An analysis of the soil mechanical properties involved in loess landslides in Heifangtai, Gansu Province

Compared with the mechanical properties of saturated loess below the groundwater table, the mechanical properties of loess in the capillary zones have different characterization parameters and testing methods. These differences have remarkable impacts on the seepage field and stability of loess slopes. Hence it is meaningful to derive accurate mechanical parameters of loess in the capillary zones. Taking the loess of Heifangtai in Gansu Province as the study area, the authors adopted both tensiometer and axial-parallel translation technique to test partial soil water content curve of loess of Heifangtai. Three empirical equations, i.e., Gardner, Van Genuchten and Fredlund and Xing, were used to fit the axial-parallel translation technique testing data to derive integrated soil water content curve and fitting parameters. Based on GDS multi-functional trixial apparatus, the authors obtained shear strength parameters of unsaturated loess via trixial shear tests by controlling matrix suction. The test results show that partial soil water content curves derived by tensiometer and axial-parallel translation technique have similar shapes, with the difference that the extensometer curve lies above that derived from axial-parallel translation technique. In the process of decrease of matrix suction from 100kPa to 20kPa, the internal friction angle decreases by about 1°, while the cohesion decreases by 22kPa. The fitted matrix suction frictional angle of Heifangtai loess is 15.6°. The tests provide parameters for unsaturated seepage and stability analysis of loess slopes in Heifangtai.