Abstract:Landslide dams are usually formed instantaneously by natural forces, the accumulation bodies have the characteristics of complex space structure, wide gradation of dam materials, poor dam stability, and they are easy to fail under the flow erosion. As a major natural disaster of flood and drought, safety evaluation and disaster prediction of landslide dams have been the focus of attention by the scholars around the world, but many questions remain unanswered, which are mainly manifested in: 1) Accumulation bodies are composed of natural wide-graded rockfill materials with significant state-dependent correlation, there is a lack of the state-dependent dilatancy theory and constitutive model of wide-graded rockfill materials. 2) After the formation of landslide dams, they would be affected by external loads, such as the rise of upstream water level of dammed lake, continuous unsteady seepage, landslide surge in the dammed lake, and earthquake, there is also a lack of standards and methods for stability evaluation. 3) Due to the lack of necessary flood relief facilities, the landslide dams are prone to fail; under the action of outburst flow, obvious nonlinear characteristics are manifested during the breach development, as well as strong unsteady flow characteristics of the hydraulic elements; there is a lack of numerical models for landslide dam breaching which can reflect the erosion mechanisms of wide graded materials. Therefore, it is necessary to conduct integrated scientific measures, such as field explorations, multi-scale physical model tests, and numerical simulation methods, so as to reveal the physical description, internal structure, macroscopic mechanical properties of the landslide dams and their spatial and temporal variations; and then, a state-dependent (i.e., gradation, pore ratio, and stress level) dilatancy equation for wide-graded landslide deposit will be presented, and a generalized elastic-plastic constitutive model that can adapt to complex stress paths and the limit equilibrium analysis method of landslide dam body will be established. Large-scale hydraulic model tests and centrifugal model tests of dam breaching will be conducted to reveal the dynamic erosion characteristics of landslide dam materials and the evolution law of breaches under the action of unsteady flow. Subsequently, the erosion equation of sand-laden flow under the dynamic boundary condition by the action of unsteady flow will be established, and the numerical model for dam breach process considering the fluid-solid interaction will be put forward to realize the numerical simulation of the characteristics of water flow movement, the law of dam material transport, the evolution process of breaches, and the structural instability of landslide dam in the whole process of overtopping and seepage failure. Integrating the reliability theory and numerical simulation method of dam breach process, an integrated numerical simulation platform for seepage, deformation, stability, and failure process of landslide dams considering fluid-solid will be developed; consequently, the theoretical system and method of safety evaluation and disaster prediction of the full-life cycle of the landslide dams will be established. The expected results achieved in the project will provide scientific theory and key technological support for improving the decision-making level of disaster prevention and reduction of landslide dams in China.