钙质砂中毛细水高度与影响因素试验研究

Experimental study on capillary rise and influencing factors in calcareous sand

钙质砂是指富含碳酸钙或其他难溶碳酸盐类的海洋成因的特殊介质,具有形状不规则、多孔隙且富含内孔隙等特点;土体因孔隙特性而存在广泛的毛细现象,植物根茎内的导管有如极细的毛细管,能由此吸收土壤里的水分,故钙质砂地层毛细水上升高度研究对岛礁生态研究有重要的意义。采用竖管法研究级配、粒径、干密度、盐度等因素对钙质砂毛细水上升高度的影响,结果显示:细颗粒含量越多、级配越好的连续级配钙质砂试样毛细水上升高度越高;单一粒径钙质砂试样毛细水上升高度随粒径的增大而减小;随着钙质砂干密度增加,粒径小于0.075 mm时毛细水上升高度逐渐减小,而粒径为0.075~0.250 mm时毛细水上升高度逐渐增大;与淡水相比,在低盐度下NaCl溶液对毛细水上升有抑制作用,海水对毛细水上升有促进但效果微弱。钙质砂中毛细水上升高度随时间变化关系符合双对数坐标下的二次多项式关系,其参量与钙质砂的物理性质以及溶液类型相关。

Calcareous sand is a special medium with high calcium carbonate content or other insoluble carbonates, and has characteristics of irregular shape, porous and rich in inner pores. Capillary rise is a universal phenomenon in soil due to the pores. The tube inside rhizome is like a very fine plant capillary, which can absorb water from the soil. Therefore, the study on height of capillary rise in the calcareous sand has great significance to the ecological construction of the reef island. In this paper, the vertical tube tests are carried out to study the influence of gradation, particle size, dry density and salinity on the capillary rise in calcareous sand. Results show that the finer the particles and better gradation, the higher capillary water rise in the continuous graded calcareous sand. The height of capillary water rise decreases with increasing particle size in the single-sized calcareous sand. The capillary water rise decreases when the particle size is less than 0.075 mm with increasing dry density of the single-sized calcareous sand, while the height gradually increases with the particle size of 0.075-0.250 mm. Compared with fresh water, the NaCl solution inhibits the capillary water rise at low salinity, and the seawater promotes the capillary water rise but only weakly. The relationship between the height of capillary rise and time in calcareous sand fits well with the quadratic polynomial relationship in double logarithmic coordinates, and the physical properties of calcareous sand and the solution type are related to the parameters.