Experimental investigation on the characteristics of seepage failure of landslide dams with strongly permeable zones

Abstract Landslide dams are formed by river blockages caused by landslides or other slope instability bodies. They exhibit loose structure, poor stability and strong permeability. Large water head caused by water-level increase can trigger seepage deformation of soil and influence the stability of landslide dams, possibly leading to dam breach and catastrophic damage. Various landslide dam structures also result in differences in seepage characteristics. In this study, multiple physical model tests for seepage failure of landslide dams with strongly permeable zones were designed. The influence of the location and gradation of the strongly permeable zones on the seepage of landslide dams was studied. The characteristics and modes of seepage failure of landslide dams with strongly permeable zones were analysed. The experimental results showed that the cyclic evolution failure of piping and downstream slope collapse was an essential failure mode for the seepage-induced failure of landslide dams with strongly permeable zones. Compared with the strongly permeable zone at the bottom of a landslide dam, the piping caused by seepage evidently promoted the slope erosion of the dam with the strongly permeable zone in the middle. As the permeability coefficient of strongly permeable zones increased, piping was faster and easier to form, and piping failure, slope erosion, and slope collapse were more severe. The seepage failure of landslide dams mainly included the emergence of seepage water, piping, slope erosion, and downstream slope collapse. Piping was caused by the erosion and migration of some fine particles of soil in seepage channels in the dam. When the flow drag force could overcome the resistance force among the soil particles, some fine particles and even large particles on the downstream slope surface were continuously eroded. This study provides new insights into the evolution process and breach mechanisms for the seepage-induced failure of landslide dams with strongly permeable zones.