A Conceptual Geogrid–Soil Interaction Framework for GRS Integral Abutments under Cyclic Deck Movements

Geosynthetic reinforced soil (GRS) integral bridge abutments are subjected to cyclic horizontal displacements induced by seasonal thermal expansion/contraction of bridge decks, resulting in progressive settlement and lateral earth pressure development. While previous studies have primarily focused on deformation performance, the evolution of soil-reinforcement interaction mechanisms governing cyclic response remains insufficiently understood. This study investigates the cyclic behavior of four scaled physical models of GRS integral abutment with varying facing and reinforcement arrangements subjected to active (CA), passive (CP) and combined (CAP) loading over 100 cycles at different displacement amplitudes and loading rates. A rate-normalization framework was developed by combining experimental observations with validated numerical simulations and was independently verified using published datasets. Sensitivity analysis indicates that displacement amplitude is the primary factor controlling settlement accumulation and lateral pressure mobilization, whereas loading rate and number of cycles govern the rate of response evolution. Settlement under CA loading exhibited the greatest sensitivity to loading rate, while CP produced the strongest rate dependency in lateral earth pressure. Strain distributions and transition plots revealed progressive changes in reinforcement distress, supporting the proposed mechanistic framework comprising Facing Interaction (FI), Tension Anchorage (TA) and Composite Stabilization (CS) providing basis for interpreting long-term cyclic response.