Reliability of using laboratory-determined soil water characteristic data for mine waste cover design

Soil water characteristic curves (SWCCs) used for the design of covers over mine wastes, are typically determined in the laboratory by performing drying tests on samples in a Tempe cell. In some cases, re-wetting is also carried out. The advantage of using drying tests is that they are carried out from the saturated state at a given sample test density; so that there is some chance of obtaining repeatable results. However, re-wetting is carried out from the arbitrary end-point of a drying test, giving a different re-wetting curve from each of these points. SWCC data may also be measured directly in the laboratory and in the field. Depending on the uniformity, stress history, structure and any cementation of soils under laboratory or field conditions, their SWCC data may be very different from the SWCC data collected after sample preparation and saturation for laboratory Tempe cell drying testing. The paper presents in situ, laboratory and field SSWC data for mine waste covers that highlight the strong influence that structure, cementation, sampling disturbance, sample preparation, saturation, uniformity, construction control and stress history can have on the data. They cast some doubt on the design of mine waste covers based solely on the use of laboratory-determined SWCCs