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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Energy is often dissipated and released in the process of rock deformation and failure. To study the energy evolution of rock discontinuities under cyclic loading and unloading, cement mortar was used as rock material and a CSS-1950 rock biaxial rheological testing machine was used to conduct graded cyclic loading and unloading tests on Barton’s standard profile line discontinuities with different joint roughness coefficients (JRCs). According to the deformation characteristics of the rock discontinuity sample, the change of internal energy is calculated and analyzed. The experimental results show that under the same cyclic stress, the samples harden with the increase in the number of cycles. With the increase of cyclic stress, the dissipated energy density of each stage gradually exceeds the elastic energy density and occupies a dominant position and increases rapidly as failure becomes imminent. In the process of increasing the shear stress step-by-step, the elastic energy ratio shows a downward trend, but the dissipated energy is contrary to it. The energy dissipation ratio can be used to characterize the internal damage of the sample under load. In the initial stage of fractional loading, the sample is in the extrusion compaction stage, and the energy dissipation ratio remains quasi-constant; then the fracture develops steadily, the damage inside the sample intensifies, and the energy dissipation ratio increases linearly (albeit at a low rate). When the energy storage limit is reached, the growth rate of energy dissipation ratio increases and changes when the stress level reaches a certain threshold. The increase of the roughness of rock discontinuity samples will improve their energy storage capacity to a certain extent.