2009 Volume 50 Issue 4 Pages 216-227
Infiltration of rainwater into slope surface is one of the fundamental factors for the occurrence of slope failures in monsoon regions. In addition to this, seepage water from the steep slope may also be an important factor because such seepage water changes depending on the infiltrated water from the upper horizontal surface, and sometimes it rapidly increases with rainfall. To understand these processes, the authors analyzed some fundamental data including continuous electric resistivity measurements, soil water, temperature and conductivity of seepage water from the slopes. A target slope is underlain by the Quaternary ignimbrites characterized by soft and permeable properties in southern Kyushu, Japan.
Apparent resistivity changes depending of rainfall with surface soil moisture. Based on the resistivity data measured during about one year, temporal changes of contents of water of the slope materials become rapidly and largely in the surface portion, whereas slow and small in the inner portion. These changes have a high correlation with the Antecedent Precipitation Index which was calculated from the daily rainfall and proper reducing coefficients. Then, applying these coefficients to the daily rainfall data for the day when many slope failures occurred, it may be possible to obtain a pattern of rainfall which bring about the occurrence of slope failures. If a proper unstable model and the influence of water contents to the safety factor Fs are obtained, it may be possible to predict the occurrence of slope failures on the basis of daily rainfall.
