A NEW METHOD FOR THE INTERPRETATION OF THE CONSTANT-HEAD WELL PERMEAMETER

A novel semi-analytical solution for the interpretation of the constan t-head permeameter test is introduced, which accounts for the correct mixed-type boundary condition at the wellbore, unlike all published an alytical solutions. Capillarity can also be accounted for. The simplif ications are that flow from the bottom of the borehole is neglected (t herefore the solution is applicable to slender boreholes, where the pe nding depth is at least 10 times the radius) and capillarity can be mo deled with a quasi-linear approach. The Green's function approach lead s to an integral equation, the solution of which does not show signifi cant ill-posedness. Two sub-cases are presented: the first neglects ca pillary effects (the all-saturated approximation) and the second (gene ral solution) takes them into account. The all-saturated solution is s uccessfully tested against finite element simulations. The correspondi ng values of the borehole shape factor C are slightly larger than the ones obtained with approximate analytical solutions from the literatur e. When capillarity is accounted for, C changes of a factor of 10 when the dimensionless sorptive number A goes from typical values for fine soils to typical values for coarse soils (about two orders of magnitu de of variation for A). This range shifts to lower values of A as the dimensionless borehole depth increases. Consequently, the all-saturate d solution is a good approximation of the soil behavior for boreholes with large pending depth, and coarse soils. The proposed semi-analytic al solution is fast to compute and thus it is possible to use it in an automated optimization technique to fit field data and estimate the f ield-saturated hydraulic conductivity and the sorptive number; this wo uld not be feasible using a numerical solution. (C) 1998 Elsevier Scie nce B.V. All rights reserved.