Abstract
The years of 2004 and 2005 had many slope failures in Japan. Those failures were caused by heavy rainfalls and the 2004 Niigata-Chuetsu earthquake. It was thought to be important in such a situation to examine the validity of existing hazard assessment methodologies concerning slope failures. Site visits were therefore made at those failed slopes, and soil samples were collected. With a special attention focused on the effects of water on mechanical properties of soils, plasticity index and swelling tests were conducted on those soils as well as triaxial compression tests on dry and water-submerged remoulded specimens. The water effects on mechanical properties of soils were accelerated to occur for experimental purposes by grinding soil particles and increasing their surface area. It was concluded that the existing hazard assessments are basically reasonable. It was shown, however, that they can be improved so that the extent of damage such as the run-out distance of sliding soil mass may be assessed by further taking into account the physical properties of soils.
