Effect of Ground Freezing with Liquid Nitrogen on Freezing Rate and Mechanical Properties of Coastal Clayey Silt: Fid-Bau Portal

Effect of Ground Freezing with Liquid Nitrogen on Freezing Rate and Mechanical Properties of Coastal Clayey Silt

Choi, Hyun-Jun / Won, Jongmuk / Lee, Dongseop / Lee, Hyobum / Choi, Hangseok

The artificial ground freezing (AGF) method is an environmentally friendly ground improvement technique for numerous geotechnical applications. It can be used in fine-grained soils, which may not be efficiently improved via conventional cement-based ground improvement techniques. However, some of the issues hindering the application of the AGF method to fine-grained soils include inefficiency in achieving the target volume of frozen soil and degradation in mechanical properties of the soil after the freezing-thawing process. In this paper, the freezing rate and degradation in strength and stiffness of a clayey silt in South Korea were investigated using field experiments. At two different outlet temperatures ( $- 180 ° C$ and $- 120 ° C$ ), liquid nitrogen was injected into the freezing pipe to evaluate the freezing rate. A simple equation to estimate the theoretical radial freezing rate was proposed and compared with the experimental results. In addition, a piezocone penetration test (CPTu) and pressuremeter test (PMT) were performed to assess the degradation in strength and stiffness of the soil after the freezing-thawing process. Results of the CPTu, PMT, and laboratory experiments revealed that the degradation in mechanical properties of Korean clayey silt could be attributed to the rearrangement of soil particles.