Experimental study of frozen soil effect on seismic behavior of bridge pile foundations in cold regions

Ground seasonal freezing and thawing in cold regions can alter boundary conditions of bridge pile foundations and influence their seismic behaviors. This article describes a test apparatus with a custom-designed cooling system for investigating the seismic behavior of pile foundations in seasonally frozen ground. Two 1/8-scale models of a reinforced concrete bridge pier with pile foundations were fabricated for conducting quasi-static tests under unfrozen and frozen conditions. Test observations and data were used to analyze failure characteristics of pile foundation subjected to cyclic lateral loading under the two conditions and reveal the frozen soil effects. It was found that ground freezing greatly enhanced the loading carrying capacity while partly weakened the deformation capacity of the pile-soil system. It is not easy to fail if upper layer soil was frozen, and the frozen soil layer shifted the pile failure zone upward compared with the unfrozen condition. The strength degradation was obvious in the pile-soil system under frozen condition due to the fracture of the steel bar. Furthermore, the pile foundation in frozen soils exhibited more stable and reliable energy dissipation than the pile foundation in unfrozen soils under large seismic load, which was attributed to the severe damage of the pile foundation in frozen soils. A simplified force-displacement model was proposed for the pile-soil system under unfrozen and frozen conditions based on the testing results. These results can provide references for seismic design of reinforced concrete pile foundations in cold regions.