各向均等压缩条件下原状黄土的吸力特征

Soil-water Characteristics of Undisturbed Loess under Isotropic Compression Condition

采用非饱和土三轴仪,对不同含水率西安原状黄土进行常含水率各向均等压缩试验,最大净围压为400 kPa。用轴平移技术量测了无和有净围压条件下黄土的基质吸力。分析常含水率各向均等压缩过程中净围压变化对基质吸力的影响及其变化规律,提出原状黄土土水特征曲线的表达式。研究结果表明:含水率一定时,净围压变化对基质吸力的影响与含水率有关。含水率小于缩限及大于缩限时,基质吸力随净围压的增大呈现出不同的变化趋势;含水率在缩限与塑限之间变化时,净围压对基质吸力的影响较大,含水率小于缩限或大于塑限时,其影响很小。含水率小于缩限时,在净围压变化及含水率变化条件下所对应的二类基质吸力与饱和度关系具有不同的变化趋势;净围压相关的饱和度变化比含水率相关的饱和度变化对基质吸力的影响要小得多。净围压对饱和度与基质吸力关系的影响比较大。净围压(≤400kPa)对含水率与基质吸力关系的影响可以忽略,用无应力条件下呈对数函数的含水率与基质吸力关系来描述原状黄土的土水特征。

Using triaxial apparatus for unsaturated soils,the isotropic compression tests at constant water content are conducted on undisturbed loess in Xi'an under different water contents. The maximum of net confining pressure is400 kPa. Matric suction is measured by an elevated all round air pressure and with measured pore-water pressure under zero and applied stress. Influences of net confining pressure on matric suction characteristics of undisturbed loess are determined and illustrated during isotropic compression at constant water content. The formula of soil-water characteristics of undisturbed loess is obtained to determine the matric suction under zero-applied stress. Experimental results show that the influence of net confining pressure on matrix suction is related to water content. When water content is smaller than shrinkage limit,the relationship between matrix suction and net confining pressures is different from that larger than shrinkage limit. The influence of net confining pressure is large when water content is between shrinkage limit and plastic limit,and it is slight when water content is smaller than shrinkage limit or larger than plastic limit. The relation between matric suction and degree of saturation related to net confining pressure with water content smaller than shrinkage limit is different from that related to water content. The influence of degree of saturation related to net confining pressure on matric suction is much smaller than that related to water content. Net confining pressure has relatively large influence on the relation between degree of saturation and matric suction. When net confining pressure is smaller than 400kPa,its influence on the relation between water content and matric suction is negligible,and the soil-water characteristics of undisturbed loess is illustrated by the logarithm function relation between water content and matric suction under zero-applied stress.