Objective During long-term service, debris-flow protection structures are frequently subjected to coupled damage from impact, abrasion, and environmental factors. Their failure forms are complex and show significant spatial heterogeneity and time-dependent accumulation. To systematically reveal their failure mechanisms,

Methods this study mainly relies on field investigations of typical debris-flow protection projects in Sichuan Province from 2022 to 2025. Digital imaging was used to record macroscopic morphology and surface features. Ion chromatography and inductively coupled plasma emission spectrometry were used to quantitatively analyze water-soluble ions in the surrounding environment. Ultrasonic nondestructive testing and scanning electron microscopy (SEM) were also used to characterize internal damage and microscopic morphology.

Results The failure modes and damage-evolution patterns of protection structures under debris-flow action were comprehensively analyzed. The results show that debris-flow action on engineering structures mainly includes impact, abrasion, and immersion. The corresponding failure modes can be classified as overall instability, local component failure, foundation failure, interface debonding, abrasion damage, and scour-induced undermining. Abrasion damage and interface deterioration show significant cumulative effects over time and are coupled with impact and seepage, becoming key drivers of performance degradation in protection structures. From the perspective of damage evolution, structural materials undergo a typical three-stage process of initial microdamage, crack propagation, and macroscopic failure. Internal damage is characterized by multiscale features such as cracking in the interfacial transition zone (ITZ), increased pore connectivity, and aggregate failure.

Conclusions The results provide a theoretical basis for performance assessment, service-life prediction, and abrasion-resistant design of debris-flow protection structures.