Scholarship & Research
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Item A continuum mixture theory applied to stress waves in snow(Montana State University - Bozeman, College of Engineering, 1991) Austiguy, George EdwardIn avalanche control work the types of explosives and delivery methods used are primarily determined by trial and error. Understanding the propagation of stress waves in snow is a step towards eliminating some of this guesswork. A continuum theory of mixtures is applied to model snow as a mixture of an elastic solid and an elastic fluid. Three wave types, two dilational and one rotational wave are shown to exist. Theoretical expressions are developed for the wave attenuation and propagation velocity of each of the wave types. Numerical evaluation shows velocity and attenuation increasing with frequency for all three waves. Wave velocity increases with increasing density while attenuation decreases with increasing density for all three waves. The first dilational wave has a slow wave speed and is highly attenuated. This wave exhibits diffusive behavior at low frequencies and nondispersive behavior at high frequencies. The second dilation wave is the fastest of the three wave types and does not appreciably attenuate. Nondispersive wave behavior characterizes this wave at low and high frequencies. The rotational wave is the least attenuated of all three waves and propagates at velocities greater than that of the first dilational . wave but less than that of the second dilational wave. The rotational wave exhibits nondispersive behavior at low and high frequencies. Wave velocities and attenuation show behavior that is in agreement with existing experimental data.Item Axial capacity of piles supported on intermediate geomaterials(Montana State University - Bozeman, College of Engineering, 2008) Brooks, Heather Margaret; Chairperson, Graduate Committee: Robert L. MokwaPile foundations used to support bridges and other structures are designed and installed to sustain axial and lateral loads without failing in bearing capacity and without undergoing excessive movements. The axial load-carrying capacity of a driven pile is derived from friction or adhesion along the pile shaft and by compressive resistance at the pile tip. There are well established analytical methods for evaluating pile capacity and for predicting pile driving characteristics for cohesive soil, cohesionless soil, and rock. However, past experience indicates these methods may not be reliable for piles driven into intermediate geomaterials (IGMs), which often exhibit a wide array of properties with characteristics ranging from stiff or hard soil to soft weathered rock. Methods to determine the axial capacity, driving resistance, and long-term resistance of piles driven into intermediate geomaterials are not well established. Nine projects, in which piles were driven into IGMs, from the Montana Department of Transportation were analyzed. Each project contained information from CAPWAP dynamic analyses, construction records, and design reports. The purpose of any analyses, of the nine projects, was to better predict the behavior of piles in IGMs. IGMs were divided into two broad types, cohesive and cohesionless. The computer program DRIVEN is often used to predict the axial capacities of piles; however, in IGMs the design method is unreliable. Attempts were made to determine trends within the available data. Normalized resistances for shaft and toe capacities did yield slight correlations of shaft resistance to pile length in IGMs. Iterative solutions using DRIVEN to match the CAPWAP ultimate capacity did not provide meaningful trends or correlations. Slight modification of MDT's original DRIVEN inputs was required in most cases to match the CAPWAP ultimate capacity. Because no meaningful trends were found from analysis, other capacity calculation methods were used to determine other methods that accurately predict pile capacity within IGMs. The Washington Department of Transportation Gates formula is the most accurate method of those attempted. More research is required for further analysis of piles in IGMs.