胶结性砂土在复杂应力状态下的微观损伤机制

Natural soils are often cemented and there has been a need to understand better and properly model their behaviour for the safe design and assessment of critical infrastructure. However, current research mostly focused on the macro-mechanics of cemented sands. Studies on breakage behaviour as well as the micro-constitutive relation of cemented sands at particle scale are limited. Besides, the influencing factors on the micro-mechanical response of cemented particles are not clear. These restrict the understanding of cemented sands in multiple scales and necessitate the study of cemented soils at the scale of the grain. In this study, a series of complex loading path tests would be conducted on two natural sand grains cemented with an artificial bonding component by means of a novel apparatus, which gives the opportunity to obtain insights into the micro-mechanics of cemented soils and contribute to the development of more accurate models to be utilized in the discrete element analysis of geo-materials. Taking the particle morphology, particle breakage behaviour as well as the characteristics of the bond into consideration, this project aims to explore the failure behaviour and the mechanical response of contact model. Then propose constitutive model for the cemented particle under different loading paths at particle scale. Finally, discuss the optimal failure criterion and reveal the micro-mechanics and damage mechanism for cemented sands.

胶结砂作为常见岩土材料应用广泛，其力学特性与实际工程质量紧密相关。然而，目前相关研究集中在宏观层面，我们对颗粒尺度下胶结砂的破碎行为、微观力学响应和本构关系及其影响因素认识有限，难以掌握胶结砂等结构性土体多尺度损伤机制。因此本项目将以使用天然土工材料制备的人工胶结砂颗粒模型为研究对象，利用自主设计改造的试验装置，在考虑颗粒形态特征、颗粒破碎和胶结性质等影响因素的情况下，通过一系列微观复杂荷载试验，并结合离散元法数值模拟计算手段，阐明胶结砂接触模型的破碎行为和力学响应，建立不同应力状态下胶结砂在颗粒尺度下的本构关系，确定最适颗粒破坏准则，旨在揭示胶结砂的微观力学机理和损伤机制，为结构性土体多尺度力学机理研究及工程建设提供科学依据。

胶结砂作为常见岩土材料应用广泛，其力学特性与实际工程质量紧密相关。然而，目前相关研究集中在宏观层面，我们对颗粒尺度下胶结砂的破碎行为、微观力学响应和本构关系及其影响因素认识有限，难以掌握胶结砂等结构性土体多尺度损伤机制。具体表现在缺乏考虑颗粒形态、颗粒破碎、胶结特性等微观性质对胶结砂宏观力学行为的影响，缺少可靠的微观力学实验数据对模拟计算进行支撑。本项目利用石英砂、石膏和水泥等天然岩土材料制备微观双珠胶结接触模型，并设计开发了一套微观双轴加载设备，对模型进行受压、纯剪、弯剪等一系列复杂荷载试验。试验过程中借助显微摄像机建立了胶结砂颗粒在复杂荷载下微观力学行为的分析和归类，结果发现：1.利用石膏作为胶结材料制备的双珠胶结模型的试验结果一致性相较于水泥更高，试验的可重复性更好；2.在轴压试验中，双珠胶结模型产生了三种不同的破碎模式，颗粒破碎可能先于整体破坏前出现，但是胶结层破坏对整体破坏起到控制性作用；3.在轴压下，砂颗粒局部圆度对胶结模型的强度产生重要影响；4.纯剪试验中，胶结层与颗粒在剪力作用下脱开是导致胶结模型破坏的主要原因；5.弯剪应力状态下，会出现胶结层的剪切破坏，这对胶结模型整体强度起到控制作用。除了微观试验，本项目针对胶结砂还进行了一系列宏观三轴试验，分别探究了粒径大小、围压、石膏掺入比、颗粒级配、养护条件等不同因素对胶结砂峰值抗剪强度、内摩擦角和粘聚力的影响变化规律。将微观试验中得到的接触参数应用于离散元数值模拟分析，模拟结果显示与三轴试验结果高度一致，证实采用真实砂颗粒制作的胶结模型得出的微观力学参数对于离散元模拟分析具有极高的准确性和参考价值，可为离散元模拟中接触粘结参数的标定提供经验和依据，进而从宏观到微观建立多尺度的胶结砂破坏的损伤机制。