Behavior of unsaturated sandy loess under high-frequency unilateral cyclic loading.

Sandy loess, which is distinguished by its granular composition dominated by sand particles and minimal clay, is vulnerable to structural destabilization under cyclic loading. This report focuses on recurrent geotechnical failures in the hydrocarbon extraction zones of China's Loess Plateau. The investigation employs cyclic triaxial testing to evaluate the moisture-dependent and frequency-governed mechanical behaviors of unsaturated sandy loess, particularly in the context of the Maliancheng Village landslide event. Beyond the plastic limit threshold, the moisture content has negligible effects on the stress-strain hysteresis, shear rigidity, and energy dissipation of the system. However, sub-plastic-limit conditions induce strain amplification by increasing damping ratios and decreasing shear resistance. Meanwhile, the strain magnitude and shear stiffness increase proportionally with loading frequency, whereas damping responses have an inverse frequency relationship. Notably, high-rate cyclic loads have less of an influence on early-phase mechanical signatures. Progressive strain accumulation under sustained high-frequency loading follows triphasic evolution, i.e., exponential escalation, transitional refinement, and metastable equilibrium, while stabilization cycles escalate nonlinearly as a function of the applied stress.