Slope failures in residential land on volcanic fills during the 2011 Great East Japan earthquake

摘要

As a result of the 2011 off the Pacific coast of Tohoku Earthquake, five slope failures occurred in a residential area on artificial valley fills in Taiyo New Town, Yamamoto, Miyagi Prefecture. The fill material is sandy, derived from the weathering of tuffaceous sandstone which formed the natural ground. Cyclic triaxial tests showed that the fill, which has about F_c = 20%, has very low liquefaction resistance, which decreased with application of initial static shear stress. A pseudo-static slope stability analysis, using conventional strength parameters, could not explain the slope failure at one of the sites that failed, but it could explain the slope failure when the dynamic strength was used to represent the soil strength at the slip surface. Thus, the slope failures in Taiyo New Town, at least at the one analyzed in this study, could be attributed to the liquefaction of the fill material induced by the intense shaking.