Abstract: The southwestern region of China features complex geological conditions and a unique climatic environment, making stability issues of red-bed accumulation slopes unavoidable during infrastructure construction. This study focuses on the Ya'an area and investigates the dynamic response characteristics and deformation failure mechanisms of red-bed accumulation slopes subjected to seismic activity alone as well as the combined rainfall-earthquake effects through dual-model parallel shaking table tests. The research integrates multi-dimensional approaches, including macroscopic deformation analysis, moisture content and pore water pressure monitoring, and dynamic response evaluation. Results show significant differences in deformation and failure patterns between the two conditions. Under seismic action alone, deformation primarily concentrates at the slope crest, manifesting as a “seismic-initiated push-type failure”. In contrast, under combined rainfall-earthquake action, the failure zone expands to both the slope crest and toe, exhibiting a “progressive sliding failure” pattern. In terms of dynamic response, seismic action alone leads to responses concentrated at the slope crest, forming a vertical response zone, whereas under combined rainfall-earthquake action, the dynamic response extends to the upper and middle parts of the slope, propagating from the slope shoulder and surface inward. Analysis indicates that rainfall infiltration increases soil moisture content, reduces effective stress, and raises the damping ratio, which constitutes the primary mechanism for these differences. Moreover, as the number of vibrations increases, both conditions demonstrate an enhanced elevation amplification effect, with the cumulative effect at the slope crest being particularly pronounced under combined rainfall-earthquake action. This highlights the synergistic influence of rainfall and elevation as the core mechanism intensifying the dynamic response of slopes.

Key words: red bed accumulation body, shaking table test, difference of dynamic response, failure mode