Abstract: A series of soil water characteristic curve tests and triaxial shear tests were carried out on different structural unsaturated compacted loess samples after increasing or decreasing moisture to the same water content and dry density. The influence of different structures caused by the change of molding water content on matric suction and stress-strain characteristics as well as the structural parameter was investigated for the unsaturated compacted loess. The results indicate that the structure caused by the molding water content has a obvious effect on the soil water characteristic curve of unsaturated compacted loess. The matric suction increases with the increase of the molding water content when it is less than plastic limit. The compacted loess, which has the agglomerate structure with uniform pore size, results in relatively maximum suction at its best water content. The stress-strain curve of sample with optimum structure state is at the top of the coordinate. The degree of structural weakening is relative lighter when the water conent is less than the optimum molding water content, resulting in the stress-strain curve moves downward gradually. On contrarily, when the water conent is higher than the optimum molding water content, the degree of structural weakening is relative higher, which makes the stress-strain curve at the bottom. The proposed parameter m?r can reasonably reflect the structure of compacted loess, which overcomes the deficiency that the optimum moisture content and maximum dry density indexes cannot reflect the influence of soil structure in compacted soil engineering. The yield structural parameter m?r0 can reasonably reflect the degree of structural weakening of compacted loess with different molding water contents, and the degree of structural weakening is also reflected in the triaxial shear failure strength.

Key words: compacted loess, molding water content, structure, matric suction, stress-strain curve, structural parameter