Journal of Natural Disaster Science

Geotechnical Features of the Hachimantai-Sumikawa Landslide

Eiji YANAGISAWA
Graduate School of Civil Engineering, Tohoku University
and
Jun UMEMURA
College of Engineering, Nihon University

(Received 30 November, 1998 and in revised form 5 April, 1999)

Abstract

An outline of a landslide that occurred at Sumikawa Spa, Hachimantai, Akita Prefecture is given, and its cause discussed on the basis of results of a geotechnical investigation. From the stability analysis, the apparent strength parameters, c and j, of a cross section of a major sliding block are estimated respectively to be about 40 kPa and about 6 degrees. The effect of sliding of the lower block on the stability or the upper block also was examined. The shear strengths of the slip surface clays, determined by box shear tests are similar for the disturbed and undisturbed states, and the strength parameter j' becomes approximately 13.5 degrees. All remolded specimens of the slip surface clays show an increase in shear resistance in the larger strain after peak, whereas there is softening behavior for the undisturbed samples. The residual strength of undisturbed samples therefore could be used for the stability analyses, because it gives a safety side result. Although there is a slight difference between the estimated and tested strengths, the estimated values of the strength parameters are concluded to be appropriate for the design of countermeasures to stabilize sliding blocks against landslides.

Key words

landslide, stability analysis, shear strength, undisturbed sample