Pile-forest dams are vertically structured lattice dams based on piles, which offer favorable load-bearing conditions, relative material efficiency, and the ability to trap coarse sediment while allowing fine sediment to pass through. Existing research on pile-forest dams has mainly focused on constructing different layout models to investigate the impact loads, sediment source interception, and regulation of debris flow performance. This study takes Yangjiagou as an example and conducts field surveys and numerical simulation calculations using FLOW-3D software to explore the erosion patterns of pile-forest dam foundations under different influencing factors. Various layouts (single-row piles, double-row piles, pile spacing, and row spacing) of pile-forest dam models were established. The research findings indicate that: (1) In the overall design of pile-forest dams, the pile arrangement should not be too dense, and the recommended pile spacing and row spacing are 2.5 meters; (2) Single-row piles exhibit weaker stability and are prone to shear failure under debris flow impact. They have a lesser "sediment source stabilization" effect on the upstream area compared to multiple-row piles, but the scouring depth and erosion scale of single-row piles are smaller than those of multiple-row piles. The research outcomes provide data support for the layout patterns and erosion mechanisms of pile-forest dams, offering valuable insights for the design of post-earthquake debris flow prevention and control projects.