Response to Information Request - MCU12/0184

                       AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)

                   EXAMPLES OF POOR HILLSIDE CONSTRUCTION PRACTICE


                                                                                           Vegetation removed
                                                                   Steep unsupported cut fails
                           Discharges of roofwater soak away rather than
                           conducted Qffsite or to ’secure storage for re-use

                                         Structure unable to tolerate
                                         settlement and




                            Inadequate w lling unable
                            to support


                           Inadequately
                           supported cut fails


                                                                                                                  Dwelling not founded in
                                                                                                                  bedrock




                                                                                                    Loose, saturated fill slides and
                                                                                                    possibly flows downslope
                                                          Ponded water enters slope and activates landslida
                                                                                                                                     @AGS(2007)
                                            travel downslope which impacts other development downhill                 See .Iso AGS (2000)Appendix J
                                                    ...




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 effluent 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:

         GeoGuide LR1           -
                                    Introduction                                         GeoGuide LR6         -
                                                                                                                  Retaining Walls
         GeoGuide LR2           -
                                    Landslides                                           GeoGuide LR7         -
                                                                                                                  Landslide Risk
         GeoGuide LR3           -
                                    Landslides in Soil                                   GeoGuide LR9         -
                                                                                                                  Effluent & Surface Water Disposal
         GeoGuide LR4           -
                                    Landslides in Rock                                   GeoGuide LR10        -
                                                                                                                  Coastal Landslides
         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.




                                     Australian Geomechanics Vol 42 No 1 March 2007                                                                   175