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 d epth greater than 10 m in Canada. Once frozen, the sand was cored and brought to the surface using a Cold Regions Research and Engineering L aboratory core barrel, which is used extensively in permafrost regions . The design, installation, and performance of the liquid nitrogen fre ezing systems are described in detail. The drilling, sampling, and pre paration of the frozen core for transport to the testing facility are also outlined. The quality of the core retrieved during the sampling w as judged to be excellent, and good agreement was found between the vo id ratios measured using both the frozen core and high-quality gamma-g amma density logging techniques, which were performed adjacent to grou nd-freezing and sampling locations.