【作者】 董建军；

【导师】 邵龙潭；

【作者基本信息】 大连理工大学 ， 岩土工程， 2008， 博士

【摘要】 基于亚像素角点检测的数字图像测量方法在三轴试验试样变形测量中的应用，为三轴试验试样变形测量提供了一项新方法，该方法通过捕捉跟踪角点的位移对试样变形进行测量，测量结果能够达到较高的亚像素精度（0.02像素），精度分析结果表明应变测量精度可以达到10^-4数量级。应用该方法能够更加准确地测量饱和土和非饱和土三轴试验试样的局部变形，进而深入研究土在三轴应力状态下的应力-应变特性。同时，还可以利用其独特的测量机理，获取相当于将试样表面离散化的变形试验数据，计算出三轴试样的表面应变场对三轴试样的变形性质进行研究。在控制吸力条件下的非饱和压实土三轴试验中应用基于亚像素角点检测的数字图像测量方法，使非饱和压实土三轴试验试样的局部变形测量更加简便，同时克服了接触式传感器会对试样产生径向约束、测量截面少等不足，提高了局部变形测量的精度。由于受到端部约束的影响，测量非饱和压实土试样整体变形的试验结果相对真实情况而言强度被提高，变形能力被降低，由此获得的试验数据不能够真实地反映非饱和土的强度和变形性质。通过比较控制吸力条件下非饱和压实土三轴试验中试样整体与试样中部1／3区域的试验结果，证明测量试样中部1／3区域受端部约束的影响较小，其试验结果更能代表非饱和土的基本受力变形特性，对于研究非饱和土的应力-应变关系可以提供更为可靠的试验数据。采用双应力状态变量强度理论系统分析了试样的抗剪强度，结果表明端部约束对抗剪强度公式的参数取值有较大影响。应用非饱和土Alonso弹塑性模型研究探讨了模型参数取值对非饱和土数值计算结果的影响，使用包含端部约束影响的试样整体变形确定的模型参数进行有限元数值计算将产生误差，同时也高估了非饱和土体的强度。在常吸力的各向等压压缩试验中，试样整体与试样中部1／3区域的变形测量结果趋势一致，同一平均净应力下前者变形小于后者；前者的屈服应力值大于后者，二者的屈服应力都是随着吸力的增加而增大。由试样整体与试样中部1／3区域变形确定的LC屈服曲线模型参数差别较大，试验值和模型计算的p—s平面LC屈服曲线的形式也存在差别，前者的弹性区域明显大于后者。针对Alonso模型中LC屈服轨迹方程中存在的计算结果与试验结果误差较大以及存在不具有普遍意义的假设的问题，基于局部变形试验结果深入研究了LC屈服轨迹方程的合理形式。在一系列常吸力的非饱和压实土三轴剪切试验中，应用数字图像测量方法测量试样中部1／3区域的强度及变形的试验结果表明：吸力对非饱和土抗剪强度的提高有重要影响，抗剪强度随着吸力的增加而增加。基于局部变形测量的常吸力非饱和压实土三轴剪切试验结果，全面描述了非饱和土p—g—s三维应力空间中临界状态面的合理形态：在p—q平面，临界状态线斜率M是与吸力无关的物理量；临界状态面与LC屈服面交线在三维应力空间中是一条存在极值的曲线；该交线在p—s平面的投影曲线在三轴压缩应力状态下应位于第一象限；该交线在q—s平面的投影曲线应存在渐近线；反映凝聚力与吸力关系的函数曲线也应存在渐近线。修正了Alonso模型中临界状态线的表达式，验证了其合理性。依据局部变形试验结果绘制的塑性体应变等值面形状为水滴形，并针对非饱和土Alonso弹塑性模型的不足，将水滴形屈服面扩展到非饱和土中，提出了非饱和土水滴形屈服面函数，采用相关联的流动法则，应用合理的LC屈服轨迹方程和临界状态线的修正表达式，结合对偶应力硬化理论改进了模型，改进模型的计算结果与原模型及试验结果的对比表明，改进模型能够较好地对控制吸力条件下的非饱和土三轴压缩试验进行模拟，其结果与试验结果吻合得较好，优于原模型，进而验证了改进模型是一种合理的形式。更多还原

