Introduction

Laboratory tests on stratified materials usually reveal values of hydraulic conductivity that are different in the horizontal and vertical directions. This can occur in lacustrine or marine deposits, or in materials compacted in layers, such as in embankment dams. The higher conductivity tends to occur parallel to the stratification. This makes the hydraulic conductivity anisotropic; that is, the conductivity is not the same in all directions. Anisotropy at the laboratory scale is readily understandable. As illustrated in Figure 1, layering can easily extend from one side of the sample to the other. The horizontal conductivity of such a sample can be significantly higher than the vertical conductivity.