Dynamic Shear Characteristics of Anisotropic Calcareous Sand Under Cyclic Rotation of Principal Stress Axis

In order to study the dynamic shear characteristics of anisotropic calcareous sand under the cyclic rotation of principal stress axis, a series of undrained tests on the cyclic rotation of principal stress axis under the anisotropic consolidation mode were carried out by GDS hollow cylinder torsional shear apparatus. It was found that the anisotropic consolidation mode aggravated the anisotropy in the microstructure of calcareous sand samples and made the generalized shear strain develop from "stable type" to "destructive type" under the cyclic rotation of principal stress axis. For the "stable type" tests, each strain component has a linear relation with the logarithm of the vibration times, thus the empirical formula of the axial strain ε_z and vibration times N of the "stable type" calcareous sand is obtained. With the increase of vibration times, the "destructive type" calcareous sand softens, and the dynamic shear modulus rapidly decreases after 10 vibration times. The softening index R_N is introduced to reflect the softening degree, and the empirical formula for the calculation of softening index R_N and vibration times N is obtained.