Experimental Estimation of Permeability of Freeze-thawed Soils in Artificial Ground Freezing

Permeability increase of freeze-thawed soil is a well-known phenomenon. Many of researches have been conducted to clarify the mechanism of permeability of freeze-thawed soils and to estimate it with simple 1-D freeze-thaw test systems. However, it was quite doubtful whether permeability of freeze-thawed soils of AGF could be estimated directly from such a simple 1-D test.Purpose of this study is to propose an estimation procedure of permeability of freeze-thawed soil after artificial ground freezing work. Two types of experiments were conducted for this purpose. One was the 1-D freeze-thaw permeability test in which all of the freezing, loading and permeability measurements were conducted for vertical direction. The other was the horizontal displacement restrained horizontal freeze-thaw vertical permeability test (H test) in which freezing was conducted for horizontal direction while the loading and permeability measurements were for vertical. From these tests, two sets of permeability of freeze-thawed soils were obtained directly by a falling head permeability test. Moreover, water content distribution of the specimens were measured and converted into void ratio. Permeability of freeze-thawed soil of the H test was estimated based on void ratio distribution of the specimen and the relationship between permeability and void ratio from the 1-D test. Finally, the estimated and measured permeability were compared.Test results revealed that the permeability at H test can be estimated from the distribution of void ratio and that from the 1-D test, while two sets of permeability of freeze-thawed soils greatly differ from each other. It is considered that permeability increase of freeze-thawed soils is caused by deflection of void ratio distribution generated after freeze-thaw and the void ratio grows greater in the colder side and lower in the warmer side. As the result, overall permeability of freeze-thawed soils at H test became greater than that of the 1-D test.