单轴压缩湿砂土试样主应变轴偏转规律试验研究

Experimental studies of rotation angles of principal strain axes for wet sandy soil specimens under uniaxial compression

利用自主开发的基于粒子群优化的数字图像相关方法,获得了单轴压缩湿砂土试样观测平面内主应变轴偏转角的时空分布规律。采用双三次样条插值方法,获取了任意位置的主应变轴偏转角,分析了土样将来出现剪切带位置、剪切带的中心及其尖端附近和剪切带外的主应变轴偏转角随纵向应变的演变规律。研究发现,随着纵向应变的增加,在土样观测平面内,主应变轴偏转角的范围由分散逐渐变得稳定,大部分区域最终分布在-10°~10°之间。当出现较清晰的剪切带以后（硬化阶段后期）,剪切带内不同位置处主应变轴偏转角基本趋于恒定或稍有下降,大致稳定在-5°~5°之间,这与剪切带外的点的主应变轴偏转角均处于发展之中不同;而在剪切带尖端附近的点,主应变轴偏转角随纵向应变的演变规律比较复杂。

Using the self-developed digital image correlation method based on the particle swarm optimization algorithm, the spatiotemporal distributions of rotation angles of principal strain axes for wet sandy soil specimens are investigated under uniaxial compression. Using the bicubic spline interpolation, the rotation angles of principal strain axes at any positions are obtained to study the evolution of the rotation angles of principal strain axes with the longitudinal strains before the occurrence of a shear band, at its center, in the vicinity and at both sides of the band. It is found that with the increase of longitudinal strain, the rotation angles of principal strain axes change from a scattered distribution to a stable one; and at last, its range in most regions is-10°-10°. After the occurrence of an apparent shear band at the late stage of strain-hardening, at the center of the band, the rotation angles of principal strain axes tend to be stable or descend slightly, within a range of-5°-5°, while those at both sides of the band still increase. At tip of the band, the evolution of the rotation angles of principal strain axes is complex.