Experimental study on the freezing-thawing behavior of compacted earth

Most of compacted earthen constructions are located at temporary and seasonal frozen areas, consequently exposed to repeated freezing-thawing (F-T) environment induced by significant temperature fluctuations. The F-T cycles can cause severe damage to the compacted earthen materials and reduce the structure’s durability. In this paper, a series F-T tests were performed in order to study the damage mechanism of the compacted earthen materials subjected to F-T cycles. The experiments were carried out under two confining pressures (σc= 0 kPa and 50 kPa) and three freezing temperatures (TF=−5℃, −8℃ and −13℃), with a thawing temperature of TT= 9℃. Evolution of elastic moduli and accumulation of irreversible strain at the end of each F-T processes were analyzed through cyclic loading–unloading tests under undrained condition. Results indicate that each F-T cycle could be characterized by main six stages, whose physical meaning has been explained through a thermodynamic approach. With increasing number of F-T cycles, a growth of the Young’s modulus was observed when the material was in a frozen state, and the opposite was found for the thawed state. This may be explained by an increase in macro-porosity as F-T cycles progress, which would be in line with the accumulation of residual deformation and the increase of freezing and thawing temperatures. The applied confining pressure was eventually found to provide a positive resistance against permanent deformation. This discovery can provide experimental support to the safety design of earthen wall situated in cold regions.