Effect of Non-Plastic Fines and Cyclic Stress Ratio on Post-Cyclic Resistance of Bushehr Calcareous Sand

Estimating the post-cyclic resistance of soils in practical geotechnical projects is essential for predicting settlements and bearing capacity, particularly in regions susceptible to earthquake loading. Understanding the effects of fines content on post-cyclic monotonic resistance contributes to safer geotechnical design and mitigates the risk of foundation failure due to strength loss after seismic events. While the post-cyclic behavior of siliceous sands has been widely studied, limited research exists on calcareous mixed soils, whichhave different physical and mechanical properties comparedto siliceous sands. This study investigates the role of non-plastic fine content and cyclic stress ratio (CSR) on the post-cyclic resistance of Bushehr calcareous sand, which is extracted from a coastal region with high-seismicity risk. Undrained monotonic triaxial tests were performed after termination of cyclic tests on calcareous sands combined with various silt contents (0%, 10%, 20%, 30%, and 40%) and subjected to different CSRs to induce liquefaction. Post-cyclic resistance of samples was compared with shear resistance in monotonic tests. The results indicate that CSR influences post-cyclic resistance in two different ways depending on silt content: at lower fines content (0–10%), CSR improves post-cyclic resistance, whereas at higher fines content (20–40%), it leads to a reduction in strength. These findings provide crucial insightsinto offshore geotechnical safety and risk management by highlighting the post-cyclic behavior of calcareous soils, which is essential for geotechnical design in regions susceptible to seismic events.

Keywords: Post-cyclic resistance, Calcareous silty sand, Effect of fine content, Cyclic stress ratio,Cyclic triaxial tests, Liquefaction, Offshore geotechnical safety.