An Investigation into the Effect of Drainage on Large Slope Failure During Earthquakes

Abstract eng:
A lot of large, long-distance landslides occurred due to a big earthquake in Japan, called the 2004 Mid Niigata Prefecture Earthquake. One of these landslides occurred when a slope composed of mudstone debris failed. Slopes composed of mudstone debris have been thought to be seriously damaged by rainfall but not so seriously by earthquakes. Sampling of several intact soil blocks was done at the landslide site and the cyclic tri-axial tests on the specimens were performed under undrained conditions in a laboratory. These experimental results suggested that the cause of the failure was possibly a rapid increase of the pore water pressure inside the mudstone due to the cyclic shear during the earthquake. That is, this rapid increase of the pore water pressure made the safety factor of the slope drop considerably below 1.0, which triggered the large, long-distance landslide. We assumed the groundwater level at the time of the earthquake from the field investigation and calculated the safety factor of the large slope failure by limit equilibrium method. The groundwater level was calculated by seepage analysis (finite element method) after the drains were installed and their effect on the stability evaluated by limit equilibrium method.

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