A study of the failure mode of landslide dam under the structural conditions of positive and reverse grain sequences

Landslide dam is an earth-rock dam formed by the deposits of large river-blocking landslides. Because the unique geological structure characteristics of large-scale long-runout landslides under the conditions of positive and reverse grain sequence structures differ significantly, the experimental study of the differences of failure modes and influencing factors of landslide stability of dams under these two conditions are urgently needed. In this paper, the failure process differences of landslide dams with different particle sizes and different structures are compared through indoor water tank model experiments, and the stability differences, failure mechanism and influencing factors of landslide dams with positive and reverse grain sequence structures are explored. The results show that (1) The change of failure mode of the landslide dam depends on the position where the phreatic line is exposed on the downstream slope, which has a certain delay compared with the upstream water level; (2) The failure modes of landslide dams with positive and reverse grain sequence structures depend on the relationship between slope seepage and startup critical gradient of downstream slope. (3) The location distribution of fine sand layer, the difference of startup critical gradients of fine sand layers at different depths and the difference of porosities between fine sand and medium coarse sand are the main reasons for the difference in the failures of dams with positive and reverse sequences. The research results can provide the theoretical guidance for the disaster prevention and mitigation of large landslide dams.