Journal of Natural Disaster Science

INVESTIGATION OF RAINFALL-INDUCED PORE PRESSURES IN NATURAL SLOPES

Naftali, S. MSHANA
Graduate Student, Department of Environmental science, Kumamoto University
Atsumi SUZUKI
Professor, Civil and Environmental Engineering Department, Kumamoto University
and
Yoshito KITAZONO
Associate Professor, Civil and Environmental Engineering Department, Kumamoto University

(Received 23 April 1992 and in revised form 13 October 1993)

Abstract

A study of rainfall-induced pore pressures in a natural slope of weathered, unwelded tuff soil is reported. A comparison of observed field and estimated pore pressures showed that the base of the natural slope was permeable rather than impermeable, therefore the permeable base was modelled taking into account the interface between the soil and the weathered base rock and considering it to be a seepage face boundary.

Based on long term observations of soil suction, field dewatering parameters and corresponding nomograms are developed. Nomograms which consider weather information including antecedent rainfall at the particular time of analysis, are useful in estimating initial pore pressures as input for finite element analysis.

As an example, pore pressures caused by the disastrous rainfall observed during the 23 July 1982 slope failure disaster were estimated for this particular slope based on initial conditions as estimated from the dewatering nomograms. Results show that saturated zones with very low pore pressures developed at the base of the soil layer; evidence of the effectiveness of the modelling process used.

Key words

pore pressure, rainfall, seepage, weathering, finite element analysis, ground water, saturation