Hysteresis Curve Morphological Characteristics of Polyurethane-Bonded Rubber Particle–Sand Mixture under Cyclic Loading at Freezing Temperatures

Polyurethane-bonded rubber particle–sand composite (PolyBRuS) is a promising material for replacing the soil surrounding pile foundations to mitigate the adverse effects of seasonally frozen ground on the seismic performance of bridge foundations in cold regions. This study describes the cyclic triaxial testing results of the PolyBRuS material subjected to various freeze–thaw cycles under different confining pressures and temperatures. The impact of temperature and confining pressure on the hysteretic behavior and the morphological characteristics are analyzed. The testing temperature, number of freeze–thaw cycles, and dynamic strain amplitude significantly impact the hysteretic behavior of the PolyBRuS material. However, the confining pressure ranging from 0 to 100 kPa has negligible influence. The dynamic stiffness of the material weakens with rising dynamic strain amplitude and freeze–thaw cycles but strengthens with increasing confining pressure and decreasing temperature. Meanwhile, the energy dissipation capacity of the material grows with decreasing temperature but remains insensitive to the confining pressure and freeze–thaw cycles. Compared with frozen clay, the dynamic stiffness of the PolyBRuS material is significantly lower, the energy dissipation capacity is substantially higher, and both are much less sensitive to temperature. This confirms the potential of the material in geotechnical isolation of seismic effects for deep foundations in cold regions. Empirical models are proposed to model the decay of dynamic stiffness and energy dissipation capacity with increasing loading cycles at various ambient conditions. These models can be used to simulate the hysteresis behavior of the PolyBRuS material.