Effect of irrigation-induced densification on the post-failure behavior of loess flowslides occurring on the Heifangtai area, Gansu, China

Irrigation resulted in serious ground settlement on the Heifangtai terrace in China, and also repeatedly triggered a lot of loess flowslides on the margin of the terrace. To study the possible effect of resultant loess densification accompanying the ground settlement on the sliding behavior of these landslides, we took loess samples from the source area of a landslide in the Heifangtai terrace and performed a series of undrained ring shear tests to examine the undrained shear behaviors of these samples at differing initial void ratios. Results showed that all these tested samples exhibited purely contractive behavior throughout the entire undrained shearing process. The loose samples suffered collapse failure behavior, while those relatively denser samples experienced gradual increase in pore-water pressure after the shear failure occurred. The peak and steady-state shear strengths increased as void ratio decreased. However, the brittleness index decreased with reduction of void ratio until a certain value, after that it increased with further reduction of void ratio. Therefore, we concluded that irrigation-induced densification may have affected the occurrence and mobility of landslides occurring on the terrace margin of the Heifangtai area.