<p>Rock-avalanche dams are among the most common and hazardous types of natural dams, characterized by distinct internal heterogeneous structural characteristics. However, research on the breach process of rock-avalanche dams remains in its early stage, with limited focus on the role of the coarse carapace layer. This knowledge gap hinders the accurate assessment of rock-avalanche dam breach risks. This study conducted flume experiments to investigate the breach evolution process of rock-avalanche dams, using a generalizability model incorporating an upper coarse carapace layer. The differences in breach processes between homogeneous and rock-avalanche dams with upper coarse carapace layer were systematically analyzed. Additionally, the effects of carapace thickness and inflow discharges on the dam breach were examined. Furthermore, a longitudinal breach pattern for rock-avalanche dams with upper coarse carapace layer was proposed. The results reveal that the surface carapace of rock-avalanche dams can delay the occurrence of overflow while accelerating the breach process, ultimately amplifying the peak outburst discharge. Compared to homogeneous dams, rock-avalanche dams with upper coarse carapace layer exhibit distinct multi-stage scarp during the initiation stage. The hydraulic jump phenomenon at the carapace-body interface results in a carapace reverse tilt and a body erosion platform at the breach bottom. Additionally, the hydraulic jump and reduced sediment-carrying capacity of the outburst flow lead to a gradual increase in erosion resistance from upstream to downstream. The longitudinal breach pattern of rock-avalanche dam with upper coarse carapace layer consists of three processes: plane erosion, spindle erosion, and multi-section erosion. This study provides a valuable reference for analyzing the breach processes of rock-avalanche dams with upper coarse carapace layer characteristics and offers decision support for disaster risk assessment and emergency rescue to geo-disasters.</p>