage to prevent scour and minimise water
inflow to a slope. You should inspect concrete, shotcrete or stone pitching for cracking and other signs of deterioration at
least once a year. Make sure that weepholes are free of obstructions and able to drain. If the protection is deteriorating.
you should seek advice from a geotechnical practitioner.

Sub-soil drains - are often constructed behind retaining walls and on hillsides to intercept groundwater. Their function is
to remove water from the ground through an appropriate outlet. {t is important that subsoil drains are designed to
complement other measures being used. They should be laid in a sand, or gravel, bed and protected with a graded
stone or geotextile filter to reduce the chance of clogging. Sub-sol drains should always be laid to a fall of at least 1
vertical on 100 horizontal. Ideally the high end should be brought to the surface, so it can be flushed with water from
time to time as part of routine maintenance procedures.

Deep, underground drains - are usually only used in extreme circumstances, where the landslide nsk is assessed as
not being tolerable and other stabilisation measures are considered to be impractical. They work by permanently
lowering the water table in a slope. They are not often used in domestic scale developments, but if you have any on your
site be aware that professional maintenance is essential. {f they are not maintained and stop working, the water table will
rise and a landslide may even occur during normal weather conditions. Both an increase or a reduction in the normal
flow from deep drains could indicate a problem if it appears to be unrelated to recent rainfall. If changes of this sort are
observed, you should have the draims and your site checked by a geotechnical practitioner.

Documentation - design drawings and specifications for geotechnical measures intended to minimise landslide nsk can
be of great assistance to a geotechnical specialist, or structural engineer, called in to inspect and report on them. Copies
of available documentation should be retained and passed to the new owner when the property is sold (GeoGuide
LR11). You should also request details of an appropnate maintenance program for drainage works from the designer
and keep that information with other relevant documentation and maintenance records.

More information relevant to your particular situation may De found In other Austrailan GeoGuides:

© GeoGuide LRi - Introduction GeoGuide LR7 - Landslide Risk

GeoGuide LR2 -Landsides GeoGuide LR& = - Hillside Construction

GeoGuide LR3 - Landsides in Soll GeoGuide LRS -EMuent 4 Surface Water Disposal
GeoGuide LR4 -Landsides In Rock GeoGuide LR10 - Coastal Landsiides

GeoGuide LR6 - Retaining Was * GeoGuide LR1I1 - Record Keeping

The Australian GeoGuides (LA serles) ae a set of publications intended for propeny owners, local councils, planning authorities,
Gevelopers: Insurers: lawyers and. im fact, anyone who live with, of has an interest in, a natural or engineered slope. a cutting. or an
excavaton. They are intended to help you understanc why slopes and retaining structures can be a hazard and what can be done with
appropriate professional advice and local council aporoval (f required) to remove. reduce, or minimise the ns& they represent. Tne
GeoGuides Nave deen prepared by the Australian Geomechanics Society a specialist technica society within Engineers Australia, tne
national peak body for all engineering aiscpiines in Australia, whos members are professiona’ geotechnical engineers and engneering
a wth 3 particular interest in ground engineering. The GeoGuides nave been funded under the Austraian govemments’
Nationa’ Disaster Miagation Program.

 

Australian Geomechanics Vol 42 No 1 March 2007 168