In Situ Ground Freezing to Obtain Undisturbed Samples of Loose Sand

Abstract

In situ ground freezing with liquid nitrogen can be an excellent technique for obtaining high quality undisturbed samples from a wide range of loose sand deposits, with their in situ conditions preserved. This paper describes the techniques used during the CANLEX project to carry out in situ ground freezing and undisturbed sampling of the loose sand deposits encountered at six test sites. Specific details, with respect to the effects of difficult subsoil or ground-water conditions encountered at the sites, are provided. Modifications made to the ground freezing and sampling system to accommodate difficult ground conditions are described. The actual advance of the freezing front and the consumption of liquid nitrogen are compared with theoretical predictions. The dry coring technique utilized to recover undisturbed frozen sand samples is described. The void ratios measured for the frozen core samples are compared with void ratio measurements obtained using geophysical logging in boreholes located within a 5-m radius of the freeze pipe. The costs associated with in situ ground freezing utilizing liquid nitrogen and coring of the frozen sand at six test sites are presented.