Storage Duration Effects on Soft Clay Samples

Abstract

The effects of storage duration on the sample quality of 54-mm piston samples were investigated by an extensive laboratory study. A soft clay deposit in Central Norway was used as a research site—the Tiller site. The soft clay deposit consists of two types of leached marine clay, a low-sensitivity and high-sensitivity soft clay. In total, 21 boreholes were drilled, and four samples were retrieved from each borehole between 5 m and 11 m in depth, two samples from each layer. Immediately after the sampling, the thin-walled stainless steel sampling tubes were sealed airtight and stored at the temperature of 4°C, slightly lower than the ground temperature. The storage duration varied between 0 days to 603 days, and the laboratory testing was conducted periodically, using the same equipment and test procedures. Results indicate a reduction of undrained shear strength, preconsolidation pressure, and constrained modulus with increasing storage duration. The reduction in the material properties and sample quality is rapid for the high-sensitivity soft clay, but marginal for the low-sensitivity soft clay samples. The effects of storage duration seem to be caused by physical processes taking place within the sample, as no significant changes were observed in the measurements of the water content, Atterberg limits, remolded shear strength, and pore water chemistry during the storage of the samples. In light of the laboratory results and the existing literature, an attempt has been made to explain the cause of the observed changes of the material properties and sample quality during storage of soft clay samples.