钙质砂破碎行为本质与微生物固化的微观力学机理研究

Carbonate sand is the main filling material in the reef construction of the South China Sea. Due to the complex particle morphology and rich internal pore structure, the outstanding particle crushing results in an adverse influence on the engineering mechanical properties of carbonate sand. Therefore, it promotes a well application prospect of microbially induced calcite precipitation (MICP) for the reinforcement of carbonate sand. However, the underlying mechanism by which the particle microstructure affects the particle crushing behaviors and the bio-cementing mechanism of MICP for carbonate sand are not well understood so far. For this reason, in this project, we will propose to identify, reconstruct and characterize the particle morphology, internal pore structure and MICP cementation structure by means of high-precision X-ray micro-tomography (μCT) scanning, image processing and spherical harmonic analysis. The single particle crushing test, micro-triaxial test with in-situ X-ray μCT scanning and combined finite-discrete element method will be mainly used in this research. By using these methods, the effect of the particle morphology, internal pore structure and MICP cementation structure on the micromechanics of particle crushing behaviors including particle fracture mode and crushing strength, fragment grading and morphological evolution, shear bond development, energy dissipation mechanism, etc., will be detailedly studied. Meanwhile, the microscopic damage mechanism of MICP cementation structure and its reinforcing effect on particle crushing behaviors will be deeply investigated. These results and findings will provide us a deep insight into the micromechanical nature of particle crushing behaviors and the micromechanism of MICP cementation for carbonate sand.

钙质砂是南海岛礁工程建设中的主要填筑材料，由于其颗粒形态复杂，内孔隙结构丰富，导致其颗粒破碎现象显著，工程力学性质不佳，因此开拓了微生物诱导方解石沉淀（MICP）技术固化钙质砂的应用前景。然而，目前对钙质砂的破碎行为本质及其MICP固化的内在机理尚缺乏足够的认识。鉴于此，本项目将借助于高精度的X射线微型计算机断层（μCT）扫描、图像处理和分析技术、球谐函数分析，实现钙质砂三维颗粒形态、内孔隙结构与MICP胶结结构的识别、重建与表征。通过颗粒单轴压碎试验和原位μCT扫描支持下的微型三轴试验，并结合连续-离散耦合分析方法，细致研究颗粒形态、内孔隙结构和MICP胶结结构对钙质砂破碎过程中颗粒破碎模式和破碎强度、碎片级配和形态演化、剪切带发展和能量耗散机制等微观力学行为的影响，深入探究MICP胶结结构的微观损伤机制及其对颗粒破碎性能的增强效应，揭示钙质砂破碎行为本质与MICP固化的微观力学机理。

钙质砂是南海岛礁工程建设中的主要填筑材料，由于其颗粒形态复杂，内孔隙结构丰富，导致其颗粒破碎现象显著，工程力学性质不佳。此外，由于岛礁工程的特殊施工条件以及临近海域的生态环保要求，提出了绿色环保的微生物诱导方解石沉淀（MICP）技术实现钙质砂的加固与应用。然而，目前对钙质砂的破碎行为及其MICP固化机理尚缺乏足够的认识。鉴于此，本项目借助高精度的X射线微型计算机断层（μCT）扫描、图像处理与分析技术实现了钙质砂三维颗粒形态、内孔隙结构与MICP胶结物的识别、重建与表征。对钙质砂内孔隙结构连续孔径分布的统计分析发现了其与生物、地质成因的内在关联，并构建了钙质砂细观结构的综合分类体系。项目研制了适用于μCT平台的轻型单轴和三轴试验装置，通过原位扫描对钙质砂颗粒破碎行为进行了实时观测，并于基于μCT影像数据在连续-离散耦合模拟和离散元模拟中构建了钙质砂真实细观结构的精细化建模方法，综合考虑了矿物组分、颗粒形态和内孔隙结构影响颗粒破碎行为的耦联机制，从微细观尺度上探究了钙质砂颗粒的裂纹扩展、压碎强度和破碎模式的差异性，厘清了颗粒形态与内孔隙结构对散粒土颗粒破碎性能的影响机制。研发了相应的MICP固化工艺，通过试验分析证实了MICP 技术对钙质砂物理力学性能的的改善作用。鉴于钙质砂破碎性能显著，项目创新性地指出了MICP 技术对钙质砂颗粒抗破碎性能的增强作用，通过MICP 固化钙质砂颗粒的压碎试验与SEM 扫描发现生成的方解石沉淀不仅在钙质砂颗粒表面形成包裹与胶结作用，也在颗粒体内孔隙中形成充填作用，从而显著地提升钙质砂颗粒破碎强度并改善其破裂模式，从微细观尺度上揭示了MICP 固化钙质砂的内在机理。依托本项目共发表SCI/EI论文12篇，授权发明专利和软件著作权2项，获湖北省自然科学二等奖，研究成果为南海岛礁工程的长期性能改善、防灾能力提升与生态环境保护提供了强有力的理论依据与技术支持。