Field-saturated hydraulic conductivity of soils from laboratory constant-head well tests

Field-saturated and unsaturated finite element analyses (FEA) of constant-head well percolation tests at three well pressure heads in two large tanks with three soils of widely differing field-saturated hydraulic conductivities (K_fs) were carried out. The results of these analyses were compared with those from the Glover classical approach. The A values in the Glover-type formula (A = K_fs/ Q_s where A was a model parameter and Q_s was the FEA steady-state infiltration rate into the soil) were shown to be independent of soil type for a particular pressure head and soil condition. Constant-head well percolation tests were carried out in two laboratory sand tanks with the same dimensional arrangement used in the finite element analyses. Field saturation was maintained by spray irrigation, and in the unsaturated condition there was no spray irrigation. Following saturation and stabilisation of the well pressure heads, drainage ports were opened instantaneously and the rate of inflow into the well was recorded. The infiltration rates, Q_s, into the sand under the two soil conditions were multiplied by the appropriate A values from the FEA for each specific pressure head to derive K_fs. A values were significantly different under field-saturated and unsaturated conditions. K_fs of the sand was also measured independently in a constant-head permeameter. Values of K_fs from the FEA and the Glover approach were in close agreement with one another, and with that measured in the constant-head permeameter. Agreement was within 13% at the higher pressure heads. The procedure appears promising for field use.