砂土应力诱发弹性波速各向异性的试验研究

An experimental study on the stress-induced anisotropic elastic wave velocities of sand

针对砂土弹性模量的各向异性,利用安装在试样上的竖向和水平向弯曲元波速传感器,研究了不同应力状态下丰浦砂试样不同方向的压缩波(P波)和剪切波(S波)波速特征,确定了表征砂土纵观各向异性的弹性刚度矩阵,并探讨了砂土试样中波速各向异性程度随应力状态的演化规律。研究结果表明:在等向应力固结下,丰浦砂试样中不同方向的波速均与围压呈幂函数关系,且存在明显的初始各向异性,试样中沿水平向传播的波速小于沿竖直向传播的波速;在三轴压缩不等向应力固结下,沿竖向传播的弹性波速随竖向应力和水平向应力比值的增加而增加,沿水平向传播的弹性波速随应力比的增加先保持不变后衰减。随着应力比的增加,砂土试样中应力修正后波速的各向异性程度先变化不大后逐渐加剧,这一现象与砂土微观组构的演化有关。

Regarding the anisotropic elastic modulus of sands,the effect of various stress states on the compressional wave(P-wave)and shear wave(S-wave)velocities along multi-directions measured using two pairs of horizontal and vertical bender elements installed on the sample is investigated.A cross-anisotropic stiffness matrix is fully determined based on the measured elastic wave velocities and the evolution of the anisotropy degree of elastic wave velocity with stress ratio is presented.The test results indicate that there exists a power relationship between the elastic wave velocities and the confining pressure in isotropic stress states.Meanwhile,the elastic stiffness of Toyoura sands in the horizontal direction is less than that in the vertical direction,indicating an initial fabric anisotropy.During anisotropic consolidation along a triaxial compression path,the velocities of elastic wave propagating along the vertical direction increase,while those propagating along the horizontal direction first remain constant then decrease as the ratio of vertical stress to horizontal stress increases.Moreover,the anisotropy degree of the stress normalized elastic wave velocity in the sands first keeps almost constant then increases with the increase of the ratio of vertical to horizontal stress,which is attributed to the evolution of soil micro fabric during anisotropic loading.