Cyclic Shear Behaviors of Geosynthetic-Soil Interface considering Chemical Effects

Abstract

Geosynthetics have been widely applied in waste landfill site for reinforcement, filtration, drainage, protection, and separation. Geosynthetics inevitably contact soil particle directly, composing 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 nonlinear responses. Recent studies have presented the behaviors of geosynthetic-soil systems are subjected to the interface shear strength degradation, which is affected by ambient factors such as the magnitude of normal stress, type of external loading and chemical conditions. In this study, particularly, the effects of chemical aggressors such as acidity and basicity from the leachate on the geosynthetic-soil interface were intensively investigated under cyclic shear loading to consider the dynamic condition, based on the experimental approach. The Multi-purpose Interface Apparatus (M-PIA) which is able to simulate the cyclic simple shear conditions of the interface was newly manufactured and modified for better performance. 72 sets of cyclic simple shear tests were conducted to inspect the effects of the pH values of leachate on the shear behavior of the geosynthetic-soil interface. Both geosynthetics and Jumunjin sand were submerged in acid, neutral, and basic solutions for 30 days and 850 days, representing relatively short-term and long-term behaviors of the interface, respectively. Test results displayed remarkable distinction in chemical degradation trends according to the pH values. The Disturbed State Concept (DSC) and disturbance function were introduced and employed to estimate shear stress degradation based on the experimental study, quantitatively. New disturbance functions and parameters that determine the characteristics of shear strength at the interface were mathematically evaluated. Furthermore, microscopic observation by Focused Ion Beam (FIB) was introduced and utilized to clarify the reason of the variation of interface damage subjected to the chemical conditions. As a result, the variation of the cyclic shear behavior at the geosynthetic-soil interface was due to the different damage patterns of the soil particle surface. Based on the experimental approach, the numerical back-prediction based on the DSC parametric study of the cyclic shear stress-strain behavior was performed to verify the accuracy and applicability of the DSC parameters. The back-prediction utilized the numerical interpolation from the test results and enabled to consider the shear stress degradation as load cycles, successfully. The shear strains were obtained from the average shear strain increment from the disturbance function curve and updated according to the load cycles. The comparison results between the experimental data and back-predicted results were found to be in good agreements. Consequently, a general methodology to estimate the cyclic shear stress degradation of geosynthetic-soil interface considering chemical effects has been established and verified.