土体介质多尺度耦合力学特性的理论与试验研究

发布时间：2018-07-01 13:54

  本文选题：微重比 + 土体胞元模型　； 参考：《华南理工大学》2016年博士论文

【摘要】：土体介质是地质循环作用下由固体颗粒、孔隙液体和孔隙气体组成的多相地质材料,土体不同尺度土颗粒之间形成的复杂微细观结构和组构以及各相物质之间的相互协作用,导致土体在不同尺度结构层次呈现不同的物理机制和力学响应,突显土体强度和变形特性的多层次耦合和跨尺度演化效应。本文以黏性土为研究对象,采用理论分析和试验研究相结合的方法探讨土体介质的多尺度耦合力学特性,理论分析主要是阐述土体介质不同尺度结构层次上力学机制的多样性和耦合性并建立能够模拟和预测土体介质多尺度耦合力学特性的力学模型和本构关系;试验研究则主要是呈现土颗粒粒径和相对含量对土体抗剪强度的影响规律并求解力学模型和本构关系的微细观计算参数。在这两个方面的工作基础之上,综合分析具有多尺度分层次理论框架的力学模型和本构关系中微细观计算参数的物理意义并通过试验结果评估理论的适用性和有效性。最后,将提出的多尺度研究框架与传统土力学强度理论相结合,以详细解释土体介质强度特性的颗粒尺度效应。本文开展的研究工作和取得的研究成果主要有以下几个方面:(1)通过分析不同尺度土颗粒之间各种力场的相互作用效应,提出微重比的概念,定量计算土颗粒之间的范德华力和库仑力等微观作用力,建立土颗粒微重比与其粒径的关系,计算结果表明,当土颗粒粒径小于10μm时,反映黏聚效应的微观力相互作用十分显著,随着土颗粒粒径的继续增加,反映摩擦效应的重力作用开始显现。因此,土颗粒的微重比可作为划分基体颗粒和加强颗粒的客观物理依据。(2)根据不同尺度土颗粒相互作用产生的黏聚和摩擦物理效应,构建能够反映土体内部材料信息和颗粒特征信息的细观土体胞元,以协调微裂纹密度和应变梯度分别描述土体的微细观结构变形特征,利用不同尺度层次间的能量平衡原理和几何变形相容性条件建立能够模拟和预测土体介质多尺度耦合力学特性的土体胞元模型,比较土体胞元模型对土体屈服应力的预测结果与试验结果,初步证实了土体胞元模型的适用性和有效性,在此基础之上,导出具有多尺度分层次理论框架的土体增量本构模型,以此对无侧限压缩试样的塑性应变分布进行分析,结果表明,基于土体胞元模型的增量本构关系能够有效地描述土体力学特性的颗粒尺度效应和多尺度耦合机制。(3)制备一系列具有不同加强颗粒组合和基体液性指数的土体胞元模型试样,分别进行直接快剪试验和三轴压缩试验。试验结果呈现了加强颗粒粒径和体分比对土体抗剪强度的影响规律:当加强颗粒体分比小于0.271时,土体的抗剪强度随加强颗粒粒径和体分比的变化而改变:对于三轴固结/不固结不排水剪切试验,土体的抗剪强度随加强颗粒的粒径减小和体分比增加而显著提高;对于直接快剪试验,土体的抗剪强度随加强颗粒体分比的增加而提高,但随加强颗粒粒径的变化而基本保持不变。当加强颗粒体分比大于0.318时,无论是三轴压缩试验还是直接快剪试验,土体的抗剪强度不再随加强颗粒体分比的变化而改变,呈现加强颗粒增强效应的临界现象。土体胞元模型的理论与试验研究表明,加强颗粒体分比增加诱发土体细观组构发生物质相变是加强颗粒体分比增强效应出现临界值的根本原因。(4)结合土体胞元模型的理论分析与试验研究,土体力学特性颗粒尺度效应的作用机制可以解释为:基体与加强颗粒之间的不相容变形,微观上导致协调微裂纹的产生,细观上诱发土体胞元应变梯度的出现,协调微裂纹密度和应变梯度则增加了单位体积土体中消耗或储存的能量,进而使土体的变形阻力增大,宏观上表现为土体具有更强的变形性能和更高的抗剪强度。(5)在土体胞元模型的基础上,考虑了土体胞元内部加强颗粒的转动梯度对土体强度特性的影响,推导体现土体介质力学特性颗粒尺度效应的屈服应力计算公式,结合传统土力学强度理论,建立多尺度Mohr-Coulomb强度准则,根据试验结果绘制其屈服轨迹并与传统Mohr-Coulomb强度准则的屈服轨迹进行比较,结果表明,多尺度Mohr-Coulomb强度准则能够较好地模拟和预测土体介质强度特性的颗粒尺度效应和多尺度耦合机制,而且可以较好地与传统土力学强度理论相结合。
[Abstract]:Soil medium is a multi-phase geological material composed of solid particles, pore liquid and pore gas under the action of geological cycle. The complex microstructure and structure of soil particles in different scales and the interaction between each phase matter, resulting in different physical mechanism and mechanics of soil in different scale structure levels. In response, the multi-layer coupling and cross scale evolution effect of soil strength and deformation characteristics are highlighted. In this paper, the multi-scale mechanical properties of soil medium are discussed by combining theoretical analysis with experimental research. The theoretical analysis is mainly about the mechanical mechanism of soil body medium at different scale structure levels. The mechanical model and constitutive relation can be established to simulate and predict the mechanical properties of multi scale coupling in soil medium. The experimental study is mainly about the effect of the particle size and relative content of soil on the shear strength of soil and the calculation parameters of the mechanical model and the constitutive relation in the two aspects. On the basis of the work, the mechanical model of the multi scale hierarchical theoretical framework and the physical meaning of the calculation parameters in the constitutive relation are synthetically analyzed and the applicability and effectiveness of the theory are evaluated through the experimental results. Finally, the proposed multi scale research framework is combined with the traditional soil strength theory to explain the soil medium in detail. The research work and results obtained in this paper mainly include the following aspects: (1) by analyzing the interaction effects of various force fields between different scales of soil particles, the concept of micro gravity ratio is proposed, and the microcosmic forces such as Vander Ed Ley and Coulomb force between soil particles are calculated and the soil is established. The relationship between the particle microweight ratio and the particle size shows that when the particle size is less than 10 m, the micro force interaction which reflects the cohesive effect is very significant. With the continuous increase of the particle size of the soil, the gravity action reflecting the friction