Abstract: The hydraulic characteristics of compacted loess are controlled by its microstructure, which depends on the sample preparation conditions. This study aims to explore the influence of sample preparation conditions on microstructure, saturated permeability coefficient and soil-water characteristic curve (SWCC) of compacted loess. The mercury intrusion porosimetry (MIP) tests, variable head tests and SWCC tests were carried out on the specimens prepared under different conditions to obtain the pore-size distribution curves, saturated permeability coefficients and their variations with the seepage times, and SWCCs. The results show that: (1) The molding water content affects the density of mesopores (2 000 nm < d ≤ 12 000 nm) and that of micropores (150 nm < d ≤ 2 000 nm) by affecting the sizes of aggregates; the higher the molding water content of the specimen is, the smaller the density of mesopores is, and the larger the density of micropores is. The compaction degree has a significant effect on the density of mesopores by affecting the arrangement of aggregates; the greater the compaction degree is, the tighter the arrangement of aggregates is, and the smaller the mesopores content is. (2) The initial saturated permeability coefficient reduces with the increases of compaction degree and molding water content of compacted loess. When the compaction degree is small (85%), the saturated permeability coefficient of compacted loess decreases with the increase in number of seepage, and it rises with increasing number of seepage when the compaction degree is high (90% and 94%). (3) The molding water content mainly affects air entrance vaule (AEV) and the slope of the transition zone. The greater the molding water content is, the smaller the AEV is, and the slope of the transition zone is. Compaction degree mainly affects AEV and saturated moisture of specimens. The higher the compaction degree is, the higher the AEV is, and the smaller the saturated water content is.

Key words: compacted loess, compaction degree, molding water content, pore-size distribution curve, saturated permeability coefficient, soil-water characteristic curve