考虑钙质砂细观颗粒形状影响的液体拖曳力系数试验

钙质砂作为南海岛礁填筑常用的岩土材料，其渗透性很大程度上决定着填筑后土体的固结和沉降。拖曳力系数是表达流体对土体颗粒表面力的参数，也是表征颗粒状土体渗透能力的一个重要参数，目前国内外对钙质砂拖曳力系数的研究十分有限。首先引入一个修正的三维参数 对钙质砂这种天然非规则颗粒材料的形状进行定量描述，然后开展一系列单个钙质砂颗粒在液体中沉降试验，利用高速相机记录颗粒沉降过程，结合图像处理技术获得颗粒沉降平衡速度Ut，进而计算出拖曳力系数CD和雷诺数Re，最后拟合出包含CD、Re及 三个参数的钙质砂拖曳力系数半经验模型。结果发现，在相同雷诺数条件下钙质砂的形状系数 越大，拖曳力系数越小。通过与其他研究结果对比发现，其表面微孔隙越发育，拖曳力系数越小的规律。该模型能够考虑不规则颗粒形状对拖曳力系数的影响，从而提高对土体渗透性预测的精度，对南海岛礁填筑工程中钙质砂固结和沉降的计算也具有重要意义。

Experiment on drag force coefficient of calcareous sand in liquid considering the effect of particle shape

Calcareous sand is often used as filling material in construction of artificial islands in South China Sea. The permeability of calcareous sand has significant influence on the consolidation and settlement of soil mass. The drag force coefficient, which expresses the fluid drag force on particle surface, likewise an important parameter that characterizes the permeability of calcareous sand, is not extensively studied by researchers so far. In this study, a modified three-dimensional shape coefficient is introduced to quantitatively evaluate the shape of calcareous sand. A series of single calcareous sand particle settling tests is carried out in which a high-speed camera is employed to record the settling course and imaging technique is used to obtain the terminal equilibrium settling velocity of the sand particle. By doing so, the drag force coefficient-CD and Reynolds number-Re can be determined. The experimental results show that for the same Reynolds number, the drag force coefficient increases as the shape coefficient increases. Through a comparison with other test results, it is found that the richness of particle surface pores of calcareous sand can reduce the drag force coefficient. Finally, a semi-empirical model of the drag force coefficient for calcareous sand including CD, Re and , is obtained. This model will improve the prediction of permeability of soil mass especially with particles of irregular shapes. This improvement of drag force coefficient model has the significance on the analysis of the consolidation and settlement of foundations or artificial islands filled with calcareous sand in South China Sea.