Approved Plan - EXE230029

                                               AUSTRALIAN GEOGUIDE LR2 (LANDSLIDES)
            What is a Landslide?

            Any movement of a mass of rock, debris, or earth, down a slope, constitutes a “landslide”. Landslides take many forms, some of
            which are illustrated. More information can be obtained from Geoscience Australia, or by visiting its Australian landslide Database
            at www.ga.gov.au/urban/factsheets/landslide.jsp. Aspects of the impact of landslides on buildings are dealt with in the book
            “Guideline Document Landslide Hazards” published by the Australian Building Codes Board and referenced in the Building Code of
            Australia. This document can be purchased over the internet at the Australian Building Codes Board’s website www.abcb.gov.au.

            Landslides vary in size. They can be small and localised or very large, sometimes extending for kilometres and involving millions of
            tonnes of soil or rock. It is important to realise that even a 1 cubic metre boulder of soil, or rock, weighs at least 2 tonnes. If it falls,
            or slides, it is large enough to kill a person, crush a car, or cause serious structural damage to a house. The material in a landslide
            may travel downhill well beyond the point where the failure first occurred, leaving destruction in its wake. It may also leave an
            unstable slope in the ground behind it, which has the potential to fall again, causing the landslide to extend (regress) uphill, or expand
            sideways. For all these reasons, both “potential” and “actual” landslides must be taken very seriously. The present a real threat to
            life and property and require proper management.

            Identification of landslide risk is a complex task and must be undertaken by a geotechnical practitioner (GeoGuide LR1) with specialist
            experience in slope stability assessment and slope stabilisation.

            What Causes a Landslide?

            Landslides occur as a result of local geological and groundwater conditions, but can be exacerbated by inappropriate development
            (GeoGuide LR8), exceptional weather, earthquakes and other factors. Some slopes and cliffs never seem to change, but are actually
            on the verge of failing. Others, often moderate slopes (Table 1), move continuously, but so slowly that it is not apparent to a casual
            observer. In both cases, small changes in conditions can trigger a landslide with series consequences. Wetting up of the ground (which
            may involve a rise in groundwater table) is the single most important cause of landslides (GeoGuide LR5). This is why they often
            occur during, or soon after, heavy rain. Inappropriate development often results in small scale landslides which are very expensive
            in human terms because of the proximity of housing and people.

            Does a Landslide Affect You?

            Any slope, cliff, cutting, or fill embankment may be a hazard which has the potential to impact on people, property, roads and
            services. Some tell-tale signs that might indicate that a landslide is occurring are listed below:

                 Open cracks, or steps, along contours                          trees leaning down slope, or with exposed roots
                 Groundwater seepage, or springs                                debris/fallen rocks at the foot of a cliff
                 Bulging in the lower part of the slope                         tilted power poles, or fences
                 Hummocky ground                                                cracked or distorted structures

            These indications of instability may be seen on almost any slope and are not necessarily confined to the steeper ones (Table 1).
            Advice should be sought from a geotechnical practitioner if any of them are observed. Landslides do not respect property boundaries.
            As mentioned above they can “run-out” from above, “regress” from below, or expand sideways, so a landslide hazard affecting your
            property may actually exist on someone else’s land.

            Local councils are usually aware of slope instability problems within their jurisdiction and often have specific development and
            maintenance requirements. Your local council is the first place to make enquiries if you are responsible for any sort of development
            or own or occupy property on or near sloping land or a cliff.

            TABLE 1 – Slope Descriptions
                                              Slope         Maximum
                Appearance                    Angle         Gradient        Slope Characteristics
                Gentle                       0 - 10        1 on 6         Easy walking.
                Moderate                     10 - 18       1 on 3         Walkable. Can drive and manoeuvre a car on driveway.
                Steep                        18 - 27       1 on 2         Walkable with effort. Possible to drive straight up or down roughened
                                                                            concrete driveway, but cannot practically manoeuvre a car.
                Very Steep                   27 - 45         1 on 1       Can only climb slope by clutching at vegetation, rocks, etc.
                Extreme                      45 - 64        1 on 0.5      Need rope access to climb slope.
                Cliff                        64 - 84        1 on 0.1      Appears vertical. Can abseil down.
                Vertical or Overhang        84 - 90        Infinite      Appears to overhang. Abseiler likely to lose contact with the face.


            February 2019



Document Set ID: 22532435
Version: 1, Version Date: 07/08/2023