基于全表面测量的三轴土样剪切破坏过程研究

发布时间：2018-02-25 16:42

本文关键词： 全表面数字图像测量三轴试样剪切带应变局部化损伤破坏　出处：《大连理工大学》2017年博士论文　论文类型：学位论文

【摘要】：土体剪切带的形成和土的渐进破坏理论是岩土工程界广泛关注的课题。土体的剪切带是一种典型的应变局部化现象,应变局部化带(剪切带)的产生意味着土体结构发生破损、开始失去稳定性,也标志着土工结构物即将发生失稳与破坏。因此,对土体剪切带问题的研究越来越受到国内外学者的重视。目前,对剪切带问题的研究主要包括理论分析、数值模拟和试验研究三个方面。而基于理论分析和数值模拟的结果大多与试验观测有一定的偏差。对剪切带的变形全过程只有定性的分析,也未给出破坏过程的定量分析标准。其次,现有土体本构模型的建立是将三轴试样视为单元体,而应变局部化现象表明土体的变形是不均匀的,特别是在土体结构产生剪切带之后。因此,在分析具有变形局部化特点的土样时,该类模型则不再适用。本论文主要是围绕这两个问题采用全表面数字图像测量系统对试样的整体变形及局部变形进行实时同步测量分析,为土体剪切带问题的研究提供了有效的手段。论文首先选取标准砂、硅微粉、桂平粘土及高岭土材料进行三轴压缩试验,通过全表面变形数字图像测量系统可得到试样整体和试样表面任意标记点处的应力应变关系曲线及土样全表面的位移场图和应变场图,借助于位移场图和应变场图可以清晰地观察和分析试样的变形情况。我们发现:在试验初始时刻,试样变形比较均匀,试样表面没有明显的局部变形破坏。随着试验的进行,试样出现了变形的不均匀趋势,进而出现局部剪切破坏区域。此后,破坏区域不断地延伸、扩展,最终形成贯穿试样的剪切带。由此,试样的变形分成两种类型:一种是位于剪切带内的土样,变形继续增加、应力保持不变,其受力变形状态类似于滑块的滑动摩擦;另一种是位于剪切带外的土样,在试验后期其变形与受力都保持不变,基本呈现一个近似于零应变增量的状态。此时,试样的变形大多集中在剪切带的内部,主要来源于被剪切带分成两部分的土体之间的滑动。三轴试样的剪切带在何时开始产生、何时完全形成以及其发展变化的规律如何,这个问题一直困扰着土力学界的专家学者。本文中作者根据全表面图像测量技术得到的试样上任意一点处的应变值,定义了两种判别剪切带开始形成及完全形成时刻的方法。第一种是剪切带的应力水平判别方法,即通过实测的试样弹性模量和应变值,得到试样上各标记点的应力。定义应力水平为S=qp/qf,当S=1时,表明试样在该处出现剪切破坏,S=1等值线所包围的区域就是试样的剪切破坏带;第二种是剪切带的应力应变联合判别方法,即将每组试验中土样表面192个标记点中最晚出现轴向应变拐点的时刻作为剪切带完全形成的时刻点;采用应力判断的方法,将土样上各标记点应力值最早达到峰值应力的时刻作为剪切带开始发生的时刻点。应变局部化现象表明,土体的变形是不均匀的,并且在试验的不同阶段试样的变形规律也不尽相同。通过分析土样的局部变形特性及不同阶段的变形机理,把土样的受力变形过程和应力应变曲线分成破坏前阶段、破坏阶段和破坏后阶段。在破坏前阶段,土样各部分变形大体均匀、性质相同,基本满足同一应力应变曲线,土样可以被看作是一个单元体。在破坏阶段,土样从某一点(REV)开始出现破坏并逐渐发展,最后形成贯穿的剪切带,观测到的土样整体的变形是剪切带内和剪切带外土体变形的综合结果。在破坏后阶段,土样的变形源于土体沿着剪切带的滑动,即上下两个斜切体沿着剪切带的滑移,不能再据此计算土样的"应变"。三轴试样从试验初始均匀变形至最后被剪切带完全贯穿直至破坏,其整个变形发展情况反映出了试样结构体的损伤破坏过程。为了分析土样在剪切过程中结构损伤破坏的变化规律,定义了描述土样损伤发育程度的损伤破坏变量W,建立土样的剪切损伤破坏演化方程。采用试样橡皮膜上各标记点的轴向应变的方差来定义剪切带完全贯穿试样之前试样的损伤破坏变量,通过分析损伤破坏变量的规律特性得到试样的损伤状态。在三轴剪切试验过程中,土样的类型、试验围压等都会对损伤演化过程产生影响。剪切损伤破坏分析中,当试样的剪切带完全形成时,认为土样达到完全破损状态,此时W = 1;在试验开始至剪切带完全形成的过程中,W的数值满足从0到1逐渐递增的规律。
[Abstract]:With the soil formation and soil shear failure theory is widely concerned in the field of geotechnical engineering subject. The shear band is a kind of typical strain localization phenomenon, strain localization band (shear zone) which means the soil structure damaged, began to lose stability, also marks the impending loss of soil structure stability and destruction. Therefore, the research on shear band problem more and more attention by scholars. At present, the research on the shear band problems mainly include theoretical analysis, numerical simulation and Experimental Research on three. Theoretical analysis and numerical simulation results based on experimental observation and mostly has a certain deviation of. The whole process is only qualitative shear deformation and failure process are also not quantitative analysis standard. Secondly, the establishment of constitutive model of soil is three existing specimen as a unit, and should become the local The phenomenon shows that the deformation of soil is not uniform, especially after the formation of shear bands in soil structure. Therefore, with the characteristics of soil deformation localization in the analysis, the model is no longer applicable. This thesis mainly adopts full digital image measurement system, the whole surface deformation of the specimen and the local deformation analysis of real time synchronization the measurement on these two issues, provides an effective means for the study of shear band problems. Firstly, the criteria for the selection of sand, silica powder, Guiping clay and kaolin materials were three axial compression test, deformation of digital image measurement system can get the whole sample and the sample surface marker points of stress strain curves and the soil displacement field and strain field of surface figure figure through the whole surface, with the help of the displacement field and strain field map map can clearly observe and analyze the deformation of the sample we sent. Now: in the initial test, the specimen deformation is relatively uniform, no obvious local deformation of specimen surface damage. During the trial, the sample appeared uneven deformation trend, and regional