Abstract:

The dynamic torsional shear triaxial tests are carried out on loesses of Lanzhou, Luochuan and Yangling under different water contents and different stress states; and then the dynamic shear stress-strain curves of loesses are obtained. Besides, according to Hardin-Drnevich hyperbolic model, the soil structural quantitative parameters, which are based on the dynamic shear stress, are developed; and the dynamic structural characteristics of unsaturated loesses in Lanzhou, Luochuan and Yangling are analyzed by using the parameters. Results show that the structural parameters of Lanzhou, Luochuan and Yangling loesses firstly reduce along with the increase of the dynamic shear strain; and then remain at a stable level; water content and consolidation stress have significant influence on the structural parameters. Under the same consolidation stress condition, the lower water content, the greater dynamic structural parameters of the loess; and under the same water content, the smaller consolidation stress, the greater dynamic structural parameters of the loess. In conclusion, under the same condition, the dynamic structural characteristics of Yangling loess is the strongest; the following is Luochuan loess; and Lanzhou loess is the weakest; in other words, the structural characteristics of loesses in the geographical spatial distribution exists a law of increment from the northwest to the southeast.

Key words: unsaturated loess, dynamic torsional shear test, dynamic structural characteristics, structural parameters, district comparison