Soil Permeability Test

The soil permeability test determines the coefficient of permeability k (m/s), the rate at which water flows through soil under a unit hydraulic gradient. IS 2720 Part 17 covers the laboratory methods — the constant-head test for coarse, free-draining soils (sands, gravels; k > 10⁻⁴ m/s) and the falling-head test for fine soils (silts, clays; low k). Field methods (pumping/borehole tests) give the in-situ mass permeability for designs that need it.

k spans roughly 10⁻² m/s for clean gravel down to 10⁻⁹ m/s for clay. It governs seepage through dams and cofferdams, dewatering well/sump design, the rate of consolidation, drainage-layer and filter design, and the suitability of clay liners + cores. Mis-estimating k by an order of magnitude routinely under-sizes dewatering systems on deep excavations.