基于实时加载CT扫描的钙质砂宏细观力学机制与本构模型研究

Like other natural geo-materials, carbonate sand exhibits high angularity, inner pore structure and crushable, which have a great effect on the mechanical behavior of non-linear deformations and strength. In classic soil mechanics theory, the influence of variations of particle breakage on micro-structure and deformation under elevated loading cannot be studied. A deep understanding in micro characteristics and deformation mechanisms of carbonate sand is an important topic to be solved urgently. In this project, preliminary tests on carbonate sands have been done, showing that the particle shapes and internal structures of carbonate sands are varied after being subjected to particle breakage. A hypothesis that there is a function correlation between micro-structure parameters and non-linear deformation is proposed. High performance particle imaging analysis, real-time CT scanning oedometer tests and high pressure tri-axial tests will be used to study the non-linear deformation characteristics, the evolutions of particle shape, pore size distribution under elevated loadings for different particle shapes, gradations and densities specimens. From the experiment results, the non-linear characteristic of carbonate sand under loading will be statistic and evaluated by the fractal theory. The multi-scale correlation between the micro properties and the non-linear deformations will be established. Based on the critical state theory, a novel constitutive model with consideration of influence of micro characteristics will be developed eventually. The outcomes of this project will be helpful to provide broad the knowledge of micro-mechanics, and will make significant contributions to support the advancement of design approach and optimize the land reclamation design and construction.

钙质砂除了具备天然岩土材料的基本性质外，还具有颗粒高棱角性，含内孔隙结构和易破碎等特性，对其宏观力学行为，尤其是颗粒破碎下的变形和强度影响巨大，经典土力学理论无法对此进行量化描述。因此，研究钙质砂的细观结构特性及其变形破坏演化机理是当前迫切需要解决的重要课题。项目从预试验中发现的钙质砂“颗粒破碎”特征现象出发，提出钙质砂细观结构参量与宏观非线性变形存在函数相关性的科学假说；利用高精度颗粒图像分析、CT实时扫描固结试验及高压三轴试验，研究不同颗粒形貌、级配和密实度的钙质砂在颗粒破碎下的变形特性，揭示颗粒形貌、孔隙排列随荷载演化的规律；结合分形理论，发展符合钙质砂细观特征的表述方法，构建钙质砂结构参量与非线性变形的多尺度关联。进而基于临界状态理论，建立新的宏细观结合的钙质砂非线性变形的损伤本构模型。本项目研究成果有助于丰富钙质砂细观力学知识，为完善吹填岛礁设计理论和加固技术提供理论支撑。

钙质砂颗粒破碎前后的颗粒细观参数对其力学性质的影响是正确认识钙质砂力学特性的前提。因此，本项目采用室内试验研究和理论研究等手段，从吹填岛礁的受力特点和钙质砂颗粒破碎的细观特性展开了研究，针对钙质砂在颗粒破碎情况下的非线性变形及其颗粒形貌的演化等进行了深入的研究，从吹填岛礁的受力特点和钙质砂颗粒破碎的细观特性展开了研究，探讨了不同粒径钙质砂颗粒破碎对珊瑚砂强度和残余应变发展的影响。主要得到包括以下几点内容：.（1）在室内试验层面，针对不同粒径的均匀级配珊瑚砂，进行了固结试验，三轴试验和大剪切位移的环向剪切试验，固结试验研究了不同粒径珊瑚砂的非线性变形演化，三轴和环剪试验着重研究了颗粒破碎对珊瑚砂的剪胀性，峰值强度，残余强度与应变发展的影响，同时也对环剪试验之后土样的颗粒形状分析。.（2）在理论分析层面，颗粒数量计算分形维数时，由于颗粒破碎后的自相似性和无尺度性，其分形维数不随计算颗粒数量是假定的颗粒形状而变化，仅仅计算得出颗粒数量减少，其分形维数基本无变化，并且在推导了含有分形维数的本构模型，通过试验验证了其有效性。.