Behavior of geosynthetic-encased stone column reinforced foundation under freeze-thaw cycles

In this paper, an experiment study was carried out to identify the fundamental behavior of geosynthetic-encased stone column (GESC) reinforced foundation under freeze-thaw cycles. Three loading tests under four freeze-thaw cycles were considered. A 10-m thick reinforced foundation unit consisted of four floating GESCs with 2.5-m underlain clay layer, and the foundations were preconsolidated to three different initial degrees of consolidation (U = 1.0, 0.6 and 0.3, respectively). The results showed that soil near GESCs had a larger frozen depth due to the excellent heat transfer ability of GESCs. An extra uneven subsidence of soil also appeared around GESCs. Voids could be found between foundation soil and the loading plate after thawing, which indicated that only GESCs carried the overburden pressure. The GESCs showed outward bending under lower initial degree of consolidation, while inward bending under higher one. A bulging failure was observed on frozen part of GESCs, especially at the connection of encasement in foundation with lower initial degree of consolidation. In the first freezing process, a rapid decrease in frost heave force was noticed, inferring the fracture of frozen soil. The stress on GESC was found to almost have no change until complete freezing, when the soil was freezing and the stress on soil exceeded that on GESC. Negative pore pressure was observed in the foundation soil, and the absolute value decreased with the increasing overburden pressure. Both the peak positive and negative pore pressures were reduced as the foundation was preconsolidated to a higher degree. The freeze-thaw cycles were also found to generate excess pore pressure in soil during thawing. Moisture migration was also analyzed using Electrical Resistivity Tomography (ERT) method, and the results showed that moisture tended to go upwards and outside the reinforced unit from thawing to freezing, while downwards and inside the unit from freezing to thawing.