Call number: LD2668 .T4 1936 B41

The hydraulic conductivity of sand-bentonite mixtures (SBMs) was measured to investigate the effects of mixing method, uniformity, and hydration of the mixtures. Triaxial tests were completed to determine the hydraulic conductivity of each specimen. Specimens using Ottawa sand and Wyoming bentonite, prepared with dry and suspension mixing conditions that altered the degree of hydration and swelling of bentonite, had varying bentonite content by percentage dry weight of sand. The conclusions of this experiment can be applied to the construction of cut off walls used in levees to mitigate groundwater seepage through underlying pervious layers. Eleven sand-bentonite specimens were tested in this study: nine were prepared using dry mixing and two were prepared using suspension mixing. The results do not show strong correlations between hydraulic conductivity and bentonite content, mixing method, clay void ratio, or time. Therefore, further investigation of the results was necessary. The bentonite void ratio (clay void ratio) assumes that bentonite is fully swelled for both blocked and partially blocked flow. Blocked flow occurs when the swelled bentonite blocks all the sand voids, forcing the water to flow within the bentonite voids. However, the results in this study shows that the concept of clay void ratio doesn’t capture the performance of SBMs when the bentonite is partially swelled; therefore, a new concept of effective clay void ratio was introduced to account for bentonite partial swelling. The effective clay void ratio determines the volume of swelled clay as a function of the volume of fully swelled bentonite. This is useful when comparing results with literature or predicting hydraulic conductivity in cases where only partial swelling of bentonite is expected. / text

Heavy mineral compositions of sands from Oregon beaches, rivers and sea cliffs have been determined in order to examine the causes of marked along-coast variations in the beach-sand mineralogy. The study area extends southward from the Columbia River to the Coquille River in southern Oregon. The heavy-mineral compositions were determined by standard microscopic identification with additional verification by X-ray diffraction analyses. Initially the beach-sand samples were collected as single grab samples from the mid-beachface, but significant selective sorting of the important heavy minerals prevented reasonable interpretations of the results. Factor analysis of multiple samples from the same beach yielded distinct factors which correspond with known mineral sorting patterns. The effects of local sorting were reduced by the subsequent use of large composite samples, permitting interpretations of along-coast variations in sand compositions. Four principal beach-sand sources are identified by factor analysis: the Columbia River on the north, a Coastal Range volcanic source, sands from the Umpqua River on the south-Oregon coast, and a metamorphic source from the Klamath Mountains of southern Oregon and northern California. The end members identified by factor analysis of the beach sands correspond closely to river-source compositions, the proportions in a specific beach-sand sample depending on its north to south location with respect to those sources. During lowered sea levels of the Late Pleistocene, the Columbia River supplied sand which was dispersed both to the north and south, its content decreasing southward as it mixed with sands from other sources. The distributions of minerals originating in the Klamath Mountains indicate that the net littoral drift was to the north during lowered sea levels. With a rise in sea level the longshore movement of sand was interrupted by headlands such that the Columbia River presently supplies beach sand southward only to the first headland, Tillamook Head. At that headland there is a marked change in mineralogy and in grain rounding with angular, recently-supplied sands to the north and rounded sands to the south. The results of this study indicate that the present-day central Oregon coast Consists of a series of beaches separated by headlands, the beach-sand compositions in part being relict, reflecting the along-coast mixing at lower sea levels and subsequent isolation by onshore migration of the beaches under the Holocene sea-level transgression. This pattern of relict compositions has been modified during the past several thousand years by some addition of sand to the beaches by sea-cliff erosion and contributions from the rivers draining the nearby Coastal Range. / Graduation date: 1987

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Recent studies have shown that the presence of sand ripples on the seabed improves sonar detection of buried mines at sub-critical angles. Sidescan sonar data of ripples off on the west Florida shelf were collected as part of ONR's Ripples Departmental Research Initiative (DRI) September 26-29th and November 7-9th, 2004. Hurricane Ivan, the strongest storm of the 2004 hurricane season, passed over the experiment site a week before the first data collection. This study focuses on the ripples created by Ivan. Average relict ripple wavelengths left after the storm were found to increase with water depth (50 cm, 62 cm, and 83 cm in 20, 30, and 50 meter water depths) despite the fact that orbital diameter decreases with water depth. Ripple prediction requires information about surface gravity waves and sediment grain size. The most reliable offshore wave field available was created with Wavewatch III by Naval Postgraduate School scientists. These waves were inputted into Delft3D WAVE, incorporating the nearshore wave model SWAN to predict waves at the locations where ripples were measured. Orbital motions at the seabed and grain size were inputted into a time-dependent ripple model with varying dissipation parameters to estimate sand ripples created by Hurricane Ivan. Ripple wavelength was found to be more strongly dependent on grain size than wave dissipation. / Contract number: N62271-97-G-0026. / US Navy (USN) author.

Sand casting is the most widely used casting process for both ferrous and non-ferrous alloys; however, the process is marred by large grain size structures and long solidification times. The coarser microstructure has a negative effect on the mechanical properties of the cast components and the long processing time affects the overall productivity of the process. The research reported herein addresses these problems for aluminum sand castings by enhancing the rate of heat extraction from the casting by replacing air, which is typically present in the pores of the sand mold and has a relatively low thermal conductivity by helium which has a thermal conductivity that is at least five times that of air in the temperature range of interest. The effect of (1) the flow rate of helium, (2) the way in which it is introduced into the mold, and (3) the mold design on (a) the average grain size, (b) the secondary dendrite arm spacing, and (c) the room temperature tensile properties of castings is investigated and compared to their counterparts produced in a typical sand casting process. In addition, a cost analysis of the helium-assisted sand casting process is performed and an optimum set of parameters are identified. It is found that when the helium-assisted sand casting process is performed with close to the optimum parameters it produces castings that exhibit a 22 percent increase in ultimate tensile strength and a 34 percent increase in yield strength with no significant loss of ductility, no degradation in the quality of the as-cast surfaces, and no significant increase in the overall cost.

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