Avocet Pde OPW - App E Slope · OPW20/0092

AUSTRALIAN GEOGUIDE LR3 (LANDSLIDES IN SOIL)

Landslide due to poorly supported excavation,
excassive fill depth, steep excavated

 

Figure 3
Some of the more common causes of landslides in soil are:
1) Falls of the parent material or residual sol from above, due to natural weathering processes (Figure 2).

2) Increased moisture content and consequent softening of the soil, or a rise in the water table. These can be due
to excessive tree clearance, ill-considered soak-away drainage or septic systems, or heavy rainfall (Figure 2).

3) Excavation without adequate support, increased surface load from fill placement, or inadequately designed
shallow foundations (Figure 3).

4) Natural erosion at the toe of the slope due to scour by a river or the sea (Figure 3).

5) Reactivation of an ancient landslide (Figure 3).

Most soil slopes appear stable, but they af achieved their present shape through 3 process of weathering and erosion

and are often sensitive to minor changes in the factors that affect their stability. As a general rule, human activities only

improve the situation if they have been designed to do so. Once this idea is understood, @ is probably easy to see why

the following basic mules are so important anc should not be ignored without seeking site specific advice from a

geotechnical practiboner:

. Do not clear trees unnecessarily.

. Do not cut into a slope without supporting the excavated face with an engineer designed structure.

. Do not ade weight to a slope by placing earth fil or constructing buildings with madequately designed shallow
foundations (Note: in certain circumstances weight is added to the toe of 3 slope to inhibit landslide movement.
but this must be carried out in accordance with a proper engineering design).

- Deo not allow water from storm water drains, or Tom septic waste or effluent disposal systems to soak into the
ground where it could trigger a landside.

More information in relation to good and poor hillside constructon practice is given in GeoGuiee LR8. With appropriate

engineering input it is often possible to reduce the likelihood. or consequences, of a landslide and so reduce the risk to

Property and to life. Such measures can include the construction of properly designed storm water and sub-sol drains,

surface protection (GeoGuide LR5) and retaining walls (GeoGuide LR6). Design should be undertaken by a
nical itioner and will normal ire local council wal

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

GeoGuide LR1 - Introduction
GeoGuide LR2 - Landsides
GeoGuide LR4 - Landslides In Rock
GeoGuide LRS - Water & Drainage
GeoGuide LR - Retaining Walls

GeoGuile LR7 - Landslide Risk

GeoGuie LRS = - Hillside Construction

GeoGuide LRS - Effiuent & Surface Water Disposal
GeoGuide LR10 - Coastal Landsiides.

GeoGuide LR11 - Record Keeping

 

The Ausvallan GeoGuides (LR series) we a set of publications intended for propeny owners; loca? councils, planning authorities;
Developers; insurers; lawyers and. in fact, anyone whe llvee with, or has an interest in, a natural or engmeeres slope, a cutting of an
excavation. They are intended to ne!p you understand why slopes and retaining structures can be a hazard and what can be cone with
aporoprate professional advice and Iocal counc? aporoval (fF required) fo remove, reduce, or minimise the ne& they represent. Tne
GeoGuiles have deen prepared by ine Australian Geomechanics Society. a speciatsi tecnnkca’ society within Engineers Ausiralla, the
natonal peak body for all engineering @scpiines in Australia, whose members are professiona’ gectecnnica engmeers and engineering
geologisis with 3 particular interest in ground engineering. The GeoGuides have been funded under the Australian governments’
Natona Disaster Mitigation Program.

Australian Geomechanics Vol 42 No 1 March 2007 165