Study on dynamic characteristics of phase change material modified loess considering seismic and freeze-thaw effects

Numerous achievements have been realized in the research of phase change materials (PCMs) to mitigate freeze-thaw (F-T) deformation of subgrade fillers in cold regions; however, the dynamic characteristics of PCM modified filler under the combined effects of earthquake and F-T cycles remain unclear. This study performed dynamic triaxial tests on plain and PCM-modified loess (PCM A and PCM B with different phase transition temperatures) after F-T cycles, and investigated the moisture content variation in the specimens' core with F-T cycles. Results showed that the dynamic friction angle was lower than the static value, while dynamic cohesion was higher. The hardening curve form remained unchanged. Plain loess had the highest dynamic friction angle and lowest dynamic cohesion. PCM modified loess had reduced dynamic friction angle due to weakened particle friction, but increased dynamic cohesion from finer PCM particles. After three F-T cycles, dynamic friction angle and dynamic cohesion stabilized. Both initial shear modulus and the maximum shear strength decreased with F-T cycles and were highest in plain loess, followed by PCM B and PCM A modified soil. Ignoring the moisture loss, the differences in moisture contents between the core and shell sections revealed the evolution of dynamic characteristics with F-T cycles and PCM types. Grey absolute relational degree analysis indicated the F-T effect on dynamic friction angle was stronger than PCM type. The study recommends using dynamic strength indices after three F-T cycles for Coulomb strength envelope in seismic cold regions. • Considering freeze-thaw (F-T) and seismic effects, the dynamic characteristics of plain loess and PCM modified loess were examined via dynamic triaxial test. • The hydrothermal state and the gradation of plain loess and PCM modified loess were determined to explain the dynamic characteristics in F-T cycles. • The relational analysis reveals that the F-T effect has a greater adverse impact on the dynamic friction angle than the PCM type.