Ground freezing and sampling of foundation soils at Duncan Dam

In situ ground freezing to obtain undisturbed samples of a loose sand beneath the Duncan Dam in British Columbia is described. This was the first known use of ground freezing to assist in obtaining samples at depth greater than 10 m in Canada. Once frozen, the sand was cored and brought to the surface using a Cold Regions Research and Engineering Laboratory core barrel, which is used extensively in permafrost regions. The design, installation, and performance of the liquid nitrogen freezing systems are described in detail. The drilling, sampling, and preparation of the frozen core for transport to the testing facility are also outlined. The quality of the core retrieved during the sampling was judged to be excellent, and good agreement was found between the void ratios measured using both the frozen core and high-quality gamma–gamma density logging techniques, which were performed adjacent to ground-freezing and sampling locations. Key words : ground freezing, cohesionless soils, undisturbed sampling.