A study on liquefaction of volcanic soils including a sedimentation of gravely debris avalanche

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Liquefaction histories and strengths of several volcanic soils were studied. History of liquefaction at volcanic soils during past earthquakes in Japan was studied at first, by collecting reconnaissance reports and geological maps. It was demonstrated that liquefaction has been induced in the ground where volcanic ash, pumice and gravely debris avalanche were deposited. Existing boring data collected at the liquefied sites showed that liquefaction has occurred even though in gravely sand. Detailed soil investigation by borings, Swedish soundings and undisturbed samplings were carried out in Ebino City where liqufaction occurred during the Ebino earthquake at secondary sedimented pumice grounds. Undrain cyclic triaxial tests on undisturbed samples taken at several sites showed that liquefaction strength of secondary sedimented pumice is very low. Based on these studies, liquefiable areas where volcanic soils are sedimented during future earthquakes were pointed out.