JACK

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Stabilization and Imaging of Cohesionless Soil Specimens

abstract: This dissertation describes development of a procedure for obtaining high quality, optical grade sand coupons from frozen sand specimens of Ottawa 20/30 sand for image processing and analysis to quantify soil structure along with a methodology for quantifying the microstructure from the images. A technique for thawing and stabilizing frozen core samples was developed using optical grade Buehler® Epo-Tek® epoxy resin, a modified triaxial cell, a vacuum/reservoir chamber, a desiccator, and a moisture gauge. The uniform epoxy resin impregnation required proper drying of the soil specimen, application of appropriate confining pressure and vacuum levels, and epoxy mixing, de-airing and curing. The resulting stabilized sand specimen was sectioned into 10 mm thick coupons that were planed, ground, and polished with progressively finer diamond abrasive grit levels using the modified Allied HTP Inc. polishing method so that the soil structure could be accurately quantified using images obtained with the use of an optical microscopy technique. Illumination via Bright Field Microscopy was used to capture the images for subsequent image processing and sand microstructure analysis. The quality of resulting images and the validity of the subsequent image morphology analysis hinged largely on employment of a polishing and grinding technique that resulted in a flat, scratch free, reflective coupon surface characterized by minimal microstructure relief and good contrast between the sand particles and the surrounding epoxy resin. Subsequent image processing involved conversion of the color images first to gray scale images and then to binary images with the use of contrast and image adjustments, removal of noise and image artifacts, image filtering, and image segmentation. Mathematical morphology algorithms were used on the resulting binary images to further enhance image quality. The binary images were then used to calculate soil structure parameters that included particle roundness and sphericity, particle orientation variability represented by rose diagrams, statistics on the local void ratio variability as a function of the sample size, and the local void ratio distribution histograms using Oda's method and Voronoi tessellation method, including the skewness, kurtosis, and entropy of a gamma cumulative probability distribution fit to the local void ratio distribution.Dissertation/ThesisM.S. Civil Engineering 201

The influence of magnetic cohesion on the stability of granular slopes

This thesis presents an investigation into the influence of magnetic cohesion on the stability of granular slopes. We consider magnetic cohesion that results from the interaction between dipole moments induced in grains by a uniform magnetic field. The repose angle of spheres is known to increase much more slowly with magnetic cohesion than in experiments with liquid-bridge cohesion. To our knowledge, nowhere in the literature has anyone offered a satisfactory explanation of this discrepancy. Our two-dimensional molecular dynamics simulations of granular piles show that shear occurs deep in the pile. The addition of a magnetic field causes the motion to shift farther down into the pile, preventing the angle from increasing substantially. We investigate different models of wall friction, and discover that wall interactions have a significant influence on the rate of increase of the slope angle with magnetic cohesion. In three-dimensional simulations we observe an initial decrease in the repose angle as the cohesion is increased, contrary to expectations. We explain this effect by considering how the transverse magnetic force influences the particle distribution of the pile. In contrast, draining-crater experiments reveal that the angle of repose of diamagnetic bismuth grains increases dramatically with cohesion in a vertical field. We argue that this difference is due to the non-spherical shape of the grains, and investigate further the influence of grain shape by using non-magnetic `voids' of different shapes in a paramagnetic solution. We discover a strong positive correlation between the grain aspect ratio and the size of the effect of magnetic cohesion on the slope angle. This is because a non-spherical grain accumulates magnetic charge on sharp edges and corners, increasing the magnetic field in its immediate vicinity and leading to stronger interactions with neighbouring grains. Also, in piles of grains with larger aspect ratios, avalanches occur closer to the surface, thus increasing the stability of the pile

The behaviour and habitat use of red deer (Cervus elaphus) in the flow country of Sutherland

Not availabl