Environmental conditions such as temperature inevitably impact the long term performance, strength and deformation characteristics of most materials in infrastructure applications. The mechanical and durability properties of geosynthetic materials are strongly temperature dependent. The interfaces between geotextiles and geomembranes as well as between granular materials such as sands and geomembranes in landfill applications are subject to temperature changes due to seasonal temperature variations as well as exothermic reactions occurring in the waste body. This can be a critical factor governing the stability of modern waste containment lining systems. Historically, most laboratory geosynthetic interface testing has been performed at room temperature. Information today is emerging that shows how temperatures in the liner systems of landfills can be much higher. An extensive research study was undertaken in an effort to investigate temperature effects on interface shear behavior between (a) NPNW polypropylene geotextiles and both smooth PVC as well as smooth and textured HDPE geomembranes and (b) sands of different angularity and smooth PVC and HDPE geomembranes. A temperature controlled chamber was designed and developed to simulate elevated temperature field conditions and shear displacement-failure mechanisms at these higher temperatures. The physical laboratory testing program consisted of multiple series of interface shear tests between material combinations found in landfill applications under a range of normal stress levels from 10 to 400 kPa and at a range of test temperatures from 20 to 50 °C. Complementary geotextile single filament tensile tests were performed at different temperatures using a dynamic thermo-mechanical analyzer (DMA) to evaluate tensile strength properties of geotextile single filaments at elevated temperatures. The single filament studies are important since the interface strength between geotextiles and geomembranes is controlled by the fabric global matrix properties as well as the micro-scale characteristics of the geotextile and how it interacts with the geomembrane macro-topography. The peak interface strength for sand-geomembrane as well as geotextile-geomembrane interfaces depends on the geomembrane properties such as hardness and micro texture. To this end, the surface hardness of smooth HDPE and PVC geomembrane samples was measured at different temperatures in the temperature controlled chamber to evaluate how temperature changes affect the interface shear behavior and strength of geomembranes in combination with granular materials and/or geotextiles. The focus of this portion of the experimental work was to examine: i) the change in geomembrane hardness with temperature; ii) develop empirical relationships to predict shear strength properties of sand - geomembrane interfaces as a function of temperature; and iii) compare the results of empirically predicted frictional shear strength properties with the results of direct measurements from the interface shear tests performed at different elevated temperatures.

Vortex breakdown is an important phenomenon observed in swirling flows involving the development of a stagnation point on the axis of the vortex followed by a region of recirculation when the swirl increases beyond a particular level. It has been studied extensively over past 50 years and various theories have been proposed to explain its various aspects. However, a single model explaining all the aspects together is yet to emerge. Numerical simulations of breakdown have been performed using a variety of grid-based as well as vortex methods. Vortex methods are a Lagrangian alternative to grid-based methods wherein the motion of the vorticity is determined by the local fluid velocity convection, with models for viscous effects when considered. The fluid velocity is obtained from the vorticity field. Only the rotational regions of the flow need to be considered leading to significant economy of computational effort for simulations of vorticity dominated flows, such as vortex breakdown. The inviscid vortex filament method has been used to simulate several aspects of the vortex breakdown phenomenon. The vortex filament method however, cannot easily simulate viscous effects. To simulate the viscous effects the viscous vortex particle method needs to be used. This work was intended to be a first step towards this end by initially evaluating the effectiveness of the inviscid version of the vortex particle method in simulating the breakdown phenomenon. The inviscid vortex particle method was found to satisfactorily simulate most qualitative aspects involved in the formation of vortex breakdown such as the retardation of axial velocity along centerline, radial swelling of the vortex core, formation of stagnation points, creation of azimuthal vorticity gradient from axial vorticity gradient and the turning of vortex lines along with the formation of a bubble-like structure with recirculating flow within. The effect of a wall placed adjacent to the vortex core was simulated by using image vortices. The wall was not found to influence the location of breakdown. However, the initiation of the spiral mode was found to occur earlier when a wall was present. For a quantitative assessment, a simulation of the experimental results of Faler and Leibovich (1978) was attempted. The simulation managed to predict the location of the breakdown and the extent of the bubble. The shape and height of the bubble obtained however were not in accord with the experimental observations. A single vortical cell was obtained in the interior of the bubble.