【作者】 孙益振；

【导师】 邵龙潭；

【作者基本信息】 大连理工大学 ， 岩土工程， 2006， 博士

【摘要】 局部变形数字图像测量技术在三轴试样变形测量中的应用,克服了传统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。本文对局部变形测量条件下土体的变形特性进行了试验研究。 分析了不同因素造成的测量误差,提出了相应的消除或减小误差的方法。在测量系统的正常使用条件下,系统的精度可以达到理论精度,满足试样变形高精度测量的要求。 利用三轴试样变形图像测量系统开展了膜嵌入问题研究。选取Duncan-Chang模型、剑桥模型与南水模型,并以Duncan-Chang模型为主对基于局部变形测量结果的土体应力应变特性进行了分析。通过对模型参数确定方法的研究,分析了局部变形与整体测量方法得出的参数产生差异的原因及对计算结果的影响。由于测量方式和测量部位的不同,Duncan-Chang模型中反映初始弹性模量与初始体积模量的参数K、n和K_b、m的差别很大,特别是K和K_b值;南水模型中由局部变形测量结果得出的R_d、c_d、d与传统整体变形计算的结果存在很大差异;剑桥模型中参数λ、κ也因体积测量结果及变化规律的不同而有成倍的差异。由存在差异的参数计算土体变形的结果也不同。 土体泊松比是反映土体侧向变形的重要参数。通过对泊松比试验结果进行的分析,得出了泊松比的变化规律:轴向应变～径向应变关系曲线的变化规律在各围压条件下仍保持基本相同,切线泊松比在加载初期从0.2～0.3开始变化,达到0.5时的径向变形很小。图像测量局部变形的切线泊松比变化比传统测量整体变形的快,其值也比传统测量整体变形的结果大。随主应力比的增加,切线泊松比随之增加,当土体主应力比达到一定范围后,切线泊松比的值大于0.5,建立泊松比与主应力比之间的关系更符合泊松比取值规律。 分析了砂性材料三轴循环加卸载试验结果,由于颗粒骨架的结构性,加载达到一定荷载后,只要试样体积出现膨胀,卸载就会出现体缩。随着密度、加载范围的增大,卸载体缩现象越明显,卸载体缩现象减退所需要的加卸载循环次数越多。多次加卸载循环后,颗粒的滑移、滚动和破碎等结构性变形最终将完全消除。更多还原

【Abstract】 The application of digital image processing technique for local deformation measurement in triaxial test leads to much advantages comparing to traditional measuring method. It improves the accuracy of deformation measurement, and provides a new, more reasonable and effective method in specimen deformation measurement. By using the digital image processing technique, stress-stain characteristics of soils are studied based on local deformation measurement of soil specimen.Firstly, the thesis analyzes the errors caused by different factors and proposes corresponding methods to eliminate or lessen the errors. Some items for minimizing measurement errors and noticed testing conditions are listed. The precision of digital image processing technique can reach the theoretic precision and satisfy high precision requirement of specimen deformation measurement under steady condition.Secondly, with the help of local deformation measurement in triaxial deformation test, the author studies the membrane penetration of triaxial specimen, and discusses the characteristics of soil stress-stain property in local deformation measurement using Duncan-Chang model along with Cam-clay model and Nanshui model. By studying on the determination method of model parameters, the thesis compares the parameters of the two methods, and discusses the influence on the calculation results. Because of the difference of measurement methods and measurement area, the parameters are different from each other between local deformation and whole deformation measurement of the three models. In Duncan-Chang model, the difference between K, n and K_b , m is notable, particularly K and K_b. In the Nanshui model, there are great differences among R_d, c_d and d. Similarly, there are times of difference between’s parameters λ and κ in Cam-clay model. The calculation results based on these inaccurate parameters are also inaccurate.Thirdly, the soil’s Poisson’s ratio is an important parameter for transverse deformation. The law of Poisson’s ratio in this study is obtained from the experimental results. The axial strain-radial strain variation trend is similar under different confining pressure. The tangent Poisson’s ratio changes from 0.2 to 0.3 at initial loading, and reaches 0.5 at very small strain. The tangent Poisson’s ratio of local deformation changes faster than that of traditional whole deformation measurement and the value of the former is larger than thatof the latter. The soil tangent Poisson’s ratio increases as the principal stress ratio increases. When the principal stress ratio of the soil reaches a certain value, the tangent Poisson’s ratio will be larger than 0.5. It is reasonable to establish the relationship between the Poisson’s ratio and principal stress ratio.Finally, the thesis analyzes the results of triaxial cyclic loading experiment of sandy soil. Due to the attributes of soil’s particle-framework, if loading arrives at a certain extent, the volume will shrink in unloading as long as the specimen expands in loading. With the increasing of density and the load scope, the phenomena of expanding in loading and contraction in unloading become more obvious, and recovering of the contraction of volume need more times of cyclic loading. After several times of cyclic loading, the structural deformation of particles, such as slippage, rotation and crushing, will fade away eventually, and the structure deformation will arrive at a stable state.更多还原