A vacuum permeability test for compacted clay

Abstract

A vacuum permeability test utilizing high hydraulic gradients has been devised for compacted clay of low permeability. The test induces easily measurable flow rates in virtually impervious soils by placing a vacuum at the drainage end of the sample and an elevation head at the inflow end. The apparatus used in the test could easily be constructed with materials commonly available in laboratories for routine soil tests. The sample can either be compacted in the permeameter (a glass cylinder) or can be seated in sand and sealed with an asphalt bond.

The anticipated difficulties, capillary effects, undetected leakage, and permeability reduction by entrapped air, do not introduce appreciable error as shown by the linearity of flow velocity-hydraulic gradient curves and the general agreement of test results with those obtained from a falling bead, non-vacuum test.

Relative coefficients of permeability can be obtained within a few days after the start of the test. It is concluded that this rapid, inexpensive method gives adequate values of coefficient of permeability for most experimental work on compacted clays.