Modification of triaxial apparatus for permeability measurement of unsaturated soils

Both the shear strength and the permeability of unsaturated soils are important engineering properties that are required in numerous geotechnical designs. Many studies on the shear strength of unsaturated soils have been reported; however, only a limited number of studies on the permeability of unsaturated soils have been presented. This might be due to the fact that the time and the costs associated with unsaturated permeability measurements are excessive. The purpose of this paper is to introduce the modification of a triaxial apparatus for the direct measurement of permeability in conjunction with shear strength tests on unsaturated soils under multiple cycles of drying and wetting. Detailed designs and modifications are carried out to allow the unsaturated permeability and the shear strength of a soil to be measured for the same soil specimen. The test results are found to be more consistent as both measurements are conducted on the same specimen. A series of unsaturated permeability tests and then a series of unsaturated consolidated drained (CD) triaxial tests, under multiple cycles of drying and wetting, are conducted on three different soils, and the results are shown to be compatible with the theory reported in literature.