Anisotropic deformation characteristics of geomaterials in a wide strain range

本研究新开发了一种由带有自动控制和测量系统的三轴室以及剪切波速度测量单元组成的三轴试验装置，用于小应变水平的测量。首先对系统的稳定性和误差进行了评价。通过小循环加载和剪切波剪切波速测量，对丰浦砂在小应变水平下的刚度和各向异性进行了三轴试验。与空心圆柱扭转剪切试验的结果进行了比较，结果表明，如果采用内部测量以避免层间误差，LDT和LVDT的轴向应变值具有相似的精度。体积变化测量中的误差不仅应针对样品一侧的膜渗透进行校正，还应针对其他系统的顺应性进行校正。并对润滑层及膜与终板间的间隙进行了校正。在该测试系列中，在顶盖和底座处均使用了放大的板用于润滑，并且膜不能完美地配合在试样和板的拐角处。体积变化测量的误差与有效围压的对数成线性关系。通过对小应变水平下的小应变刚度进行适当的修正，可以在10 μ s的小应变水平下精确地确定小应变刚度<-5>。通过小循环加载和剪切波剪切波速测量的三轴试验，测定了丰浦砂在小应变水平下的刚度和各向异性。初步试验结果，并与空心圆柱扭剪试验结果进行了比较。讨论了小应变刚度的应力状态依赖性。

In this study, a triaxial test apparatus which is composed of a triaxial cell with automated control and measurement system together with measurement units for shear wave velocities is newly developed for the measurements at small strain level. Stability and errors of the system were first evaluated. Stiffness and anisotropy of Toyoura sand at small strain level were measured by performing triaxial tests with small cyclic loading and shear wave shear wave velocity measurement. The results were compared with the results obtained by hollow cylindrical torsion shear tests.If internal measurements were made to avoid bedding error, both LDT and LVDT gave the similarly accurate axial strain values. Errors in volume change measurements should be corrected not only for membrane penetration on the side of the specimen but also for other system compliance. Corrections were also wade for the bedding error at lubrication layer and the gaps between the membrane and endplates. In this test series, enlarged plates were used both at a top cap and a pedestal for lubrication, and the membrane could not be perfectly fit at the corner of the specimen and the plate. Errors in volume change measurements were found to change linearly with the logarithm of the effective confining pressure. It was checked that the small strain stiffness could be determined precisely at a very small strain level of 10^<-5>, if the corrections were made properly.Stiffness and anisotropy of Toyoura sand at small strain level were measured by performing triaxial tests with small cyclic loading and shear wave shear wave velocity measurement. Preliminary test results are presented and compared with the results obtained by hollow cylindrical torsion shear tests. Stress state dependency of small-strain stiffness is discussed.