不同应力路径下重塑黄土的强度和变形特性试验研究

发布时间：2018-06-14 17:14

本文选题：重塑黄土 + 应力路径　；参考：《长安大学》2017年硕士论文

【摘要】：黄土具有疏松多孔、弱胶结的特殊结构,在我国西北地区广泛分布。随着“一带一路”西北战略区的经济发展建设,与黄土相关的人类活动日益频繁,形成了大量黄土堆填边坡。诸多学者开展有关黄土的力学特性研究,基于这一层面解释成灾机理,为黄土地区的防灾减灾工作的开展起到积极的作用。为研究黄土堆填体的变形破坏规律,本文在借鉴前人研究的基础上,依据黄土堆填边坡的受力特征,以重塑黄土为研究对象,设计不同应力路径的三轴试验,包括常规三轴压缩试验(CTC)、平均主应力为常数的三轴压缩试验(TC)、减围压的三轴压缩试验(RTC),研究不同应力路径对重塑黄土力学特性的影响,并通过SEM图像分析微观结构特征,分析黄土堆填体的破坏发展规律,进而解析黄土的灾变力学行为。得出结论如下:(1)黄土的强度特性:CTC路径下重塑黄土表现为应变硬化型,TC、RTC路径下呈应变弱硬化,同一固结围压下土体抗剪强度CTC路径TC路径RTC路径。应力循环的加载方式相比单调加载,土体被压密,因而抗剪强度稍有提高。(2)黄土的变形规律:重塑黄土属于亚稳定结构土,在变形破坏过程中整体表现为体积收缩,CTC、TC、RTC试验路径的体缩量逐渐减小;对于同一应力路径,体缩量随初始围压的增大而增大。土体的变形同时存在剪缩和剪胀两部分塑性变形,重塑黄土在较低应力水平下的加载-卸载-再加载循环中表现为加载体缩,卸载时因剪胀部分的恢复而表现为体缩,较高应力水平下则表现为加载体缩卸载体胀。(3)微观结构特点:不同应力路径剪切后,按CTC、TC、RTC顺序,颗粒破碎程度依次减小,孔隙含量依次增大。(4)重塑黄土的屈服模型描述:引用殷宗泽提出的椭圆-抛物线双屈服面塑性模型,依据试验结果对模型参数取值进行调整,经计算,该模型能够较好地描述重塑黄土变形特性。(5)黄土灾变力学行为分析:在加载作用下,变形初期,土体被压缩挤密,其强度在一定程度上得到提升,随着荷载的持续增加,变形速率平稳增大,土体变形至破坏呈渐进式发展,以轴向压缩变形为主,侧向鼓胀变形较小;对于侧向卸荷形式的变形行为,卸荷初期,土体维持在相对稳定的状态,变形量很小,当侧向约束减小到一临界状态后,结构失稳破坏,短时间内土体变形迅速发展,变形速率迅速增大。
[Abstract]:Loess has a special structure of porous and weak cementation, which is widely distributed in northwest China. With the economic development and construction of "Belt and Road" northwest strategic area, human activities related to loess become more and more frequent, forming a large number of loess landfills slope. Many scholars have carried out researches on the mechanical properties of loess, based on which the mechanism of disaster formation has been explained, which plays an active role in the development of disaster prevention and mitigation in loess area. In order to study the deformation and failure law of loess landfills, based on the previous research, according to the stress characteristics of loess landfill slope, this paper designs triaxial tests of different stress paths, taking remolded loess as the research object. Including conventional triaxial compression test (CTC), triaxial compression test with constant mean principal stress (TCC) and triaxial compression test (RTC) with reduced confining pressure. The effects of different stress paths on the mechanical properties of remolded loess are studied, and the microstructure characteristics are analyzed by SEM images. The failure and development law of loess landfill is analyzed, and the catastrophic mechanical behavior of loess is analyzed. The conclusion is as follows: (1) the strength characteristics of loess are as follows: (1) the remolded loess under the: CTC path is shown as strain hardening under strain hardening type TCU RTC path, and the soil shear strength CTC path is TC path RTC path under the same consolidation confining pressure. Compared with monotone loading, the loading mode of stress cycle results in the compaction of soil mass, so the shear strength is slightly increased.) the deformation law of loess is that the remolded loess belongs to the substable structure soil. In the process of deformation and failure, the volume shrinkage of CTCU TCU RTC test path decreases gradually, and for the same stress path, the volume shrinkage increases with the increase of initial confining pressure. At the same time, there are two parts of plastic deformation in soil deformation: shear shrinkage and dilatancy. In the load-unload reloading cycle of remolded loess at lower stress level, it is shown as carrier shrinkage, and when unloading, it is shown as bulk shrinkage due to the recovery of shear expansion part. At higher stress level, the microstructural characteristics of the loading carrier are as follows: after shearing with different stress paths, the degree of particle breakage decreases according to the order of CTCU TCU RTC, and the degree of particle breakage decreases in turn after shearing under different stress paths. The yield model of remolded loess is described by increasing porosity content in turn. The plastic model of elliptic-parabola double yield surface proposed by Yin Zongze is quoted. The parameters of the model are adjusted according to the test results, and the model parameters are calculated. The model can well describe the deformation characteristics of remolded loess. (5) Analysis of the catastrophic mechanical behavior of loess: under the action of loading, the soil is compressed and compacted at the initial stage of deformation, and its strength is improved to some extent, and the strength increases with the continuous increase of load. When the deformation rate increases steadily, the deformation to failure of soil develops gradually, mainly axial compression deformation, while lateral bulging deformation is small. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the initial unloading stage. The deformation is very small, when the lateral constraint is reduced to a critical state, the structure loses stability and failure, the soil deformation develops rapidly in a short time, and the deformation rate increases rapidly.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU444

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