GEOTECHNICAL ASSESSMENT OF NATURAL SLOPES AND VALLEYS BASED ON REAL TIME RAINFALL DATA

Abstract

In monsoon periods, slope failures are major natural disasters in western Japan where most of
the areas are covered with weathered Granite (Masado) or weathered Rhyolite. The present hazard
assessment system available to predict such catastrophic events in the region is not adequate for early
evacuation purposes as it is not based on any reliable geotechnical assessments. To incorporate geotechnical
inputs and to enhance present risk assessment, this study was proposed and initially a method to determine
shear strength parameters was established. Authors have been already established a sound methodology and
relationships to determine shear strength parameters for weathered Granite and the present study focuses to
develop the same for weathered Rhyolite and to propose a method to evaluate real time factor of safety based
on real time rainfall data. A series of laboratory model tests based on lightweight dynamic cone penetrometer
and direct shear tests were conducted on weathered Rhyolite collected at Shobara city, Japan. Good graphical
relationships were developed with cone resistance, qd and void ratio e, void ratio e and apparent cohesion cd,
and void ratio e and internal friction angle φd. Stability analyses were conducted considering shear strength
parameters and the water table estimated based on real time rainfall data. It was found that the time of
occurring slope failures are well evaluated from the proposed method logy from this study. This study can be
extended to evaluate slope failures in forecasted rainfall conditions.