How is soil permeability determined and why is it important?

Permeability (hydraulic conductivity) is measured by: constant head test for coarse-grained soils (k = QL/Aht), falling head test for fine-grained soils (k = aL/At * ln(h1/h2)), and field tests (pumping tests, slug tests). Typical values: gravel 10^-1 to 10^-2 m/s, sand 10^-3 to 10^-5 m/s, clay 10^-9 to 10^-11 m/s. Permeability affects seepage quantity, pore pressure distribution, consolidation rate, dewatering design, and contaminant transport.