Geotechnical In-Situ Technology (GIST) Network Development of real-time GIS tools for interpreting slope instability from geo-databases

Abstract

Slope stability hazard assessment is generally based on an understanding of the expected slope failure mechanism, and the strength of the soil and rock materials under different moisture conditions. Slope stability may be reduced by factors external to the slope, including earthquake loading and modifications to the slope geometry, either by human activities or natural erosion processes. Stability analysis may be based on regional or more localized approaches, both of which may be based in development and analysis of a geo-database. On a regional scale, assessment is based on analysis of surface data, including geomorphological evidence of pre-existing or ongoing slope failures, slope angle, distribution of surficial geology, vegetative cover and precipitation. Assessment of the relative importance of these factors is based on understanding the slope failure mechanisms. Geospatial analysis tools have been implemented in GIS programs to assess the relative likelihood of slope instability and to create slope hazard maps. On a local scale, assessment of slope instability may be based on the results of geotechnical instrumentation of the surface and sub-surface materials. For complex, heavily instrumented slopes, compilation of the relevant information, including slope movement, piezometric pressure, precipitation and temperature, into a geo-database is required. Analysis of the information collected, coupled with parametric analyses of slope instability using numerical simulation tools, is required to assess the potential for slope instability. These analyses generally result in a quantitative assessment of instability in the form of factor of safety or probability of failure. Case history examples of the application of GIS tools written for analysis of slope instability at both the regional and local scale will be provided in this paper. At the regional scale, analysis of the potential for instability of sensitive clay slopes along river valleys resulting in slope hazard maps will be presented. At the local scale, the development of a GIS platform for analysis of geotechnical data and provision of early warning based on analysis of multiple geotechnical sensors will be discussed. The application of this approach to analysis of a heavily instrumented, potentially unstable slope located on the banks of a hydropower reservoir, just upstream of the dam, will be discussed.