Effects of tube sampling in soft clay: a microstructural insight

This paper analyses the effects of tube sampling in soft clay with particular emphasis on the modifications that occur in the clay fabric for tube specimens retrieved using open samplers (Shelby) as well as a fixed-piston sampler. Tube specimens of an estuarine soft clay retrieved from the National Soft Soil Testing Facility located at Ballina in northern New South Wales (Australia) are analysed in this study. Mercury intrusion porosimetry tests are carried out to infer the pore size density function of specimens trimmed at different locations along the tube and these are compared against those performed on undisturbed clay, obtained from Sherbrooke specimens, to estimate variations in the natural soil fabric due to tube sampling. It is shown that tube sampling induces important modifications in the natural pore size distribution (PSD) of the clay, not only at the perimeter but also at the centreline of the sampler. This phenomenon is more pronounced at the top and bottom ends of the sampler and increases with a decrease in the sampler diameter. The use of the large-diameter fixed-piston sampler reduces dramatically the variations in both the micro and macro void ratios during tube sampling.