ISO 17312:2005 specifies the determination of the hydraulic conductivity of granular soils (e.g. sand and gravel) using a constant-head method involving a rigid-wall permeameter to measure the laminar flow of water. The procedure establishes representative values of the hydraulic conductivity of granular soils that can occur in natural deposits as placed in embankments, or when used as base courses under pavements. In order to limit consolidation influences during testing, this procedure is applicable only to disturbed granular soils containing not more than 10 % soil passing a 75-micrometre sieve. ISO 17312:2005 is applicable to the measurement of hydraulic conductivity of compacted samples of sands and gravels containing little or no silt, where flow along the rigid wall of the permeameter has no practical implications on the test results. ISO 17312:2005 is not applicable to silt and clay, where seepage/flow at the boundaries is not acceptable.