Stability of landslide dam is of great concern worldwide. Geomaterials of a landslide dam, a natural dam, are usually at unsaturated state, which requires a saturated/unsaturated constitutive model to describe the hydro-mechanical behavior of the landslide dam materials (LDM). Study (Xiong et al., 2018) has been done on the failure mechanism under seepage loadings both in model tests and numerical simulations, while the element behavior of LDM is still unclear. In this paper, large-scale saturated triaxial compression tests under undrained condition, water retention test and unsaturated triaxial compression test under undrained/unvented condition were conducted on four kinds of LDM. Results of saturated large-scale triaxial tests show the shear stress ratio at critical state with a gap-graded mixture is the largest, which indicates the landslide dam made of this material is the most stable. Water retention curve (WRC) of LDM is obtained in water retention tests. Hysteresis of WRC varies with different grain size distributions. Unsaturated triaxial test results in four different LDM show that the strength of the materials increases with the increase of suction and mean net stress, and the same tendency in the change of the volumetric strain can be observed.

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