Preservation and storage of geological samples : implications and suggested methods

This report describes a study undertaken to determine the effectiveness of various preservation methods for reducing desaturation of geological samples held in long-term storage. A total of 24 samples of Callovo-Oxfordian claystone were tested using different storage methods. The change in water content was recorded regularly over one year and revealed that the best method is using a chamber vacuum sealer with sandwiched aluminium/mylar bags. Oven-drying two samples also revealed that it can take up to 7 days for all water to be removed from samples, so this should be the minimum drying time before geotechnical properties are determined. The moisture loss seen in a pre-compacted sample of bentonite showed that exposure to the atmosphere of just 1 hour is sufficient to reduce saturation sufficiently to change THMCG properties. Therefore, samples should be vacuum sealed in Mylar as much as possible during sample preparation.