Details

Autor(en) / Beteiligte

• Xiang, J.
• Scanlon, B.R.
• Mullican, W.F.
• Chen, L.
• Goldsmith, R.S.

Titel

A multistep constant-head borehole test to determine field saturated hydraulic conductivity of layered soils

Ist Teil von

• Advances in water resources, 1997, Vol.20 (1), p.45-57

Ort / Verlag

Oxford: Elsevier Ltd

Erscheinungsjahr

1997

Quelle

Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)

Beschreibungen/Notizen

• Although most field soils are heterogeneous, existing analytical solutions to estimate field saturated hydraulic conductivity K fs in unsaturated systems assume that the soil is homogeneous. To overcome the limitations of existing analytical solutions we propose a multistep constant head borehole test to evaluate the field saturated hydraulic conductivity of layered media. The field test consists of conducting constant head borehole tests at different depths that correspond to the different layers in the soil. Measurements of water level and the stable flow rate are then used to compute the hydraulic conductivity of each layer. Equations for evaluating the saturated conductivity of each layer are derived. To determine the flow contribution of each layer, a new pressure solution is also presented. One of the assumptions of the proposed analytical solution is that the pressure gradient on the borehole wall of each layer is independent of the hydraulic conductivity of the layer. Comparison of analytical results with numerical simulation results show that this assumption is reasonable. The proposed analytical procedure can be used to calculate both the saturated and unsaturated flow components. For deep boreholes with large H a ratios (≥ 20; H constant depth of water; a borehole radius) the effect of unsaturated flow on the estimated field saturated hydraulic conductivity can be neglected and only one borehole is required. However, for shallow boreholes ( H a < 20 ), the unsaturated flow component is not negligible and can be estimated by drilling two nearby boreholes of different radii. Field test results are provided to demonstrate the application of the proposed method using deep boreholes in an arid setting. Constant-head borehole tests were repeated at different depths, depending on the number of layers in the system. This test provides a method to determine the vertical distribution of hydraulic conductivity for layered soils which is important for acçurate evaluation of subsurface flow and contaminant transport.