The influences of restitution coefficient, $e_n$, interparticle friction, $\mu$, and size ratio, $R$, on gravity-driven percolation of fine particles through static beds of larger particles in the free-sifting regime ($R\gtrsim 6.5$) remain largely unexplored. Here, we use discrete element method simulations to study the fine particle percolation velocity, $v_p$, and velocity fluctuations, $v_{\mathrm{rms}}$, for $7\le R\le 50$ and a range of $e_n$ and $\mu$. Varying $e_n$ modulates the degree of particle excitation and thereby alters the nature of particle trajectories: at low $e_n$, percolation is dominated by gravity, whereas increasing $e_n$ amplifies velocity fluctuations thereby reducing the mean percolation velocity. Increasing $\mu$ decreases $v_{\mathrm{rms}}$ but its influence on $v_p$ varies with $v_{\mathrm{rms}}$, decreasing $v_p$ for low $v_{\mathrm{rms}}$ and increasing $v_p$ for high $v_{\mathrm{rms}}$. Although the influence of size ratio is weaker, larger values of $R$ increase both $v_p$ and $v_{\mathrm{rms}}$. We also assess the influence of different excitation mechanisms, specifically using static, randomly excited, and sheared beds, finding that an inverse correlation between $v_p$ and $v_{\mathrm{rms}}$ persists across all cases and is well-described by the Drude model, where increased scattering reduces mobility, when $v_{\mathrm{rms}}$ is large. However, for weakly excited particles with low $v_{\mathrm{rms}}$, the Drude analogy breaks down. In this regime, we introduce a staircase-inspired model that accounts for the gravitationally dominated percolation behavior. These findings provide fundamental insight into the mechanisms governing percolation dynamics in porous media and granular systems.

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• Granular mixing
• Granular segregation
• Dry granular materials
• Granular materials