Landslide Risk Management Concepts And Guidelines

Slope instability occurs in many parts of urban and rural Australia and often impacts on housing, roads, railways and other development. This has been recognised by many local government authorities, and others, and has led to preparation of a number of landslide hazard zoning maps for specific areas, and to the requirement by many local government councils for stability assessments prior to allowing building development. Many such assessments have been based on the paper “Geotechnical Risk Associated with Hillside Development” (Walker et al, 1985) which was written by a subcommittee of the Australian Geomechanics Society Sydney Group.

That paper presented a risk classification for slope instability for use in the Sydney Basin (Newcastle-Sydney- Wollongong-Lithgow). It was intended for use by geotechnical consultants, to foster uniformity in the description of risk.

It has become apparent that there are significant deficiencies in the 1985 approach, including:

• The terms are poorly defined
• There was no quantification of risk
• There was no consideration of the potential for loss of life
• The emphasis was on the impact of landsliding occurring on the property to be developed, and did not sufficiently emphasise the importance of landsliding from slopes above a property
• The method was developed for the Sydney Basin and does not necessarily apply to other geological environments.

Even within the Sydney Basin there were difficulties in applying the method to areas where very large ancient landslides may be present (e.g. in Wollongong and Newcastle), and to some rock slope situations.

In recognition of this, the National Committee of the Australian Geomechanics Society set up a sub-committee to review what was needed, and establish new guidelines. During this process it became apparent that there is a need for guidance to help practitioners carry out stability assessments for housing allotments, and for use more widely in slope engineering, using risk assessment procedures.

The purpose of this guideline is:

• to establish a uniform terminology;
• define a general framework for landslide risk management;
• provide guidance on methods which should be used to carry out the risk analysis;
• provide information on acceptable and tolerable risks for loss of life.

Such guidelines also have a role in explaining to the public, regulators and the legal profession the process and limitations of Landslide Risk Management.

It is recommended that practitioners and regulators cease using the methods described in Walker et al (1985), and follow these guidelines.