不同于常规土体单元试验中恒定围压的应力路径，进行了减围压（卸载）应力路径下丰浦砂的平面应变压缩试验，研究了初始围压和初始相对密度对砂土的剪切强度和剪切带特性的影响。结合二维数字图像（DIC）相关方法，分析剪切带的形成过程，对剪切带的厚度和倾角及其影响因素进行定量地分析。研究结果表明，剪切带形成于峰值剪切强度之前；对于密实丰浦砂试样，随着围压的增加，其剪切强度(最大有效主应力比)减小且峰值强度出现越晚，剪切带厚度减小而剪切带倾角变化不大；丰浦砂试样的相对密度越高，剪切强度越大且峰值强度出现越早，剪切带厚度越小而剪切带倾角越高。此外，基于峰值内摩擦角的Coulomb公式可以较好地预测平面应变试验条件下丰浦砂的最大剪切带倾角。

Different from the typical stress path often used in triaxial or plane strain test, a stress path with decreasing confining pressure was applied to plane strain compression test on Toyoura sand. Influence of initial consolidation pressure and initial relative density of sand specimen was investigated. By using the 2D digital image correlation(DIC) method, shear band formation process was analyzed. Shear band thickness and inclination angle, as well as their influencing factors were analyzed quantitatively. Study results show that shear band in the Toyoura sand appeared before the peak shear strength. For dense Toyoura sand, with increasing confining pressure, shear strength(principal stress ratio) decreases and its peak value appears later; shear band thickness is smaller but shear band inclination angle change is not obvious. With increasing relative density, peak shear strength increases and appears at an earlier strain; shear band thickness becomes smaller while shear band inclination angle becomes higher. Moreover, the Coulomb’s equation based on the peak internal friction angle can relatively accurately predict the maximum shear band inclination angle of Toyoura sand under plane strain compression.