Background Barrier dams, formed by natural forces and accumulated loosely, are highly susceptible to breaching, posing a serious threat to life and property safety. At present, researchers pay more attention to the impact of the overall material composition of landslide barrier dam on the dam breaching and stability, and do not consider the internal distribution characteristics of the materials. Is there any influence of the distribution of material composition on the breaching and stability of landslide barrier dams?

Methods According to previous studies, four types of landslide barrier dams were established considering the different distribution characteristics of the material, which are uniformly mixed type (UM), top-coarse and bottom-fine type (TCBF), pre-coarse and post-fine dam (PCPF) as well as pre-fine and post-coarse type (PFPC). Through model tests, the whole breaching process was recorded, and the characteristics of the breaching development and the outflow discharge were analyzed.

Results 1) Different barrier dams shared similar four breaking process, that is, seepage erosion stage, retrograde erosion stage, breach development stage and coarsening equilibrium stage, but obvious characteristics in different stages have been observed for different barrier dams.2) The duration of the seepage erosion stage of the PCPF-type dam is the shortest while the UCBF-type dam is the longest, and the latter is 2.5 times of the former. 3) The overtopping failure process of UM-type dam and TCBF-type dam are earlier than that of PCPF-type dam and PFPC-type dam. The erosion rate of the UM-type dam is the smallest, and the breach development process is relatively uniform.The erosion groove of the PFPC-type dam was narrow and deep developed in the retrograde erosionstage, and local collapses of the slope bank occurred most frequently during the breach development stage, causing the highest erosion rate during the first 10 s of the breach development stage and leading to frequent collapse-clogging-breaking phenomenon. A wide and shallow erosion groove developed during the retrograde erosion stage in the PCPF-type dam. The erosion rate is the largest during the later breach development stage, and the local area of the downstream slope is prone to sliding.4) The amplification coefficients of the outburst-flow peak discharge also vary among different landslide barrier dams, sharing an order of PCPF < TCBF < UM < PFPC, reaching a value of 4.24, 4.83, 5.03 and 5.38 respectively.

Conclusions The results demonstrate that the distribution characteristics of the material composition inside a landslide barrier dam have different effects on the breach time, breach process and breach flow discharge of the dam, which should be considered in the stability analysis of landslide barrier dam.