三轴试验土样剪切破坏过程的判别

本文在土工三轴试验中应用土样全表面变形数字图像测量系统,通过跟踪包裹土样的橡皮膜表面的标记点,得到加载过程中其全表面的变形和应变分布。根据土样表面的应变分布和实测的应力应变关系曲线,可以得到每一时刻土样表面的应力分布。于是,土样表面剪切破坏开始出现的时刻和剪切破坏带贯穿的时刻可分别依据应变和应力判定。依据应变,将橡皮膜上各点的轴向应变的拐点最晚出现的时刻作为剪切带完全贯穿的时刻;依据应力,将全部点中某一个或几个点最早达到峰值应力的时刻作为剪切带开始出现的时刻;土样各点相继达到应力峰值的过程就是剪切破坏的过程。以剪切破坏的起始点和剪切带贯穿的点为分界,土样剪切破坏过程可以划分成三个阶段:破坏前阶段、破坏阶段和破坏后阶段,在不同阶段土样具有不同的变形特点和变形机理。

Discriminant Method of Shear Failure Process of Soil Specimen in Triaxial Test

A digital image measuring system was adopted to measure the whole surface deformation of soil specimen in triaxial experiment. The deformation and strain distribution on the whole soil specimen surface during loading process were obtained by tracking the marks on specimen's coating rubber film. According to strain distribution on specimen surface and the measured stress-strain curve, the stress distribution on specimen surface can be obtained at every moment. So, the shear band onset moment and shear band penetration moment can be judged based on strain and stress respectively. Firstly, according to the strain, taking the latest moment corresponding to axial strain turning point of points on rubber film as the moment of shear band complete penetration, secondly, according to the stress, taking the earliest moment corresponding to peak stress of one or several points in all points as the onset moment of shear band, the process that the points on specimen reach the peak stress one after another is exactly the process of shear failure. Thus, taking the onset moment of shear band and the moment of shear band complete penetration as cut-off points, the shear failure process of soil specimen can be divided into three stages: the pre-failure stage, the in-failure stage and the post-failure stage, respectively. On different stages, the deformation characteristics and deformation mechanism of soil specimen are different.