南海钙质粉砂的干缩机制及抗裂加固方法研究

Drying shrinkage can be found in calcareous silt, which is different from terrigenous silt. Drying shrinkage leads to decrease of integrity of silt, what’s more, the infiltration of rainwater and seawater may contribute to the destruction. It threatens the long-term stability of engineering structures of on the reefs. The project focuses on this engineering problem, the drying shrinkage phenomenon in hydraulic fill project is used as a enter point, the micro-structure characterization and macro-mechanical properties are fixed as the leading clue. The drying shrinkage process of calcareous silt, the silt-water interaction and the change of mineral pattern during drying process is quantitatively analyzed by methods of X-ray diffraction analysis, imaging of SEM, shrinkage test. The mineralogical, physical and mechanical mechanism is revealed how drying shrinkage of calcareous silt lead to the decrease of strength and stability. The laboratory model experiments are carried out to simulate the drying shrinkage process, through which the characteristic of drying shrinkage is described quantitatively and the generation together with evolution rule of crack are analyzed. The generation and evolution process of crack is analyzed and predicted based on the consolidation theory of unsaturated soil. At last, the improve measures and foundation treatment methods are presented by restraining drying shrinkage. The research of this topic provides essential scientific basis and technical support for hydraulic fill project in South China Sea.

钙质粉砂与陆源粉砂不同，会发生干缩开裂现象，而干缩裂缝的产生通常会引起土体整体性降低，降雨、海水等的入渗更会加剧土体破坏，从而对岛礁工程构筑物的长期稳定性构成威胁。本项目针对这一工程问题，以南海珊瑚岛礁吹填造陆工程中积水区沉积的钙质粉砂的干缩开裂现象为切入点，将其微、细观结构特征和宏观力学特性作为研究主线，通过X-射线衍射分析、扫描电镜成像、收缩试验等方法定量分析钙质粉砂失水收缩过程及土-水相互作用机制，揭示钙质粉砂由于失水收缩导致强度和稳定性降低的矿物学、物理学及力学机制；通过室内模型试验模拟干缩开裂过程，对干缩开裂特征进行定量描述，分析裂缝产生和演化的规律以及内在原因；以非饱和土固结理论为基础，开展裂缝产生和发育过程的分析、预测；最终，以抑制土体失水收缩作为裂缝控制的主要手段，提出钙质粉砂的改良措施和地基处理方法。本课题的研究可为南海吹填造陆工程及地基处理提供必要的科学依据和技术支撑。

南海钙质粉砂发生的干缩开裂现象会导致地基土体的整体性降低，继而发生的雨水、海水入渗，会进一步加剧土体的破坏，对岛礁工程的长期稳定性产生不利影响。本项目通过对钙质粉砂原位地质环境、海洋环境的调查， 宏观甄选出含水率、环境温度、土体盐度等主要致裂因素；通过X-射线衍射、偏光显微镜等微观试验技术、模型试验、强度试验等物理力学试验手段，揭示了矿物组成、含水率、环境温度、土体盐度、失水速率等因素与干缩裂缝演化的相关性；通过数字图像处理技术对干缩裂缝图像进行分析，量化了环境条件对钙质粉砂干缩裂缝的影响程度；此外，对致裂因素的影响程度进行了对比分析，提出了加铺土工织物、减小水分变化梯度、采用间歇脱湿方法等提高钙质粉砂抗裂效果的手段，为岛礁工程提高地基稳定性提供参考。