Liquefaction resistance of partly saturated sand located immediately beneath groundwater levels

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The possibility of liquefaction occurrence has been conventionally evaluated by performing laboratory tests on fully saturated soil specimens, assuming that the soil layers beneath groundwater levels are fully saturated. However, according to insitu velocity profile measurements, the degree of saturation is found to reduce due to the inclusion of a small amount of air bubbles, and therefore P-wave velocities immediately beneath groundwater levels are lower than those measured in fully saturated soil layers far below the groundwater levels. This study is aimed at properly evaluating the liquefaction resistance and flow characteristics of partly saturated sand existing immediately below the groundwater levels. The triaxial test apparatus capable of measuring P-wave and S-wave velocities is developed. The relationships among the B-value, saturation ratio Sr and P-wave velocities are examined, in which the B-value and Sr are used to evaluate the degree of saturation in laboratory tests, and P-wave velocity is used to evaluate the degree of saturation insitu. Furthermore, in relation to the P-wave and S-wave velocities, the liquefaction resistance and flow characteristics of partly saturated sand are examined by performing undrained monotonic and cyclic triaxial tests.