local shearfailure. Since then, failure zone extends continuously, expansion, eventually forming shear through specimen zone. Thus, the sample the deformation is divided into two types: one is located in the shear zone, soil deformation, stress continues to increase, remain unchanged, the stress and deformation state is similar to the slider sliding friction; the other one is located in the soil shear bands, at the end of the experiment, the deformation and stress are unchanged, showing an approximate to zero strain increment state. At this time, the deformation of the specimen are mostly concentrated in the inner shear zone, mainly from sliding between soil is divided into two parts of the shear zone. Three axis specimen shear zone when the beginning of birth Students, when fully formed and the laws of its development and change, the problem has been plagued by experts and scholars of soil mechanics. This paper based on the strain of an arbitrary point samples obtain full surface image measurement technology on the value, defines two kinds of discriminant of shear band formation and formation method. The first time is shear stress level discrimination method, namely through the specimen modulus and strain measured values of stress markers on each specimen. The definition of stress level is S=qp/qf, when S=1, the sample shear failure in the shear failure, surrounded by S=1 contour area is the sample zone the second is; shear zone should be combined with discriminant method of stress and strain, the soil surface of each test 192 marks the latest axial strain inflection point time as the formation of shear band point; the Method of stress judgment, the marks of soil stress on the value of the first peak stress time as the shear band occurs. The strain localization phenomenon, the deformation of soil is not uniform, and the deformation law in different stages of the test are not the same. The deformation mechanism analysis of local deformation characteristics of soil samples and in different stages, the soil samples by the process and the stress-strain curve is divided into stages before the failure of deformation, failure stage and failure stage. After the destruction before the stage, the soil deformation in uniform, similar in nature, basically meet the same stress strain curve, soil can be is regarded as a unit. In the failure stage, soil samples from a point (REV) began to undermine and gradually development, finally formed through the shear zone, the observed soil overall deformation is outside the shear band and the change of soil The comprehensive results form. After the destruction stage, the source of soil sliding deformation in the soil along the shear zone, the upper and lower two bevel along the slip of shear bands, cannot calculate the soil "strain". Three specimen from initial to final test of uniform deformation by shear zones thoroughly destroyed the development of the whole deformation, reflect the failure process of specimen structure damage. In order to analysis of the change of structural damage in the shearing process of soil samples, soil samples is defined to describe the damage degree of the development of the damage variable W, the establishment of soil shear damage and failure evolution equations. Using the variance of axial strain of each marker sample the rubber membrane on the definition of shear band through the sample before sample damage variables, through the analysis of characteristics of damage variables are damage damage state of the sample. The test process in the three axle shear In the type of soil, confining pressure will affect the damage evolution process. The shear damage analysis, when the specimen is in the formation of shear band, that soil completely damaged, at W = 1; in the process of testing to the formation of shear band in W numerical meet from 0 to 1 gradually increasing regularity.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU43

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