设计了专门的毛细水输盐模拟试验装置,在精确控制温度、湿度和供水水头的情况下,监测不同孔隙溶液在含盐及脱盐澄板土地仗中的毛细迁移特征。水盐迁移前后,测定模拟地仗的导热系数、孔隙半径变化,从微观角度判断外来盐分及地仗内存在的盐分对地仗盐害的贡献。试验结果表明,溶液毛细迁移速率由大到小排列为KCl与Na2SO4混合溶液>KCl溶液>Na2SO4溶液>H2O。毛细上升速度随着试样高度的增加逐渐减慢,而且脱盐澄板土中的毛细上升速率大于天然澄板土中的速率。孔隙溶液电导率随试样高度增加呈递增趋势,且天然澄板土试样的电导率普遍高于脱盐澄板土。试样的导热系数随高度的增加出现先减小后增加的总体趋势。脱盐澄板土与天然澄板土相比,孔径分布密度偏向小孔径方向;当迁移溶液为混合盐时,孔径分布较单一盐溶液时集中。模拟试验结果发现,毛细输送的外来盐分(特别是硫酸盐和氯化物复合盐)造成的土体盐胀破坏比土中既有盐分更加显著,说明控制降水入渗引起的化学淋滤作用对预防顶层洞窟壁画盐害具有重要意义。
In this study a device has been developed to simulate the capillary water and salt migration. The pore solution migration in the desalinated and pure Dengban soils can be monitored under the temperature-, humidity- and water head-controlled conditions. Before and after the capillary test, thermal conductivity and pore radius of the specimens are determined to estimate the contribution of external and internal salts to the salt damage of mural from the microscopic viewpoint. The experimental results show that solution migration rate decreases in the order of mixed KCl and Na2SO4 solution ? KCl solution ? Na2SO4 solution ? distilled water. The capillary rise rate decreases gradually with the specimen height, and the capillary rise rate in desalination Dengban soils is greater than the pure Dengban soils. The electric conductivity of soil solution increases vertically with the soil specimen height, and the conductivity of pure Dengban soil is greater than that of desalinated Dengban soil. The thermal conductivity of the soil specimens shows an overall tendency that increase first and then decrease with the rising specimen height. Compared with the pure Dengban soil, the pore-size distribution density of the desalinated Dengban soil reduces to a small aperture. In the case that the mixed salt solution is transported in soils, and pore sizes are concentrated in a more narrow area than that if single salt solution is used. It is shown that the salts transported by capillary, especially mixed sulfate and chloride, induce more severe damage than the salts contained in the soil, indicating that it is important to prevent rain water from leaching into upper caves for mural conservation.