【作者】 王莉莉；

【导师】 邵龙潭；

【作者基本信息】 大连理工大学 ， 岩土与环境力学， 2009， 硕士

【摘要】 本文将大连理工大学环境土力学研究室自行研制开发的三轴试验土样变形的数字图像测量系统应用于土工三轴试验,克服传统接触式变形测量方法的不足,提高了变形测量的精度,为土工三轴试验提供了全新的、更合理有效的变形测量手段。通过对黑色乳胶膜上白色角点的捕捉识别,得到每时每刻的角点信息,从而整理分析局部与整体的强度和变形特性;再利用有限元分散得到全表面的变形场,进而研究剪切带的形成、发展及影响因素等相关问题。以哈达山砂土作为试验土体,充分利用数字图像测量技术的高精度性,研究其强度和变形特性。试验结果表明:(1)围压是影响砂土强度和变形的一个很重要的外部因素,围压越大,达到同一轴向应变值时主应力差值越大。一般情况下,高围压下主应力差和轴向应变曲线上容易出现峰值点,砂土易表现为应变软化型,低围压下应力应变曲线上没有明显的峰值,加载到一定程度后主应力差随轴向应变的变化不大,砂土易表现为应变稳定型。(2)密实度也是影响土强度和变形的一个重要因素,密实度大的砂土其强度相比较大,相同密实度下,中砂较细砂强度大,不易变形。(3)在加载初期,体积应变随时间的关系曲线上都有一小段斜率变小的阶段,然后又逐渐增大,证实了砂土的剪胀(剪缩)性。(4)由于端部约束作用,试样中间四层的轴向应变和径向应变都较之整体变形大,所以整体主应力差较之中间四层主应力差大。以哈达山砂土作为试验土体,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。试验结果表明:(1)哈达山砂土三轴试样出现剪切带的必要条件可能是土样具有较大的相对密度和相对较高的周围压力,相对较高的试样和不饱和状态的试样比较容易出现剪切带。(2)在试验过程中出现剪切带的土体,其应力应变曲线上有明显峰值,剪切带完全形成后,土体强度趋近于残余强度。没有出现剪切带的土体,其应力应变曲线变化趋势很缓慢,没有峰值出现。如鼓胀塑性变形,其应力应变曲线一直变化非常缓慢。(3)试验过程中的剪切速率对剪切带的形成也是一重要影响因素,从试验数据处理的结果看,大的剪切速率加快了剪切破坏的形成。更多还原

【Abstract】 The application of digital image processing technique for local deformation measurement in triaxial test brings a lot of advantages comparing to the traditional measurement method. It improves the accuracy of deformation measurement, and provides a new, more reasonable and effective method in specimen deformation measurement. By capturing and identifying the black rubber membrane of the white corner, get the corner point information of every moment, which analyzed the part and the overall strength and deformation characteristics. Re-use of the finite element dispersion to get full-surface deformation field, to study shear band formation, development and affecting factors and so on.Based on the high precision characteristics of digital image processing technique, using hadashan sand as test specimen, the strength and deformation characteristics are studied. The laboratory test results show that: (1) Confining pressure is a very important external factor that affects the strength and deformation of sands, the higher the confining pressure, the larger is the deviatoric stress when they reach the same strain. In general, it’s easier to observe the peak-point in deviatoric stress and axial strain curve, sand tends to display strain-softening behavior. There is no obvious peak-point in stress-strain curve when the confining pressure is low, when the load reaches a certain high value, there is no obvious difference in stress-strain curve, sand is easy to show strain stability. (2) The density is also a very important factor that affect the strength and deformation of sand, the higher the density, the stronger the strength. Medium sand has a higher shear strength than the fine sand when they have the same density, so the medium sand is difficult to deform. (3) During the initial loading period, there is a small zone where the gradient is initially negative and then become positive in the volume strain-time curve, it is proved that the shear contraction(shear dilatation) of the sand. (4) As a role of end restraint, the middle four pieces compared to the overall specimen, the former have higher axial and radial strain, so deviatoric stress of the overall compared to the middle four pieces is higher.Based on the planar characteristics of digital image processing technique, using hadashan sand as test specimen, the characteristics of triaxial specimen, the stress-strain characteristics, the formation conditions and the influencing factors of shear band were studied. The laboratory test results show that :(1) The necessary condition under which shear band might appear in hadashan sand specimen was the relatively high density, high cell pressure and a relatively low degree of saturation. (2) For the specimen which has shear band during the triaxial test, there is a obvious peak-point in the stress-strain curve, specimen’s strength reaches the residual strength. There is no peak-point in the stress-strain curve and the curve is flat for the specimen without shear band, take the drum deformation for example, there is little change in the stress-strain curve. (3) Shear rate is also a significant influencing factor to the formation of the shear band during the triaxial test; the testing data show that, the rapid shear rate accelerates the formation of the shear band.更多还原