effect begins to appear. Therefore, the micro weight ratio of the soil particles can be used as a matrix particle and a strengthening particle. (2) in accordance with the physical effects of cohesive and friction produced by the interaction of soil particles in different scales, a mesoscopic soil element can be constructed which can reflect the information of the material and the characteristics of the particles in the soil. In order to coordinate the micro crack density and strain gradient, the microstructural deformation characteristics of the soil are described respectively, and the different scales are used to make use of the different scales. Based on the principle of energy balance and the compatibility condition of geometric deformation, the soil cellular element model which can simulate and predict the multi scale coupling mechanical properties of soil medium is established, and the prediction results and experimental results of soil cell element model on soil yield stress are compared, and the applicability and effectiveness of the soil cellular element model are preliminarily confirmed. The soil incremental constitutive model with multi scale hierarchical theoretical framework is developed to analyze the plastic strain distribution of unconfined compression specimens. The results show that the incremental constitutive relation based on the cellular element model can effectively describe the particle size effect and multi-scale coupling mechanism of soil mechanical properties. (3) a series of materials are prepared. The experimental results show that the influence of particle size and body ratio on the shear strength of soil is enhanced by direct fast shear test and three axial compression test. As for the three axis consolidation / unconsolidated undrained shear test, the shear strength of the soil increases significantly with the increase of the particle size and the volume ratio. For direct fast shear test, the shear strength of the soil increases with the increase of the particle ratio, but it is basically guaranteed with the increase of particle size. When the particle ratio is greater than 0.318, both the three axis compression test and the direct fast shear test, the shear strength of the soil no longer changes with the increase of the particle ratio, and presents the critical phenomenon of strengthening the particle enhancement effect. The fundamental reason for strengthening the critical value of the particle ratio enhancement effect is the phase transition of the meso microstructure of the soil. (4) combining the theoretical analysis and experimental study of the soil cell element model, the mechanism of the particle size effect of the soil mechanical properties can be explained as: the incompatible deformation between the matrix and the strengthening grain, and the microcosmic coordination micro The occurrence of the crack is induced by the microcrack density and the strain gradient, which increases the energy consumed or stored in the unit volume soil, and then increases the deformation resistance of the soil. On the macroscopic view, the soil has stronger deformation property and higher shear strength. (5) in the soil element model of soil mass On the basis of this, the influence of the rotational gradient of the soil element on the strength characteristics of the soil is considered, and the formula of yield stress is derived, which embodies the particle size effect of the mechanical properties of the soil. In combination with the traditional soil mechanics strength theory, the multi scale Mohr-Coulomb strength quasi rule is set up. The yield trajectory of the Mohr-Coulomb strength criterion is compared. The results show that the multi-scale Mohr-Coulomb strength criterion can better simulate and predict the particle size effect and multi scale coupling mechanism of soil medium strength characteristics, and it can be better combined with the traditional soil mechanics strength theory.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU43
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本文编号：2087995