【Abstract】 Digital image measurement method, which is based on sub-pixel corner detection, is a new technique of triaxial specimen deformation measurement. This technique measures the specimen deformation through the tracking of corner detection displacement, and the result precision can be up to sub-pixel level (0.02 pixel), and the strain measurement precision can up to 10E-4. This new technique can measure the triaxial specimen deformation of both saturated and unsaturated soil more exactly, and can deeply analyze the soil stress-strain property under triaxial stress state. Due to the peculiar measurement mechanism, this technique obtains the deformation test data that discretize the specimen surface, which can be used to calculate the surface deformation field of the test specimen, and then analyze the surface deformation property.The application of sub-pixel corner detection measurement based digital image measurement technique in unsaturated and compacted soil triaxial test under the condition of suction control, makes it convenient to measure the local deformation of the soil specimen, overcomes such shortcomings as radial constraint caused by contact sensor and small measurement section, and improves the precision of local measurement. Because of the influence of end restraint, the integral measurement of unsaturated and compacted soil specimen overrates the specimen strength and underrates the deformation compared to the real situation; hence the test data cannot stand for the real strength and deformation property of unsaturated and compacted soil. The comparison of test result of the overall specimen and the middle 1/3 part of unsaturated and compacted soil specimen under suction control, reflects that end restraint has little influence on the middle 1/3 part, and the test result of this part can stand for the principal deformation property of unsaturated soil, and provides credible test data for the research of unsaturated soil stress strain relationship. The end restraint has great influence on parameter of the shear resistant strength formula, when using two stress state variable strength theory systems to analyze the shear resistant strength. This paper uses unsaturated soil Alonso elasto-plastic model to analyze the influence of model parameter value on numerical calculation. And the result shows that Finite Element numerical calculation which adopts the specimen integral deformation model parameter will generate errors, and overestimates unsaturated soil strength. Under the condition of isotropic compression condition with suction control, the measurement result of the integral specimen and the middle 1/3 part is consistent, and the deformation of the former is less than that of the latter under the critical net stress; the yield stress of the former is greater than that of the latter, and they both increases with the suction increase. But there is obvious difference between LC yield curve model parameters that are obtained from the integral specimen and the middle 1/3 part. And the LC yield curve formats in p - s plane in also different between experiment and model calculation, and the elastic zone of the former is greater than that of the latter. Due to this great error of Alonso model LC yield equation between calculation and experiment, and the uncommon assumption, the reasonable LC yield locus equation is analyzed based on the result of local deformation in this paper.In the unsaturated and compacted soil triaxial shear test, the strength and deformation measurement results of the specimen middle 1/3 part show that the suction greatly affects unsaturated soil strength, which increases with the increase of the suction. The unsaturated and compacted soil triaxial test result under constant suction describes the unsaturated soil critical state surface in p-q-s three dimensional space: in p - q plane, the slope M of critical state line is independent of suction; the cross line of LC yield surface and critical state surface is a curve with extremum in three dimensional stress space, and its projection in p-s plane is located in quadrant 1 in triaxial compression state; its projection in q-s plane has asymptote, and there should also be asymptote in respect of the curve that stands for the function relationship between cohesive and suction. This paper improves the expression format of the critical state line in Alonso model, and verifies its rationality.According to the drip type plastic volume strain isoline obtained by local deformation test result, and due to the defect of unsaturated soil elsato-plastic Alonso model, the drip type yield surface is expanded to unsaturated soil. This paper proposes unsaturated soil drip type surface function, adopts associated flow rule and reasonable LC yield lotus equation and critical state line expression, and improves the model with dual stress hardening principle. The comparison of the calculation result of the improved model and the original model shows that the improved model can better simulate the unsaturated soil triaxial compression test under suction controlled, and the result is better than that of the original model, which further demonstrates that improved model is more reasonable.更多还原