Slope Stability Report

AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)
EXAMPLES OF POOR HILLSIDE CONSTRUCTION PRACTICE

Unstabilised rock topples and travels dawnsiope
‘Vegetation removed ——
‘Steep unsupported cut fails
Discharges of roofwaler soak away rather than
conducted offsite of to secure storage for re-use
‘Structure unable to tolerate
setternent and cracks:

Poorly compacted fill setties
unevenly and cracks pool

 
 
  
 
  
 
 
 
 
 
 
 
    
  

Inadequate walling unable
to support fill
inadequately
supported cut fails
Saturated \
slope fais — z ~ Dwelling not founded in
’ bedrock

Absence of subsoil drainage
within fill

Loose, saturated fill slides and
possibly flows downslope
—— Ponded water enters slope and activates landslide
(@ Ags @oor)

NS hie eal Gee DOE Pees chet cise doo ‘Bee alse KIS (2000) Appendix
WHY ARE THESE PRACTICES POOR?

Roadways and parking areas - are unsurfaced and lack proper table drains (gutters) causing surface water to pond and
soak into the ground.
Cut and fill - has been used to balance earthworks quantities and level the site leaving unstable cut faces and added
large surface loads to the ground. Failure to compact the fill properly has led to settlement, which will probably continue
for several years after completion. The house and pool have been built on the fill and have settled with it and cracked.
Leakage from the cracked pool and the applied surface loads from the fill have combined to cause landslides.
Retaining walls - have been avoided, to minimise cost, and hand placed rock walls used instead. Without applying
engineering design principles, the walls have failed to provide the required support to the ground and have failed,
creating a very dangerous situation.
A heavy, rigid, house - has been built on shallow, conventional, footings. Not only has the brickwork cracked because
of the resulting ground movements, but it has also become involved in a man-made landslide.
Soak-away drainage - has been used for sewage and surface water run-off from roofs and pavements. This water
soaks into the ground and raises the water table (GeoGuide LR5). Subsoil drains that run along the contours should be
avoided for the same reason. If felt necessary, subsoil drains should run steeply downhill in a chevron, or herring bone,
pattern. This may conflict with the requirements for effiuent and surface water disposal (GeoGuide LR9) and if so, you
will need to seek professional advice.
Rock debris - from landslides higher up on the slope seems likely to pass through the site. Such locations are often
referred to by geotechnical practitioners as "debris flow paths”. Rock is normally even denser than ordinary fill, so even
quite modest boulders are likely to weigh many tonnes and do a lot of damage once they start to roll. Boulders have
been known to travel hundreds of metres downhill leaving behind a trail of destruction.
Vegetation - has been completely cleared, leading to a possible rise in the water table and increased landslide risk
(GeoGuide LR5).

DON'T CUT CORNERS ON HILLSIDE SITES - OBTAIN ADVICE FROM A GEOTECHNICAL PRACTITIONER

More information relevant to your particular situation may be found in other Australian GeoGuides:

 
 

e GeoGuide LR1 - Introduction « GeoGuide LR6 - Retaining Walls

e GeoGuide LR2 - Landslides @ GeoGuide LR7 - Landslide Risk

* GeoGuide LR3 - Landslides in Soil * GeoGuide LR - Effiuent & Surface Water Disposal
© GeoGuide LR4 - Landslides in Rock GeoGuide LR10 - Coastal Landslides

2 _GeoGuide LR5__- Water & Drainage « _GeoGuide LR11 - Record Keeping

 

The Australian GeoGuides (LR series) are a set of publications intended for property owners: local councils; planning authorities:
developers; insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an
excavation. They are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with
appropriate professional advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The
GeoGuides have been prepared by the Australian Geomechanics Society. a specialist technical society within Engineers Australia, the
national peak body for all engineering disciplines in Australia, whose members are professional geotechnical engineers and engineering
geologists with a particular interest in ground engineering. The GeoGuides have been funded under the Australian governments’
National Disaster Mitigation Program.