Graduation date: 1999

A parametric analysis of typical base isolated bridges was conducted. The bridges were located in different soil types and were subjected to three different earthquakes (recorded on soft and medium soils). The work had two main objectives: to asses the effects of the nonlinear behavior of the isolation pads of the bridges on the seismic responses (accelerations, displacements, and pier seismic forces), and to study combined effects of base isolation and inertial interaction due to the presence of flexible foundations. The analytical models used for the study were selected on the basis of initial evaluation of different models proposed in the literature to represent a bridge structure and to evaluate the isolation pads’ nonlinear behavior. The bridges studied were developed with a three-dimensional model. After completing the studies, 2 degree of freedom models were used to investigate more general trends of the inertial SSI effects for the base isolated bridges. The results of the work show the efficiency of base isolation pads in improving the seismic performance of bridges in most cases. They suggest that the inertial SSI effects will not be generally important for bridge foundations designed with a factor of safety of 3, with more than one line of piles in either direction since they will be very stiff foundations. But they also showed that for slender piers it is important to carefully evaluate the translations on top of the piers due to the rocking effects of the foundation.

A continuous formulation to calculate the dynamic stiffness matrix of structural members with distributed masses is presented in detail and verified with some simple examples. The dynamic model of a specific bridge (the Marga-Marga bridge in Chile) was developed using this formulation, and the model was then used to obtain the transfer functions of the motions at different points of the bridge due to seismic excitation. The model included rubber pads, used for base isolation, as additional members. The transfer functions were obtained with and without rubber pads to investigate their effect. The dynamic stiffness of complete pile foundations was calculated by a semi-analytical solution with Poulos?? assumption. General observations on group effects under various conditions were obtained from the result of these studies. The dynamic stiffness of the pile foundations for the Marga-Marga bridge was then obtained and used to study the soil structure interaction effects on the seismic response of the bridge. Records obtained during a real earthquake were examined and interpreted in light of the results from all these analyses. Finally, conclusions and recommendations on future studies are presented.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 218-220). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Phil.)--University of Hong Kong, 1984.

No description available.

Earthworms are well known for their casting and burrowing activities which improve soil structure and soil fertility. However, earthworm populations in temperate regions exhibit patchy distribution in space and time. This makes it difficult to predict how earthworm activities may influence paedogenesis and nutrient cycling processes at the ecosystem level. The main objective of this study was to determine the spatiotemporal dynamic of surface cast production of two earthworm species, Aporrectodea turgida and Lumbricus terrestris, on the row-interrow scale in a temperate soybean agroecosystem. Our observations demonstrated that casting activity was synchronous with plant growth. More casts were also found in the row intercepts compared to the interrow ones. Both the spatial and temporal variations are thought to be caused by the microclimate found under the plant canopy, verifying results from controlled laboratory studies that show casting activity to be controlled by soil temperature and moisture. These results suggest a possible mutualism between earthworm and plants in cultivated temperate soybean agroecosystems, but this remained to be confirmed.

Under intensive farming, soil structure degradation and soil erosion are primarily associated with losses of organic matter. Restoration of soil structure may depend on the amount and nature of the organic amendment added. The effect of the addition of humic and fibric materials, and beeswax, a naturally occurring source of long-chain aliphatics comparable to those present in humic materials, on microbial activity and the structural properties of a waterlogged silty clay low in organic carbon was investigated. The incorporation of the fibric material increased the microbial activity in proportion to the amount of material added, whereas the humic and beeswax materials had the opposite effect. All organic materials added increased the cohesion of aggregates due to non water-dispersible cements. The fibric material was predominantly composed of polysaccharides and large quantities were required to produce a positive effect. The humic material was mainly lipids and the effect was associated with the time of incubation rather than the amount of material added. Principal-component analysis showed that the humic material was more effective at stabilizing soil aggregates than the fibric material, although the fibric material had a greater effect on the resistance of aggregates to slaking forces. Further testing with beeswax showed that the clay-associated lipids increased by 3.5-4.0 times the resistance of soil aggregates to the slaking forces, whereas the effect of hydrophobic "free" lipids was transient and accessory by coating and embedding soil aggregates.

No description available.

The objective of this study was to determine the correlation between potentiometric surface and the depth to selected soil morphological indicators of wetness for the Glynwood (Aquic Hapludalf), Blount (Aeric Epiaqulaf), and Pewamo (Typic Argiaguoll) soils in Delaware County, Indiana. Four years of potentiometric surface measurements were averaged and compared to detailed soil descriptions performed by the Natural Resources Conservation Service. Significant correlations exist between the morphological indicators and the potentiometric surface for the Glynwood (moderately well drained) 2-m depth piezometers and 2-m depth slotted pipes, the Blount (somewhat poorly drained) top of the C horizon and 2-m depth piezometers, and the Pewamo (poorly drained) top of the B horizon piezometers. The relationships among the horizons in which potentiometric surface correlated to indicator depth may be a function of the increased persistence and shallowness of the potentiometric surface in mid-April. / Department of Natural Resources and Environmental Management