• Validated numerical manifold method with Monte Carlo simulations for permeability. • Relative hydraulic conductivity is near normal and governed by the largest blocks. • Representative elementary volume is about 10–15 times the maximum block size. • When rock block proportion exceeds 40%, the required volume tends toward 10 × . • Anisotropy appears only with oriented blocks; elongated ellipses amplify it. Permeability of soil-rock mixtures (SRM) is crucial for seepage analysis based on equivalent continuum theory. This study proposes a validated numerical testing procedure combining the numerical manifold method (NMM) and Monte Carlo simulations to explore rock block size and distribution effects on SRM permeability. Results show relative hydraulic conductivity ( k rs ) distribution is dominated by the largest rock blocks and follows a normal distribution. Permeability representative elementary volume (REV) is 10–15 times the maximum rock block size, converging to it when rock block proportion (RBP) > 40%. Permeability anisotropy occurs only with preferentially oriented rock blocks (principal seepage directions parallel/perpendicular to block long axis), increasing with elliptical block elongation but negligible for convex polygons (rendering SRM isotropic). The NMM-based procedure is effective, revealing key dependencies on rock block characteristics.
Li et al. (Sun,) studied this question.