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More and more natural disasters are being reported worldwide, particularly with respect to landslides. They cause injuries and deaths and induce physical, environmental and economic damages that hamper the development of wealthy as well as poor countries and regions. It is therefore necessary to include consideration of landslide hazards in land use and emergency response planning for public safety and realization of safe engineering projects. It is essential for authorities to have appropriate maps describing hazardous areas at their disposal. It is also important that they are aware of the different steps within a coherent approach that lead to the identification of landslide areas, the evaluation of the corresponding hazards, and the assessment of the risks these assessments imply. A large number of distinctive methods for landslide hazard mapping have been tested and applied in different contexts for more than 30 years. Many of them have been presented in recent international conferences such as the International Symposium on Landslides (Rio de Janeiro, 2004), the International Conference on Landslide Risk Management (Vancouver, BC, 2005), or the International Forum on Landslide Disaster Management (Hong Kong, 2007), all of them organized under the auspices of the JTC-1, the joint ISSMGE, IAEG and ISRM Technical Committee on Landslides and Engineered Slopes. The JTC-1 recognizes that there is a need for unified terminology in susceptibility, hazard and risk zoning, so that zoning in any area could be compared on a similar basis with zoning of adjacent areas, and to insure that fundamental assessment steps are properly considered and applied in the management of landslide-prone areas. JTC-1 also recognizes that the time has now been reached when quantitative hazard and risk zoning is possible. With this in mind, JTC-1 appointed a Scientific Committee to undertake the development of guidelines for landslide susceptibility and hazard and risk zoning for land use planning with the requirement that the committee produce guidelines that are acceptable to the international community. A first draft in this complex process was developed by the Scientific Committee using as a starting point a document prepared by the Australian Geomechanics Society. This draft was discussed and its applicability was tested within an international group of 40 experts (listed at the end of the preface) most of whom met for a workshop in Barcelona from September 18 to 20, 2006. This very fruitful workshop proved to be a forum for vigorous debate, and many helpful suggestions arose on how to improve the guidelines. Many of these suggestions have been included in the Commentary appended to the Guidelines. There were numerous additional suggestions (which were not included in the interest of balance and because of space restrictions) and a large number of formal corrections that were important to improve the quality of the guidelines. A set of accompanying papers have been also included in this special issue of Engineering Geology. These pa...

Six percent of Switzerland is prone to slope instability. New federal regulations require regional authorities (cantons) to generate natural hazard maps and the zoning of mass movements in order to restrict development on hazard-prone land. The Codes of Practice for hazard maps use red, blue and yellow respectively, to indicate areas of prohibited construction, construction with safety requirements and construction without restriction. They need considerable efforts to ensure communication with local populations. The present state of landslide hazard mapping in the 26 cantons, the transcription of hazard maps to local management plans and the corresponding rules are presented.

Thanks to a sophisticated transient hydrogeological modelling allowing the determination of the pore pressure fields in La Frasse landslide mass during a crisis, it has been possible to model the mechanical behaviour of the slide and obtain results that prove to be similar to the monitored data, in terms of peak velocity, distribution of velocity with time and space and total displacements. Such results are reached only when appropriate constitutive modelling laws are used, and when geotechnical tests supply all the required parameters. The main results concern the potential effect of a drainage system during a crisis, like the one experienced in 1994. It can include vertical boreholes equipped with pumps or drains drilled from a gallery. The draining system reduces horizontal displacements down to 5% of the values modelled during the crisis. This effect, which appears to extend over a large width, will be even more significant if the boreholes discharge the drained water into the gallery, due to its extension in the presently stabilised landslide mass below the active zone. The modelling tools developed for La Frasse landslide thus provide all the necessary information to optimise the drainage scheme.

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