Cyclic shear property and seismic runout analysis for pumice fall deposit

This paper presents the physical properties of pumice fall deposit sampled at Takanodai, Minami-Aso village, Kumamoto Prefecture in JAPAN, where long runout landslide took place due to the main shock from the 2016 Kumamoto earthquake. A series of direct box shear tests under various conditions such as constant-stress, constant-volume and cyclic-shear loading conditions was conducted for undisturbed and unsaturated samples of pumice fall deposit to evaluate shear strength properties and seismic behaviors. Based on the slope stability analysis followed by the soil runout analysis at Takanodai, the pumice fall deposit layer shows a large horizontal displacement. While pumice fall deposit layer has enough stability under a normal condition, the strength reduction induced by the soil particle crushing is considered to be one of the factors caused a long runout landslide at the above site.