Behavior of Fine-Grained Residual Soil under Cyclic Loading

This study investigated the dynamic behavior of fine-grained lateritic soils under one-way, stress-controlled cyclic triaxial testing in undrained conditions, focusing on deformation patterns, resilient modulus, strain-dependent shear modulus, and damping properties. The results showed that, similarly to other geomaterials, lateritic soils under cyclic loading undergo three distinct deformation phases: plastic shakedown, plastic creep, and incremental collapse. Key factors impacting these behaviors include the cyclic stress ratio (CSR), number of loading cycles, pore-water pressure, and loading frequency. The findings show that permanent deformation increases with increased CSR and loading cycles, but decreases with higher frequency, though frequency effects are less significant at lower CSR levels. The accumulation of pore-water pressure contributes significantly to deformation, with effective stress paths moving closer to the failure envelope, suggesting that pore-water pressure ratios are valuable for assessing soil stability. A critical CSR threshold (CSRcr) of 0.44 was identified via shakedown theory. Although CSR values below 0.44 seem to be safer, degradation indices indicate potential serviceability risks even within this range, prompting a need for a multifactorial approach to CSR assessment. In this context, combining the degradation index, pore-water pressure ratio, and effective stress path analysis indicates that a more accurate CSRcr is 0.37. Additionally, findings indicate that increased CSR leads to an increase of damping ratio and a reduction of resilient modulus, which is attributed to the degradation of interparticle bonding from elevated pore-water pressures. A relationship between resilient modulus and damping ratio is introduced, reflecting the soil’s dynamic response under cyclic conditions. Strain-dependent shear modulus and damping curves, which are essential for geotechnical modeling, were established, along with a new correlation between damping and normalized shear modulus reduction, enhancing the modeling accuracy for lateritic soils.