本文關鍵詞： 全表面數(shù)字圖像測量 三軸試樣 剪切帶 應變局部化 損傷破壞　出處：《大連理工大學》2017年博士論文　論文類型：學位論文

【摘要】：土體剪切帶的形成和土的漸進破壞理論是巖土工程界廣泛關注的課題。土體的剪切帶是一種典型的應變局部化現(xiàn)象,應變局部化帶(剪切帶)的產(chǎn)生意味著土體結構發(fā)生破損、開始失去穩(wěn)定性,也標志著土工結構物即將發(fā)生失穩(wěn)與破壞。因此,對土體剪切帶問題的研究越來越受到國內外學者的重視。目前,對剪切帶問題的研究主要包括理論分析、數(shù)值模擬和試驗研究三個方面。而基于理論分析和數(shù)值模擬的結果大多與試驗觀測有一定的偏差。對剪切帶的變形全過程只有定性的分析,也未給出破壞過程的定量分析標準。其次,現(xiàn)有土體本構模型的建立是將三軸試樣視為單元體,而應變局部化現(xiàn)象表明土體的變形是不均勻的,特別是在土體結構產(chǎn)生剪切帶之后。因此,在分析具有變形局部化特點的土樣時,該類模型則不再適用。本論文主要是圍繞這兩個問題采用全表面數(shù)字圖像測量系統(tǒng)對試樣的整體變形及局部變形進行實時同步測量分析,為土體剪切帶問題的研究提供了有效的手段。論文首先選取標準砂、硅微粉、桂平粘土及高嶺土材料進行三軸壓縮試驗,通過全表面變形數(shù)字圖像測量系統(tǒng)可得到試樣整體和試樣表面任意標記點處的應力應變關系曲線及土樣全表面的位移場圖和應變場圖,借助于位移場圖和應變場圖可以清晰地觀察和分析試樣的變形情況。我們發(fā)現(xiàn):在試驗初始時刻,試樣變形比較均勻,試樣表面沒有明顯的局部變形破壞。隨著試驗的進行,試樣出現(xiàn)了變形的不均勻趨勢,進而出現(xiàn)局部剪切破壞區(qū)域。此后,破壞區(qū)域不斷地延伸、擴展,最終形成貫穿試樣的剪切帶。由此,試樣的變形分成兩種類型:一種是位于剪切帶內的土樣,變形繼續(xù)增加、應力保持不變,其受力變形狀態(tài)類似于滑塊的滑動摩擦;另一種是位于剪切帶外的土樣,在試驗后期其變形與受力都保持不變,基本呈現(xiàn)一個近似于零應變增量的狀態(tài)。此時,試樣的變形大多集中在剪切帶的內部,主要來源于被剪切帶分成兩部分的土體之間的滑動。三軸試樣的剪切帶在何時開始產(chǎn)生、何時完全形成以及其發(fā)展變化的規(guī)律如何,這個問題一直困擾著土力學界的專家學者。本文中作者根據(jù)全表面圖像測量技術得到的試樣上任意一點處的應變值,定義了兩種判別剪切帶開始形成及完全形成時刻的方法。第一種是剪切帶的應力水平判別方法,即通過實測的試樣彈性模量和應變值,得到試樣上各標記點的應力。定義應力水平為S=qp/qf,當S=1時,表明試樣在該處出現(xiàn)剪切破壞,S=1等值線所包圍的區(qū)域就是試樣的剪切破壞帶;第二種是剪切帶的應力應變聯(lián)合判別方法,即將每組試驗中土樣表面192個標記點中最晚出現(xiàn)軸向應變拐點的時刻作為剪切帶完全形成的時刻點;采用應力判斷的方法,將土樣上各標記點應力值最早達到峰值應力的時刻作為剪切帶開始發(fā)生的時刻點。應變局部化現(xiàn)象表明,土體的變形是不均勻的,并且在試驗的不同階段試樣的變形規(guī)律也不盡相同。通過分析土樣的局部變形特性及不同階段的變形機理,把土樣的受力變形過程和應力應變曲線分成破壞前階段、破壞階段和破壞后階段。在破壞前階段,土樣各部分變形大體均勻、性質相同,基本滿足同一應力應變曲線,土樣可以被看作是一個單元體。在破壞階段,土樣從某一點(REV)開始出現(xiàn)破壞并逐漸發(fā)展,最后形成貫穿的剪切帶,觀測到的土樣整體的變形是剪切帶內和剪切帶外土體變形的綜合結果。在破壞后階段,土樣的變形源于土體沿著剪切帶的滑動,即上下兩個斜切體沿著剪切帶的滑移,不能再據(jù)此計算土樣的"應變"。三軸試樣從試驗初始均勻變形至最后被剪切帶完全貫穿直至破壞,其整個變形發(fā)展情況反映出了試樣結構體的損傷破壞過程。為了分析土樣在剪切過程中結構損傷破壞的變化規(guī)律,定義了描述土樣損傷發(fā)育程度的損傷破壞變量W,建立土樣的剪切損傷破壞演化方程。采用試樣橡皮膜上各標記點的軸向應變的方差來定義剪切帶完全貫穿試樣之前試樣的損傷破壞變量,通過分析損傷破壞變量的規(guī)律特性得到試樣的損傷狀態(tài)。在三軸剪切試驗過程中,土樣的類型、試驗圍壓等都會對損傷演化過程產(chǎn)生影響。剪切損傷破壞分析中,當試樣的剪切帶完全形成時,認為土樣達到完全破損狀態(tài),此時W = 1;在試驗開始至剪切帶完全形成的過程中,W的數(shù)值滿足從0到1逐漸遞增的規(guī)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.

【學位授予單位】：大連理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TU43

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