单轴压缩土样剪切带内、外主应变轴偏转角统计分析

Statistical analyses of principal strain axis rotational angles in shear bands and outside for clay specimens in uniaxial compression

根据单轴压缩低液限黏土试样纵向应变较高时清晰剪切带内最大剪切应变(由数字图像相关方法获得)高值点位置布置曲折测线,并在曲折测线两侧布置平直测线,对测线上主应变轴偏转角和最大剪切应变进行了统计分析.研究发现,随着纵向应变的增加,对于根据左旋剪切带布置的曲折测线,主应变轴偏转角正值(逆时针偏转)所占比例呈增加趋势或保持不变,对于根据右旋剪切带布置的曲折测线,主应变轴偏转角正值所占比例呈减小趋势;对于根据左旋剪切带布置的平直测线,主应变轴偏转角正值所占比例呈减小趋势,对于根据右旋剪切带布置的平直测线,主应变轴偏转角正值所占比例呈增加趋势;当微裂纹刚出现时,右旋剪切带内主应变轴偏转角以负值(顺时针偏转)为主,而左旋剪切带内主应变轴偏转角以正值为主,剪切带两侧附近大部分区域主应变轴偏转方向与剪切带内的相反;剪切带内主应变轴偏转角的高峰和低谷通常与最大剪切应变的高峰或低谷对应或相邻;当较清晰剪切带出现后,剪切带外主应变轴正在偏转方向与剪切带内主应变轴偏转总量方向通常相反.

Statistical analyses of maximum shear strains obtained by use of the digital image correlation method and principal strain axis rotational angles are conducted for low liquid limit clay specimens in uniaxial compression. Some curved monitored lines are arranged according to higher maximum shear strain positions in apparent shear bands at higher longitudinal strains, and some straight monitored lines are arranged at both sides of curved monitored lines. The following results are found. With an increase of the longitudinal strain, the percentage of positive values(anticlockwise rotation) of principal strain axis rotational angles shows an increasing or invariable trend for straight monitored lines arranged by sinistral shear bands, while it shows a decreasing trend for curved monitored lines arranged by dextral shear bands. The percentage of positive values of principal strain axis rotational angles shows a decreasing trend for straight monitored lines arranged by sinistral shear bands, while it shows an increasing trend for curved monitored lines arranged by dextral shear bands. When microcracks just occur, most of principal strain axis rotational angles for dextral shear bands are negative(clockwise rotation), most of principal strain axis rotational angles for sinistral shear bands are positive, and principal strain axis rotational angles near shear bands are usually opposite to those in shear bands. Positions of higher and lower values of principal strain axis rotational angles are consistent with or adjacent to those of higher or lower of maximum shear strains. Once an apparent shear band occurs, current rotational directions of principal strain axes outside the shear band are usually opposite to total rotational directions of principal strain axes in the shear band.