MECHANISM OF SLOPE FAILURE DURING HEAVY RAINFALL IN NAGASAKI JULY 1982

On July 23,1982,299 human lives were lost in Nagasaki Prefecture due to localized heavy rainfall, nearly 90% of which were due to sediment disaster. So, it is important to clarify a mechanism of slope failure during heavy rainfall for sediment disaster prevention. In this paper, we firstly carry out a model experiment of slope failure due to infiltration and observe a phenomenon in progressive failure of slope. Secondly, we apply a finite element analysis which is divided into two stages, i.e. a saturated-unsaturated seepage flow analysis and a stability analysis taking into account the seepage force and the reduction of strength due to the rise in the degree of saturation, to two actually failured slope in Nagasaki city. And we check their failure under the conditions of preceding rainfall, rainfall on the day of failure, topography, geology and so on. Finally, we have clarified a mechanism of slope failure during heavy rainfall and shown that slope failure can be predicted if a rise in the groundwater table can be detected