Veins of groundwater flow relating to slope failures in layer of colluvium at crystalline schist area

Abstract

During the heavy rain on June 29, 1999, four slope failures occurred around the Taishi-do area in Zentoku landslide, Tokushima, Japan. Based on field investigation after these failures, and the monitored records of the three-dimensional shear displacement me-ters before the failures, it was made clear that 1) the failures were limited comparing to the rainfall ; 2) One of the failures showed precursory displacement of creeping failure. To clarify the failure mechanism, field investigations including one-meter depth of soil temperature survey, temperature measurements of spring water and groundwater in borehole were conducted, and pore water pressures generated at failure were estimated through back-analysis. Thereafter, the relationship between the location of failed slopes and flowing groundwater veins, and the relationship between groundwater vein and precursory displacement of failures were analyzed. It is found that: 1) Slope failure occurred above or near groundwater vein ; 2) There were two types of groundwater veins, one was surficial vein type with high water temperature, and the other was deep vein type originating from a depth between 49 and 70m with low water temperature ; 3) The precursory displacement of the creeping failure was associated with the groundwater vein.