In Tertiary strata men, plane slip along weak strata is predominated as the slope failure has several patterns, and it may cause instable trouble in cutting slope frequently. The relationship between the strike and dip of strata and orientation of slope is much important and controls the plane slip patterns. The slope stability assessment method is different from circular failure analysis. In addition, for evaluating slope stability, usually two-dimensional assessment is adopted whereas, it should be carried out in three dimensions. Especially, when inclination of strata differs from slope inclination, three-dimensional analysis is indispensable. In this paper, taking a certain section along Western Kyushu Expressway (Takco-Sascbo) as study object, a database related to slope stability management has been established by using Geographic Information System (GIS) in Tertiary strata area. By combining stereo-net method with GIS raster model, slope stability along the expressway has been assessed, and the slope stability distribution maps have been accomplished, and the potential slide area zoning and configuration of slide are evaluated.
The Western Kyushu Expressway has been constructed and occupied in use connecting with Saga and Nagasaki Prefecture Japan since 1990. Some slope failures had taken place on cutting slope especially during the construction stages. Most of slope failure patterns are plane slip along weak strata in this area since the Expressway passes through Tertiary strata. Therefore, an efficient tool for the database information management and slope stability analysis is necessary. GIS combined with stereo-net method has been used as the tool of this study. In this study, multilayer digital map has been created. The strike and dip of both rock strata and slope, which are stored as the grid (pixel) value of GIS raster model, have been used to assess the roadsides slope stability automatically by using GIS Avenue program. As the final results, slope stability evaluation map and the potential slide area-zoning map are created.
The topographic along Western Kyushu expressway are relatively flat hilly area in Cenozoic Era Palaeogene Period area. The nature slopes are roughly 8 15 degree, the erosion is serious markedly on valley foot. So the valley is narrow and with many sub valleys. In this area the Paleogene Kishima Group is extensively distributed, and is constituted by sand stone, sandy shale and shale. In some regions weathering tuff is interposed between these layers. The geological structure inclination is about NW5 10 degree in monocline. In the past, crust movement was experienced in this area, and faults were appeared everywhere. This expressway involves 266 locations of cutting slope and 57 slope failures, about 20% of total cutting slope, occurred during the construction period. Most of the slides are initial slope failures of the bare rock(Hitosi, 1991).
In the recent years, GIS, with its excellent spatial data process Ability, has attracted great attention in natural disasters assessment (Terlien, 1996). GIS is a system of hardware, software for data capture.
