A geomembrane, or GMB, is a flexible synthetic liner used to control fluid migration in manmade projects. These thin polymeric sheets are ideal for geotechnical engineering projects to prevent soil and groundwater contamination. Its impermeability makes it ideal in landfills, but its shear strength is relatively low, so when combined with compacted clay liners (known as CCL), there are cases of sliding instability and failure. While there has been a range of studies on shear behavior, there has been limited research specific to the dynamic shear characteristics of GMB/CCL composite liner interfaces. The authors of a recent paper in the Journal of Geotechnical and Geoenvironmental Engineering took into consideration the number of older landfills in the world and focused their research on aging GMB/CCL interfaces.
Researchers Dian Chen, Yong-Gui Chen, Yong-Feng Deng, Wei-Min Ye, Dai-Cheng Ye, and Juan Hou investigated the impact of aging on the vertical displacement, stress–displacement relationship, dynamic shear strength, dynamic shear stiffness, and damping ratio of the GMB/CCL interface. Using 18-year-old samples obtained from a landfill in Xiamen City, the authors performed a total of 27 displacement-controlled cyclic direct shear tests on three types of GMB/CCL interfaces, presented in “Interface Dynamic Shear Characteristics of Aging GMB/CCL Composite Liner.” Learn more about how this study can serve as a reference when analyzing the dynamic stability of landfills during long-term use. Get the full results at https://doi.org/10.1061/JGGEFK.GTENG-12563. The abstract is below.
Abstract
Aging degradation of the geomembrane (GMB) significantly influences the dynamic shear characteristics of the composite liner interface, which comprises the GMB and the compacted clay liner (CCL), potentially jeopardizing the dynamic stability of landfills. In this study, cyclic shear tests were performed on two types of aging GMB/CCL interfaces, concurrently with shear tests on the nonaging GMB/CCL interface for comparison. The results suggest that the impact of aging on the dynamic shear characteristics of the GMB/CCL interface is essentially governed by the surface roughness and brittleness of the GMB, with the effect degree of brittleness influenced by the normal stress. Under low normal stress, aging increased the vertical displacement, dynamic shear strength, and shear stiffness of the GMB/CCL interface. However, under high normal stress, the dynamic shear strength and shear stiffness of the aging GMB/CCL interface were more likely to be lower than those of the nonaging interface. As the displacement amplitude increased, the influence of aging on the shear stiffness of the GMB/CCL interface gradually diminished. Aging also reduced the damping ratio of the GMB/CCL interface. The difference in vertical displacement between the exposed GMB/CCL interface and the in soil GMB/CCL interface caused by brittleness was not significant. In practical engineering, when the overlying load on the GMB/CCL composite liner is relatively small, aging makes the GMB more susceptible to tearing under seismic loads, whereas with larger overlying loads, aging is more likely to increase the shear displacement, thereby increasing the likelihood of instability in landfill. Finally, based on classic models of soil, fitting models for the normalized shear stiffness and damping ratio of the GMB/CCL interface were established and validated. This study can provide reference for analyzing the dynamic stability of landfills during long-term use.
Learn how you can apply this to your landfill maintenance in the ASCE Library: https://doi.org/10.1061/JGGEFK.GTENG-12563.
