【作者】 田思磊；

【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】 三轴试验是最常用的土工试验之一,通过测得试样应力和应变的变化来推导土体的本构模型参数。而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。本文的研究基础就是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,主要研究了含有石英砂颗粒体材料的应力应变关系和泊松比特性。通过室内三轴试验方法研究了石英砂颗粒体材料在小应变条件下的应力应变特性。试验结果表明:(1)石英砂颗粒体材料在小应变(轴向应变为1%范围内)条件下的应力-应变关系比较符合理想弹塑性模型。试样的线性段区域很小,线性段所对应的轴向应变也基本在0.3%甚至更小范围内。(2)石英砂颗粒散粒体在极小变形条件下剪切模量很大,随着应变的增加,剪切模量逐渐减小。(3)石英砂颗粒散粒体的轴向变形-体积变形符合加载初期体积剪缩关系。剪缩变形部分很小,不到0.2%,与弹性阶段对应,符合弹性变形规律。另外,通过室内三轴试验方法研究了循环加卸载条件下的石英砂颗粒体材料应力-应变及轴向、径向和体积与时间的关系,试验结果表明:(1)石英砂颗粒体材料在第一级加卸载阶段,即10N～1/4P范围内的的变形属于弹性变形阶段,卸载能恢复的轴向和径向变形很小,试样的整体变形还是表现为卸载体积膨胀,经过5次加卸载循环后试样颗粒排列组合就达到了一个相对平衡状态。(2)石英砂颗粒体材料在第二级加卸载阶段,即1/4N～1/2P范围内的的应力应变曲线逐渐进入非线性阶段,这是由于随轴向荷载增大而产生的试样颗粒间滑移、滚动和错位等变形所致,卸载可恢复的变形轴向,径向和体积变形能恢复的则更少,而且随加卸载过程的进行,每一循环加卸载点之间的变形却有减少的趋势,这说明了颗粒间的变形趋于稳定。(3)石英砂颗粒体材料在第三级加卸载阶段,即1/2～70%P范围内的,颗粒之间的相对滑动、滚动位移变大,并且颗粒破碎程度增大,试样的塑性变形迅速增加,试样变形趋于稳定的时间也变长。同时试样的轴向、径向和体变的变化也减小,试样也逐渐进入稳定状态。(4)试样从初始状态分别直接加载到1/2P和70%P进行单级循环加卸载的轴向、径向、体积变化与时间的关系曲线中可以看到,其关系曲线中的结果与3级加卸载因为加载历史的不同而略有差异,但其关系曲线的变化趋势基本上一致。通过对石英砂颗粒体材料在小应变条件下三轴试验和循环加卸载条件下试验,讨论其泊松比的特性,得到以下结论:(1)石英砂颗粒体材料在小应变条件下轴向应变-径向应变在加载的初期表现出曲线,变形一定阶段后,轴向应变和径向应变显现出线性变化趋势,而且不同围压下曲线变化规律基本保持相同。(2)石英砂颗粒体材料的泊松比在加载初期基本都是在0.1-0.3开始变化,达到0.5时的轴向应变都很小。(3)将循环加卸载过程分成3级阶段分别讨论其泊松比变化情况。加载初始,泊松比从0.2-0.3之间开始,这与常规三轴试验结果基本一致,在达到0.5时对应的轴向应变很小,而后的每一级循环过程中的加卸载中,泊松比变化整体上很稳定,表现出卸载条件下,泊松比有略微增加变化,加载条件下,泊松比有略微减小的变化,而且基本上都维持在正常加载到每一级应力峰值点时的泊松比值。更多还原

【Abstract】 Tri-axial test is one of the most common soil tests,which determines the soil constitute model parameters through the measurement of stress-strain relationship.The application of digital image processing technique for local deformation measurement in tri-axial 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 taking the advantage of digital image processing technique,the stress-strain characteristics and Poisson’s ratio of Quartz sand are studied.The Quartz sand is studied through the tri-axial compression tests.Laboratory tri-axial tests are carried out in order to understand the stress-strain relationship in the small strain condition.The laboratory test results show that:(1) the stress-strain relationship of Quartz sand in the a little strain condition is measured as elastoplastic model.The linear part is very small and the axial strain is about 0.3%;(2) the shear modulus of the Quartz sand is very large in the small strain and the shear modulus is getting smaller with the increase of the strain;(3) the axial strain-volume strain relationship of Quartz sand is measured shrinked and the relationship is measured as elastic variation.The Quartz sand is studied through the tri-axial cyclic loading experiment.We get the relation of the axial,radial and volume strain-time.The test results show that:(1)In the first cyclic loading part,the variation is the elastic,the axial and radial variation is rather small and the volume will shrink in unloading.After 5 times cycle,the Quartz sand arrives the balance condition.(2) In the second cyclic loading part,the stress-strain relationship arrives the non-linear part,which is due to the slippage,rotation and crushing.the axial and radial variation is much smaller with the cycle experiment.that is because the variation of the Quartz sand arrives at the stable state.(3) In the third cyclic loading part,the slippage, rotation and crushing is vigorous,the plastic variation is increasing,the time of the stable state will be longer.(4) In the second cyclic loading part without the first part and the third cyclic loading part without the previous two parts experiments,we get the nearly same the variety law though they are different from the loading history.The Poisson’s ratio is studied through the tri-axial compression tests and tri-axial cyclic loading experiment.The test results show that:(1) The relationship of the axial-radial strain is curve at the loading beginning and is the linear variation after some time.And the variety law is the same in the different cell pressure.(2)The Poisson’s ratio is between 0.3 to 0.5 at the loading beginning.The axial strain is small when the Poisson’s ratio arrives at 0.5.(3) For studying the Poisson’s ratio,we divide the cyclic loading experiment into 3 periods.The Poisson’s ratio is between 0.2 to 0.3 at the loading beginning,as the same as the tri-axial compression test.When the Poisson’s ratio arrives at 0.5,the axial strain is very small.The Poisson’s ratio of every cycle period keeps stable and the Poisson’s ratio value is nearly the same as the value when the stress arrives at the every stress peak.Besides the Poisson’s ratio number increase a little in the unloading parts and decrease a little in the loading part.更多还原