Development of modified interface apparatus and prototype cyclic simple shear test considering chemical and thermal effects

Abstract

Geosynthetics are widely used at waste landfill sites due to their mechanical and physical advantages. Geosynthetics inevitably involve interface problems corresponding to the parametric conditions, which affect the shear behavior of the geosynthetic-soil interface. In this research, chemical and thermal effects were considered in an investigation of the cyclic shear behavior of the geosynthetic-soil interface. The modified multipurpose interface apparatus (M-PIA), which was able to consider thermal condition, was introduced, and major modifications and improvements of the structure and units were described. Displacement capacity to reach peak strength subjected to the specimen size was verified by the static tests. Prototype cyclic simple shear tests were performed, and the disturbed state concept (DSC) was utilized to estimate quantitatively the cyclic shear stress degradation of the interface. The pH values of the solutions represented the chemical condition of the leachate because the pH value changed dramatically due to complicated biochemical reactions in the leachate (Bilgili et al. 2007, "Metal Concentrations of Simulated Aerobic and Anaerobic Pilot Scale Landfill Reactors," J. Hazard. Mater., Vol. 145, Nos. 1-2, pp. 186-194), and pH was considered to be the most significant parameter affecting leachate concentration (Rafizul and Alamgir 2012, "Characterization and Tropical Seasonal Variation of Leachate: Results From Landfill Lysimeter Studied," Waste Manage., Vol. 32, No. 11, pp. 2080-2095). Specimen temperatures of 20 and 60 degrees C were applied and maintained during the tests to approximate the thermal conditions inside of the waste landfill. As a result, shear stress degradation with an increasing number of cycles was observed, and the greatest interface disturbance appeared under the acidic condition. The rapid increase in the disturbance was observed at a high temperature in acid and basic conditions; however, the disturbance function curves under the neutral condition were nearly identical despite the different temperatures. Therefore, it was deduced that an elevated temperature can degrade the shear resistance of the geosynthetic-soil interface under severe acid and basic conditions. An elevated temperature under a neutral condition did not affect the shape of the disturbance function curves.