Percolation testing and hydraulic conductivity of soils for percolation areas

The results of specific percolation tests are expressed in terms of field s aturated hydraulic conductivity (K-fs) of the soil. The specific tests comp rise the Irish SR 6 and the UK BS 6297 standard tests and the inversed auge r hole and square hole tests employed for the design of land drainage. Perc olation times from these tests are converted to K-fs values using unit grad ient theory and the Elrick and Reynolds (Soil Sci. 142(5) (1986) 308) model which takes into account gravitational, pressure head and matric potential gradients. K-fs is then expressed as the inverse of the percolation rate t imes a constants in this way the percolation rate can be directly related t o K-fs of the soil. A plot of K-fs against percolation rate for the Irish S R 6 and the UK BS 6297 standard tests is asymptotic at K-fs values less tha n 0.2 in, d and greater than 0.8 m/d. This behaviour creates difficulty in setting limits for percolation rates in standards. Curves are provided whic h enable K-fs values to be read oil from percolation tests without the rest rictions of head range currently enforced, for example in the Irish SR 6 an d BS 6297 standards. Experimental measurements of percolation rates and K-f s were carried out on two sands in the laboratory and in the field on two s oils. K-fs of these four materials was also measured using a tension infilt rometer and the Guelph permeameter. The saturated hydraulic conductivities (K-s) of the sands were also estimated in a Calling head laboratory apparat us and by the Hazen formula. There was good agreement between the different tests for K-fs on each material. Because percolation time continued to inc rease significantly in consecutive tests in the same test hole while K-fs b ecame constant, the latter is a better measure of the suitability of soils for percolation. (C) 2001 Elsevier Science Ltd. All rights reserved.