Laboratory shear tests on rate-dependent nature of liquefied sand undergoing large deformation

present study has been attempting to verify that liquefied sand has a rate-dependent nature，作为直接measuring the viscosity coefficient. This aim has been important becauseliquefaction-induced deformation of sandy ground is urgently needed for safety oflifeline facilities as well as river dikes and harbor structures. Model tests have been conducted bymany research institutes for this goal and several values of viscosity已被监测。shortcoming of this way of study is model tests cannot directly measure the stress and strainof liquefied sand，and the values of viscosity as back calculated from test results cannot be examined.With this viewpoint,present study initiated laboratory shear tests for measuring the viscosity. In the first stage，a hollow cylindrical torsion shear device was employed with little success. The课learned fromit are；A liquefied specimen forms A water film at its top and consequently torsion shear becomesdifficult . moreover,true state of liquefaction cannot be attained because of dilatancy which under rainedconditions increases the effective stress and makes sand stiff. Accordinglythe second stage of study employed triaxial compression tests in which a possible water film at thespecimen top did not affect loading of compressional force. Moreover，这是在一个drained manner while controlling artificially the pore pressure测试high and effective stress low.The major findings from the study are；- viscosity coefficient of liquefied sand is in The range of 500 to 4000 kPa.- A dry specimenexhibits a smaller viscosity关于50%的viscosity in a water saturated specimen is generated by pore water；可能性vortex in pore water among moving sand grains plays an important role.Alluvial sand withfines has a smaller viscosity than uniformly graded sand。

The present study has been attempting to verify that liquefied sand has a rate-dependent nature, as well as directly measuring the viscosity coefficient. This aim has been important because prediction of liquefaction-induced deformation of sandy ground is urgently needed for safety of lifeline facilities as well as river dikes and harbor structures. Model tests have been conducted by many research institutes for this goal and several values of viscosity have been obtained. The shortcoming of this way of study is that model tests cannot directly measure the stress and strain of liquefied sand, and the values of viscosity as back calculated from test results cannot be examined.With this view point, the present study initiated laboratory shear tests for measuring the viscosity. In the first stage, a hollow cylindrical torsion shear device was employed with little success. The lesson learned from it are ;- A liquefied specimen forms a water film at its top and consequently torsion shear becomes difficult.- Moreover, the true state of liquefaction cannot be attained because of dilatancy which under undrained conditions increases the effective stress and makes sand stiff. Accordingly, the second stage of study employed triaxial compression tests in which a possible water film at the specimen ユs top did not affect loading of compressional force. Moreover, it was decided to run tests in a drained manner while controlling artificially the pore pressure high and effective stress low.The major findings from the study are ;- The viscosity coefficient of liquefied sand is in the range of 500 to 4000 kPa.- A dry specimen exhibits a smaller viscosity, suggesting that about 50% of viscosity in a water saturated specimen is generated by pore water ;probably vortex in pore water among moving sand grains plays an important role.Alluvial sand with fines has a smaller viscosity than uniformly graded sand.