基于CT图像和机器学习的钙质砂宏微观力学试验及多尺度离散元建模

The micro-structures of calcareous sand particles (e.g., composites, size and shape), at microscale, have great influences on particle strength and particle breakage pattern, and at macroscale, make essential impacts on the mechanical behavior of calcareous sand bulks, leading to complex macroscopic physical and mechanical properties. Based on laboratory experiments and multiscale discrete element modeling, and using particle breakage and fragments evolution as a bridge, this project aims at developing a quantitative relationship between the micro-structure characteristics of calcareous sand particles and the bulk physical and mechanical properties of calcareous sand bulks. To begin with, a framework for reconstructing and characterizing granular particles from X-ray computed tomography is developed based on machine learning technique and level set method. Then, multiscale discrete element models that incorporate realistic micro-structures of calcareous sand particles are created for simulating the breakage tests of individual particles and the three-dimensional compression tests of bulks, respectively. The microscopic discrete element model passes particle strength and fragment characteristics up to the discrete element model at macroscale. Laboratory experiments are also conducted to calibrate and validate the proposed multiscale discrete element models. Lastly, the effects of particle micro-structures on the mechanical behavior of calcareous sand bulks are investigated based on the results of a serial of discrete element simulations with various particle micro-structures and loading conditions. The research work of this project would promote the study on particle micro-structures and multiscale discrete element modeling of calcareous sand, and provide useful implications for optimizing the design, construction and maintenance of calcareous sand foundations.

钙质砂的微观结构（如颗粒的微观组成、尺寸及形态）在微观尺度影响着颗粒的强度及破碎规律，在宏观尺度影响着堆积体的力学行为，进而导致复杂的宏观物理力学特性。本项目旨在以颗粒的破碎及形态演化为桥梁，通过宏微观力学试验及多尺度离散元模拟，建立微观结构对宏观物理力学特性影响的定量规律。首先利用micro-CT技术并基于机器学习和水平集方法构建钙质砂的微观重构与量化表征的流程框架；然后根据钙质砂的真实微观结构，通过颗粒的强度及碎块的形态分布特征相关联，建立颗粒及堆积体的多尺度离散元模型，并基于室内的单颗粒压缩破碎试验及堆积体三维剪切试验对模型进行校准与验证；最终，通过模拟颗粒及堆积体在不同微观结构及不同荷载条件下的力学响应，系统性地研究微观结构与宏观物理力学特性之间的量化关系。本项目有助于发展钙质砂的三维微观结构及多尺度离散元建模研究，为钙质砂工程基础的设计、施工及维护提供理论和技术支持。

钙质砂具有形态不规则、多内部孔隙等特点，其带来的不良工程特性影响着南海岛礁地区的基础设施建设及能源开采等问题。有鉴于此，本项目通过室内力学试验及离散元模拟，研究钙质砂力学特性的微观机理及其形态效应影响。开展了1）钙质砂的颗粒微观重构和表征、2）钙质砂的宏微观力学试验、3）钙质砂的离散元建模及模拟分析等方面内容研究。实现了构建钙质砂的微观重构和量化表征方法、揭示颗粒破碎的微观机理和形态演化规律、建立考虑钙质砂真实微观结构的离散元模型等预期研究目标，完善了对钙质砂复杂力学行为的微观机理认识及数值分析方法。研究成果一方面可用于钙质砂的力学机理研究，为岛礁基础设施建设与能源开采工程提供理论和技术支持；另一方面积累的离散元关键算法和自主研发的离散元程序，为将来研发适用于复杂颗粒材料的新一代国产化离散元仿真软件奠定了扎实基础。依托本项目资助和研究成果，目前已发表学术论文及论著11篇，其中SCI收录9篇、EI收录1篇、中文核心1篇；申请发明专利5项、已授权发明专利3项，授权软件著作权1项；获得科研及科技奖励5项；参与国内外学术会议交流5次；协助培养硕士研究生2名、博士研究生1名。

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