How is seepage controlled in earth dams?

Seepage control in earth dams through: (1) Core - central impervious zone (clay) to minimize flow through dam, (2) Cutoff - extending impervious layer into foundation (trench, sheet pile, grout curtain), (3) Upstream blanket - extends impervious zone to increase seepage path, (4) Horizontal drain/filter - collects seepage water safely without piping, (5) Relief wells - reduce uplift pressure in foundation. Filters designed with gradation criteria preventing particle migration (D15 filter/D85 base < 4-5). Exit gradients must be below critical to prevent piping failure.