基于数字图像测量技术的粉煤灰三轴试样剪切带研究

Study on shear band of fly ash triaxial specimen based on digital image processing technique

以粉煤灰作为试验土体,充分利用数字图像测量技术的面场特性,研究三轴试样剪切带的形态、出现剪切带试样的应力应变特性以及剪切带的形成条件和影响因素。试验在改进的高精度三轴仪上进行,为了分析比较,选择不同密度、围压、试样高度和饱和度的三轴试样,共进行了20组固结排水剪切试验。结果表明,粉煤灰三轴试样中出现的剪切带形态各异,没有可以遵循的规律。在试验过程中出现剪切带的土体,其应力应变有明显峰值,剪切带初始形成时刻位于峰值强度之前,剪切带完全形成后,土体强度趋于残余强度。粉煤灰三轴试样出现剪切带的必要条件是土样具有较大的相对密度和相对较小的周围压力,相对较高的试样和饱和状态的试样比较容易出现剪切带。利用数字图像测量技术还可以成功记录三轴试样剪切带发育的全过程,比较容易地确定剪切带开始出现和完全形成的时刻。

Based on the planar characteristics of digital image processing technique, using fly ash as test specimen, the shape of triaxial specimen, the stress-sWain characteristic and formation conditions of shear band were studied. In order to make analysis and comparison, triaxial specimens with different densities, cell pressure and degree of saturation were chosen and 20 groups of consolidated drained triaxial tests were performed on improved high accuracy triaxial instrument. It was shown that there were various shapes of shear band and no certain rule could be followed. During the test, the stress-strain of the existing shear band exhibited obvious peak value, the shear band appeared before the peak value, and the strength tended to be residual strength after the formation of shear band. The necessary condition under which shear band might appear in fly ash specimen was the relatively large density, small cell pressure and relatively high degree of saturation specimen. The digital image processing technique could help to record the whole process of the formation of shear band of triaxial specimen. Then the time of appearence and complete formation of shear band could be determined easily.