Dynamic and post-dynamic shear strength of protecting expansive-clay liner on highways and environmental facilities

Compacted layers of natural expansive clay liners (ECLs) are commonly employed in geotechnical and geoenvironmental engineering as protective systems on highway slopes and shoulders, hydraulic barriers, and cover layers in waste containment facilities. During their service life, these liners are subjected to various dynamic loads arising from operational machinery and natural seismic activity. Ensuring their capacity to withstand such loads is critical for safe and effective design. In this study, compacted ECL specimens were subjected to up to 10,000 cycles of dynamic loading using a dynamic triaxial testing system. A range of cyclic stress ratios ( CSR = 0.25, 0.5, 1.0, 2.0, 2.5, 3.0, and 4.0) was applied to simulate the variability of dynamic and impact loads associated with heavy vehicular traffic and railways. The post-dynamic shear strength was measured and compared with the undisturbed shear strength before applying dynamic loads. Results indicated that the stress-strain response exhibited pronounced nonlinearity within the initial 100 loading cycles, as evidenced by the hysteresis loops. Based on the proposed failure criteria, a notable linear degradation in dynamic shear strength was observed for CSRs exceeding 1.0. A suitable model was developed to delineate the failure, critical, and stable response zones of the tested liners. Additionally, the post-dynamic shear strength increased by approximately 22% in specimens subjected to axial dynamic stresses greater than 100 kPa.