A new approach for improving lateral performance of pile foundations in seasonally frozen regions

Ground freezing in cold areas can cause brittle damage to deep foundations during seismic loading. This paper presents a novel solution to this problem by replacing local soil around the pile with a temperature-insensitive composite material, namely polyurethane glue-bonded rubber particles-sand mixture (PolyBRUS). Three 1/12 scale reinforced concrete pile foundations embedded in unfrozen, frozen, and frozen with local replacement conditions were prepared, and quasi-static cyclic loading tests were conducted to reveal the adverse effects of seasonal freezing on pile foundations and verify the performance of the proposed solution. The model preparation, including model pile configuration, model construction, sensor configuration, and frozen soil formation, were described in detail. The pile foundation lateral performance data, including failure mode observations, lateral load-displacement hysteresis relations, and moment distributions, were presented. The evolution of secant stiffness and energy dissipation of the pile-soil system with lateral displacement were analyzed and discussed. It was found that the peak lateral load of the model pile in 20 cm-thick seasonal frost is 53% larger than the unfrozen conditions. In contrast, the ultimate displacement in seasonally frozen conditions is 25% less than that in unfrozen conditions. And seasonal freezing can render a pile from ductile to brittle failure. More importantly, the results show that the local replacement with the proposed material can ensure similar lateral behavior for the soil-pile system under both unfrozen and frozen conditions. It is concluded that the proposed local replacement approach offers excellent potential for mitigating the adverse effects of seasonal freezing on the lateral performance of deep foundations in cold regions. In future studies, local replacement zone optimization and large-scale field tests are recommended to further confirm this method's effectiveness and provide design parameters for pilot testing.