动静荷载作用下钙质砂颗粒破碎机理和本构关系研究

Reef island project construction is the major national strategy requirement for the improvement of ocean resources exploration and maritime defense abilities in South China Sea. Calcareous sand is widely distributed in the region around the South China Sea and considered to be the most suitable geomaterial for reef island reclamation. Under larger monotonic and cyclic loadings, breakage of calcareous sand grains would cause excessive deformation of ground, leading to reef island project disaster. Therefore, revelation of particle crushing mechanism is the critical scientific issue for safe reef island project construction. The main research contents of this project are shown as follow:① A series of monotonic and cyclic triaxial shear tests are intended to be performed to investigate the particle crushing properties of calcareous sand, and describe the evolution law of particle crushing and the characterization of crushing pattern.② The influence of particle crushing on the macro-mechanical strength, deformation and liquefaction properties is investigated. The evolution laws of grain shape and micro-structure of calcareous sand with the development of particle crushing are clarified. The particle crushing mechanisms of calcareous sand under monotonic and cyclic loadings are revealed.③In combination of experimental results obtained from this project, the subloading surface theory and a combined isotropic and kinematic hardening parameter are also introduced into the previously established constitutive model. A new constitutive model with the capacity of describing the monotonic and cyclic shear characteristics and the evolution of grading curves of calcareous sand is proposed. This research project provides theoretical reference and technical support for the safe and stable design theory of reef island construction infrastructure in South China Sea.

岛礁工程建设是提升我国南海资源开发和海上国防能力的国家重大战略需求。钙质砂广泛分布于南海区域，是吹填筑岛的首选材料。在较大动静荷载作用下，其颗粒会发生破碎，甚至会导致地基过大变形进而引发岛礁工程灾害。因此，揭示钙质砂颗粒破碎机理是岛礁工程安全建设中亟待解决的关键科学问题。本项目主要研究内容如下：①开展大量动静三轴试验,研究钙质砂颗粒破碎特性，描述颗粒破碎演化规律及其表征样式；②从宏观上探明颗粒破碎对钙质砂液化和静力特性的影响，从微观上阐明颗粒破碎发展过程中颗粒形状的演变规律，揭示钙质砂在不同荷载形式下的颗粒破碎机理；③基于三轴试验数据，在原有考虑破碎影响的静力本构模型基础上，结合下负荷面理论和混合硬化参数来考虑动力加载，同时引入破碎量表征临界状态线的变化，提出一个能够描述钙质砂静动力学特性和级配演变规律的弹塑性本构模型。本项目将为我国南海岛礁工程基础设施的安全建设提供理论参考和技术支持。

钙质砂是南海岛礁工程吹填建设的重要地基材料。在多类型荷载作用下，钙质砂会发生颗粒破碎现象，进而显著影响钙质砂地基的承载性能。本项目综合运用试验和理论分析研究方法，针对钙质砂开展不同条件下的排水和不排水静动三轴剪切试验，揭示颗粒破碎机理并查明其对力学行为的影响机制。开展了终止于不同加载阶段的高压一维压缩试验，查明颗粒破碎的演化规律及其对压缩特性的影响规律。本项目的重要研究结果如下。. 首先，针对南海钙质砂开展系列排水和不排水动静三轴试验，研究了不同荷载形式下钙质砂试样的破坏模式，定量分析了加载后试样的颗粒破碎程度，揭示了颗粒破碎对钙质砂强度、孔隙水压和变形特性的影响规律。基于动静三轴试验结果，建立了钙质砂不排水动静强度关联方程。其次，借助图像分析技术，定量表征了钙质砂颗粒的多种类形貌参数，开展了多组终止于不同应力水平的高压一维压缩试验，探究了颗粒破碎后钙质砂颗粒形貌的演化规律，查明了颗粒破碎对钙质砂压缩特性和微观颗粒结构以及形貌演化的影响机制。探明了钙质砂等颗粒材料的临界状态强度指标和颗粒形貌参数的关联机制。基于本项目和其他颗粒材料的试验结果，建立一个能够考虑颗粒破碎影响的砂土本构模型，该模型能够描述砂土在广应力范围的力学响应规律。本项目研究结果可为动荷载作用下岛礁工程设施的安全设计和长期服役提供理论依据和技术支持。.