Effect of saturation on liquefaction properties of various volcanic ash coarse-grained soils under unsaturated conditions

Saturated and unsaturated cyclic shear tests were conducted on six types of volcanic ash coarse-grained soils distributed in Japan to determine cyclic shear deformation characteristics and liquefaction characteristics with decreasing saturation. The test results showed that the liquefaction resistance increased with decreasing saturation except for the bora, which is a pyroclastic fall deposit. However, the increasing tendency is insensitive in relation to the medium density Toyoura sand, and liquefaction resistance due to reduced saturation does not increase as much as in the medium density Toyoura sand. Shikotsu pumice flow deposit and Shirasu, which is the pyroclastic flow deposits, the tendency of increasing liquefaction resistance in the 80% to 70% saturation range was sensitive to the pyroclastic fall deposits in the pyroclastic flow deposits, and the increase in liquefaction resistance with decreasing saturation was greater in the pyroclastic flow deposits with higher initial fine-grained content than in the falling pyroclastic deposits. Bora showed little change in liquefaction resistance with decreasing saturation and no clear increasing tendency.