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ANALYSIS OF SLOPE GRADIENT ANTECEDENT TO LANDSLIDE FOR PRIMARILY SLIDE SUSCEPTIBILITY MAPPINGS
Tetsuya KUBOTA
Environment Science Department Faculty of Agricolture, Tottori University, TOTTORI, 680, JAPAN E-mail:kubot@agr.tottori-u.ac.jp
Mapping of the areas with unstable slope is important to decide the priority of slope stabilization works, as well as to plan warning and evacuation for residents, railroads, highways etc. In this situation, topographical factors have been adopted to investigate landslide susceptibility with geological and meteorological ones. In this study, "Slope gradient antecedent to landslide" is proposed as an index in susceptibility investigation for primarily slides which are up to certain percentage of landslides (40% in Japan). In this context, it is necessary to know the slope angle, antecedent and after the slide. Hence, antecedent slope angle q and post-slide angle q 0 are investigated for several landslides, including some historic ones that were restored using "Critical Slip Surface Analysis by Dynamic Programming (CSSDP)", historical records, geological knowledge. The CSSDP can search the critical slip surface that has minimum factor of safety (Fs) in given slope structures. Consequently, the slope ratio q 0/q of 0.8 <= G <= 0.9 was gained as average values for all geology. It is important information to detect the susceptible slope relevant to primarily landslides.
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