Modified Cyclic Shear Test for Evaluating Disturbance Function and Numerical Formulation of Geosynthetic-Soil Interface Considering Chemical Effect

Geosynthetics have been broadly used in waste landfill sites for filtration, drainage, and separation. Geosynthetics contact soil directly, creating a geosynthetic-soil interface corresponding to the external forces and conditions. The differences in the intrinsic material characteristics at the interface induce complicated stress strain behaviors and strain-softening processes. Recent studies have presented the behaviors of geosynthetic-soil systems as depending on the interface shear strength degradation, which is affected by ambient factors such as the water content, chemical condition, etc. In this study, the disturbed state concept (DSC) and a disturbance function are introduced to explain the cyclic shear stress behavior of the interface. The degree of interface damage can be expressed by the disturbance function, and the shape of the disturbance function curve represents the intrinsic characteristics of the material. Massive sets of cyclic shear tests have been performed to investigate the effects of the pH values of leachates on the shear behavior of the geosynthetic-soil interface. Both geosynthetics and Jumunjin sand have been submerged in acid, neutral, and basic solutions for 200 days. A multi-purpose interface apparatus that can simulate the cyclic shear conditions of a geosynthetic-soil interface has been newly manufactured and modified for better performance. Test results display remarkable distinction in chemical degradation trends according to the pH values. New disturbance function parameters that determine the characteristics of the shear strength of the interface were estimated according to the chemical conditions as well. Furthermore, it was discovered via focused ion beam electronic microscopy that the different patterns of damage on the surface of soil particles with different pH values induce variation in the disturbance phase at the geosynthetic-soil interface. For the numerical formulation of the disturbance function, the constitutive equations of the DSC were modified using the Mohr Coulomb model. Based on the modified DSC equations, verification and numerical implementation shall be performed for further study.