Pile eigenfrequency shift caused by soil unfreezing

Pile foundations are commonly used in buildings located on seasonally freezing soils, where freezing and thawing can distort foundations and damage structures, necessitating monitoring with various sensors. We focused on how seasonal temperature changes, particularly soil thawing and freezing, affect the mechanical properties of soil and, consequently, the strain in piles. We conducted an experiment that recorded the background vibration of a single pile with a weight over several weeks. The pile was buried in frozen soil during winter and left in natural conditions until the soil thawed completely. Periodic vibration measurements revealed a significant decrease in the eigenfrequencies of the pile (10–20%) during thawing, reflecting a reduction in the stiffness of the pile-soil system (20–40%). These findings highlight the impact of soil freezing and thawing on the dynamic properties of pile foundations, offering insights for monitoring and mitigating structural deformation.