Multi-scale assessment of geotextile-geomembrane interaction

The interface strength between geotextiles and geomembranes is typically a critical factor governing the stability of slopes that incorporate geosynthetics since the double layer lining system was legislated as the national specification for landfills in the United States in the mid 1980s. Previous researchers have focused on the large-scale interaction of fiber-texture interfaces while the micromechanical behavior of the internal geotextile structure has received limited attention. Characterizing the variation in the arrangement and distribution of filaments and/or voids is essential to understanding the micro-scale mechanisms of nonwoven fabrics interacting with textured counterface materials. This thesis presents the results from a study that examined the micromechanical mechanisms involved at needle-punched nonwoven geotextile-textured HDPE geomembrane interfaces and relates the results to the observed macro-scale response.; A large displacement direct interface shear device was developed and used in this study to reduce the system errors that often occur with conventional shear devices and to allow internal geotextile strains to occur during shear. Complimentary numerical modeling was undertaken to study the interface response. The effects of boundary conditions and materials properties on the interface response were quantified. An advanced image analysis technique was used to allow the evolution of the filament microstructure under various boundary and load conditions to be quantified. The different phases within the geosynthetic interface zone were detected from images captured using high-resolution optical microscopy. The changes of geotextile internal structure were statistically quantified in terms of inter-filament distances as well as the local void ratio and inscribing void size distributions. The tensile response of single filaments was measured using a helium neon deflectometer and these measurements were used to evaluate the shear induced filament strain.; It was found that the geotextile strain critically affected the geotextile-geomembrane interface shear response as well as the variation in the internal filament structure. The three orthogonal viewing planes and the serially sectioned surface images in the vertical direction revealed localized filament concentrations around texture elements. The locations of concentrations were consistent with the shear direction and texture geometry. Shearing resulted in significant variation of the geotextile filament structure due to localized stretching of filaments and surface degradation of geotextile near the interface. The inter-filament distance changes as well as the local void ratio distribution reflected the significant response of the geotextile to the normal and shear stress states. The sizes of voids enclosed by adjacent filaments were measured using optical image analysis and expressed in terms of the largest inscribing opening size (LIOS). LIOS was particularly useful for quantifying the structure of horizontal surfaces at different depths with the geotextile specimen, where the filament network consisted of long curved features. The interface shearing of a geotextile against a textured geomembrane resulted in a distinct reduction of the filament diameter distribution reflecting the tensile force effects on the individual filaments. The minimum filament diameter was observed at peak shear. The test results showed the impact of the concentrated normal stress and micromechanical interlocking between the geomembrane textures and geotextile filaments during interface shearing. This study provides micromechanical insight into the combined role of geomembrane surface topography and geotextile filament structure on macro-scale geosynthetic interface response.