Disturbance of sand samples obtained by piston samplers and ground freezing

Abstract

High quality sampling of sand and silty sands is extremely challenging. Undisturbed samples of sand can be obtained by means of very expensive and time-consuming techniques such as ground freezing. Given the high costs and expertise required to obtain undisturbed sand samples through ground freezing, piston sampling techniques are usually used in engineering practice. This paper summarises the experiences, technical difficulties, disturbance analyses and issues encountered during sand sampling at the Norwegian Research Site at Øysand using piston sampling and ground freezing technology. Two state-of-the-art piston samplers were used (NGI-Geonor composite piston sampler and Geonor K-200 thin-wall push piston sampler) along with the state-of-the-art Japanese gel push piston sampler. Ground freezing was successfully achieved also both on sands and silty sands at Øysand. Sample disturbance was assessed qualitatively and quantitatively through analysis of micro-computed tomography images. Results from these analyses provide an overview of the strengths and weaknesses of the three piston samplers in comparison with ground freezing, together with recommendations for sampling of sands using piston techniques.