Influence of surface topography on interface strength and counterface soil structure

Numerous man-made construction materials such as geomembranes, geotextiles, and geogrids, are being routinely used in conjunction with soils and rocks in geotechnical engineering applications. For economic and technical reasons, the demand for these composite soil-synthetic material systems is continuously increasing. The placement of these materials adjacent to one another creates interfaces which can have relatively weak shear strengths compared to the shear strength of the soil mass itself and thus slippage or relative movement may occur. Accordingly, design involving such materials is often controlled by the shear strength of the interface.; This thesis presents the results of investigations into the behavior of geomembranes in contact with geotextiles as well as granular soils to study the shear mechanisms as a function of geomembrane surface roughness. Accordingly, the goals of this research were to: (1) enhance an existing method to characterize the topography of geomaterial interfaces; (2) study the interface shear behavior between geomembranes and geotextiles; (3) study the interface shear mechanisms between granular materials and geomembranes; and (4) provide recommendations for design in the context of the materials used in this study. This study involved characterizing the surface roughness of geomembranes using the Optical Profile Microscopy (OPM) method. The shear behaviors between both granular soils and geomembranes as well as geotextiles and geomembranes were examined by conducting tests with geomembranes of varying roughness in a large displacement interface shear device.; It was found that surface roughness has a first-order effect on the shear behavior of geomembrane/geotextile interfaces. It is considered that the sliding of the geotextiles, is the main mechanism for the smooth geomembrane surfaces, however pulling out and tearing of the filaments from the geotextiles, and the removal of texture at asperities from the geomembranes are key failure mechanisms for textured geomembrane surfaces.; It was also found that the shear mechanism for granular soil/geomembrane interfaces is dramatically changed by the geomembrane surface roughness. Quantitative analysis of the evolution of the sand structure was performed using image analysis. For the smooth geomembranes, the shear strength is developed by sliding and plowing of sand particles, while for the textured geomembranes, the strength results from the interlocking and dilation of sand particles. The angularity of sand particles induces higher plowing effects on the smooth geomembrane resulting in higher residual friction angles than rounded to subrounded sand.