The permeability of natural soft clays. Part I: Methods of laboratory measurement

Abstract

The methods of measuring the permeability of clays in the laboratory are investigated. Constant head tests in the triaxial are best suited for testing large specimen under field stress conditions provided the cell is modified to eliminate leakage. Using this type of test, the validity of Darcy's law is confirmed.Falling head tests in the oedometer are very simple to perform and subject to minimal sources of errors. However, small size specimens may not be totally representative.Indirect evaluations of the permeability from consolidation tests are shown to be unreliable particularly in structured natural clays: evaluation of k from c v measurements in step-loaded tests gives much too low values, constant rate of strain tests strongly overestimate k in the vicinity of σ p ′ and give nonrepresentative e vs. lg k relations; controlled gradient tests tend to underestimate k at all void ratios. Keywords: permeability, clays, laboratory tests, test equipment, consolidation tests.