Liquefaction resistance of partly saturated sand located immediately beneath groundwater levels

液化发生的可能性通常是通过对完全饱和的土壤标本进行实验室试验来评估的，假设地下水位以下的土层完全饱和。然而，根据原位速度剖面测量，发现由于含有少量气泡，饱和程度降低，因此在地下水位以下的纵波速度低于在远低于地下水位的完全饱和土层中测量的纵波速度。本研究的目的是正确地评价存在于地下水位以下的部分饱和砂土的液化阻力和流动特性。研制了能够测量纵波和横波速度的三轴试验机。研究了b值、饱和比Sr与纵波速度之间的关系，其中在实验室试验中用b值和Sr评价饱和程度，在现场用纵波速度评价饱和程度。此外，通过不排水单调和循环三轴试验，研究了部分饱和砂土的液化阻力和流动特性与纵波和横波速度的关系。

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.