平面应变条件下原状黄土结构性屈服与破坏力学行为研究

Plain strain loading and unloading problems mostly exist in the loess engineering. Disturbance of excavation, loading and moistening can lead to amounts of engineering disasters such as landslides, subsidence and slip of surround rock. Therefore, it is necessary to study the structural yielding and progressive failure mechanics behavior of loess under the interaction of plane strain compression, shearing and moistening. The research includs: (1) Based on the theory of comprehensive structure potential and breakage mechanics, the plane strain loading and unloading tests of intact, remolded and saturated loess under compression-shearing-moistening action will be carried out. The quantitative parameters of the loess structural evolution process under the conditions of plane strain loading and unloading are proposed and the law of its decay evolution is revealed. (2) By analysis of the loess structural parameters and structural strength, the relationship between the structural parameters and shear yield, strength, deformation of loess under plane strain loading and unloading condition is revealed. (3) Through the isotropic compression test and the plane strain test under different stress paths, the structural evolution method is combined with the elastic-plastic theory and critical state theory. Thus, a constitutive model reflecting structural change of plain strain collapsible loess under the condition of compression-shearing-moistening is formulated. This study could deepen the understanding of loess mechanical property under plain strain condition and then provide a strong theoretical and experimental basis for improving the design and deformation evaluation methods of loess engineering construction under plane strain condition.

针对黄土工程中经常遇到的平面应变加、卸载问题，在扰动、加载和增湿作用下会引起的塌方、沉陷、滑移等工程灾害，研究平面应变压缩、剪切及增湿共同作用下黄土的结构性屈服与渐进破坏力学行为问题，包括：(1)基于综合结构势思想，借鉴破损力学理论，通过压-剪-湿作用下原状、重塑、饱和黄土的平面应变加、卸载试验，提出统一描述平面应变加、卸载条件下黄土结构性演变全过程的定量化参数并揭示其衰减演化规律；(2)以黄土的结构性参数和结构性强度为切入点，揭示平面应变加、卸载条件下黄土的结构性参数与剪切屈服、强度及变形特性的关系；(3)基于等向压缩试验和平面应变试验结果，将结构性演变方式与弹塑性理论和临界状态理论想结合，建立“压-剪-湿”耦合作用下结构性演变的平面应变弹塑性本构模型。研究成果可深化平面应变条件下黄土力学性质的认识，为完善平面应变条件下黄土工程建设的设计和变形评价方法提供有力的理论基础和试验依据。

针对黄土工程中经常遇到的平面应变加、卸载问题，在扰动、加载和增湿作用下会引起的塌方、沉陷、滑移等工程灾害，研究平面应变压缩、剪切及增湿共同作用下黄土的结构性屈服与渐进破坏力学行为问题，包括：(1)针对现有的平面应变试验仪在固结阶段中主应力达不到固结围压以及试验过程中平面应变方向上的主应力难以量测等缺陷，基于西安理工大学真三轴试验系统，对其压力室进行了2次平面应变改造，结果验证了改进的平面应变压力室用于平面应变试验研究的合理性和准确性。(2)通过扰动、加载和浸水充分释放土的结构势，开展Q3原状、重塑和饱和原状黄土的无侧限压缩试验和平面应变剪切试验，依据初始结构性参数（构度）和剪切过程结构性参数（应力比结构性参数）定义了可综合描述从土的初始结构状态到平面应变剪切破坏状态的全过程结构性参数，分析了平面应变条件下，全过程结构性参数随轴向应变的衰减演化规律及结构性强度特性。(3)通过不同含水率黄土的加、卸载平面应变试验结果的对比，分析了不同应力路径条件下原状黄土的强度和变形特性差异，为平面应变条件下本构模型的建立奠定了基础。试验结果表明，应力路径的的变化不仅影响黄土的强度特性，而且影响剪切过程中变形的发展，具有不同的变形规律；围压增大增强了黄土的压硬性，提高了土的强度；含水率增大软化了黄土的结构，削弱了土的强度。平面应变条件下土的强度比常规三轴条件下的强度大1.1～1.5倍；侧向卸载条件下土破坏时的应变比平面应变竖向加载和常规三轴试验小。(4)以黄土的平面应变试验为基础，建立了平面应变条件下土的屈服面，以及屈服面随黄土压缩结构屈服和塑性体应变发展的运动规律；进而，应用关联流动法则，建立了平面应变弹塑性本构模型。研究成果可深化平面应变条件下黄土力学性质的认识，为完善平面应变条件下黄土工程建设的设计和变形评价方法提供有力的理论基础和试验依据。