Hydraulic Properties of Disturbed and Undisturbed Soils

A study was made to determine whether or not disturbed materials are suitable for modeling undisturbed porous media. One requirement for similitude between a model and prototype involving partially saturated flow is that the relationship between permeability and capillary pressure be similar. In the case of disturbed media, the relationship is usually represented by a straight line on a log-log plot for capillary pressures greater than the bubbling pressure. The requirement for similitude of media is satisfied if the slope is the same, provided the model is scaled in relation to the magnitude of the bubbling pressure. Apparently, a medium obtained by pulverizing the material at the site of the prototype usually would not be suitable for a model. Suitable disturbed materials are available, however, for modeling the undisturbed media studied to date. The relationship between permeability and capillary pressure for structured soils may not be adequately described by slopes of the function on a log-log plot alone. Further study is needed to determine the role of sample boundary effects for such materials. Unconsolidated sands usually are not suitable media for modeling structured soils, the pores of sands being more uniform in size.