Abstract
A complicated shape of underground slide surface is presumed by the analysis of displacement vector of ground objects observed in the landslide area. The vector that is considered to represent the movement of sliding mass is obtained by three dimensional surveying such as the field total station method or the aerial photogrammetry. On a vertical projection plane parallel to the direction of landslide movement, the shape of underground slide surface is estimated by the following procedure. First, each set of grouped vectors are analyzed by the procedure of least square or analytic geometry to find their rotational center on the projection plane. Next, using the series of rotational center points, a compound curve conformable to the landslide is constructed by interconnection of arcs having various radii. And next, safety factor of the compound curve considered as possible slide surface is estimated. Several compound curves obtained by various displacement vector grouping are evaluated by the conformity with the landslide phenomena and by the corresponding safety factor. Finally, the most reasonable shape of the underground slide surface is presumed. A numerical example is shown for analysis of the Narao-landslide occurred at the north-western region in Nagano prefecture, Japan.
