Evaluation of sample quality from different sampling methods in Finnish soft sensitive clays

Abstract

The determination of reliable geotechnical parameters from laboratory testing is highly dependent on sample quality. Over the past decades, undisturbed sampling of soft sensitive clays has been performed using various apparatuses and procedures. This paper outlines details of the design and performance of a new Laval type tube sampler employed for the investigation of five soft clay sites located in Finland. The investigation was conducted using the new tube sampler and two different piston samplers. The sample quality is evaluated based on the recompression volume during reconsolidation to the in situ effective stress in constant-rate-of-strain (CRS) oedometer tests. Test results show that tube samples are generally characterized by higher quality, especially in low plastic clays. In particular, the quality of piston samples is highly affected by the apparatus condition and sampling operations. Furthermore, the influence of storage time on tube samples is investigated. In order to guarantee a proper confinement, and thus reducing swelling, a pressurized system is applied to the tube samples obtained in two soft clay sites. Results demonstrate that the sample quality is not significantly affected by storage time as long as the soil is properly stored into the tube.