钙质砂颗粒内孔隙的结构特征分析

Microscopic characterization of intra-pore structures of calcareous sands

钙质砂是一种碳酸钙含量达50%以上的海洋生物成因的颗粒状材料。从微观结构上来看,钙质砂颗粒棱角度高、形状不规则、强度低、易破碎,且颗粒含有内孔隙。内孔隙的存在深刻影响着钙质砂的压缩、剪切和破碎等力学性能。利用激光技术对南沙群岛永暑礁环礁泻湖的未胶结钙质砂颗粒进行飞秒切割,通过光学显微镜探查并获取了颗粒的内孔隙图像,借助MATLAB图像处理软件,对钙质砂颗粒的内孔隙进行了定量分析。结果表明:较大颗粒钙质砂的内孔隙断面孔隙度相对较大,小孔隙数量较多,而大孔隙所占空间则较大;对于1 mm以上的钙质砂,缝隙状内孔隙含量远低于等轴或不等轴孔隙,等轴与不等轴内孔数量大致相等。

Calcareous sands are consisted of marine biogenic granular materials with carbonate content often greater than 50%. From the microscopic viewpoint, calcareous sand grains demonstrate highly angular and irregular in shapes and contain intra-pores. This unique intra-pore structure of calcareous sand particle is prone to crush under stress. Therefore, the calcareous sand has a relatively low strength. The intra-pore structure has a significant effect on the geotechnical properties of calcareous sands. Calcareous sand samples from the lagoon of Yongshu Reef atoll, Nansha Islands, were cut by femtosecond laser for the optical microscopic studies. The intra-pore structures were quantitatively analyzed throughout the MATLAB digital image process tool. The results indicate that, larger porosity can be found on the breakage section of larger size calcareous sand and a larger number of small pores with small total volume are in the intra-pore structure. For sand grains with a size greater than one millimeter, the number of slit shape intra-pores is far less than the number of intra-voids with equiaxed or unequal axed pores. The amount of the equiaxed and unequal axed pores are approximately the same.