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published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Selected components of the water and energy balances at the surface of a bare clay loam were measured at 57 locations in a 1 ha field. Spatial and temporal variability of these components were also studied. Components included evaporation, irrigation, moisture storage, sensible heat flux and long wave radiation. Sub-studies were conducted on irrigation uniformity under low pressure sprinklers; and, on steel versus plastic microlysimeters (ML) of various lengths. An energy balance model of evaporation, requiring minimal inputs, was developed and validated giving an r$\sp2$ value of 0.78. Model improvements included an easy method of accurately estimating soil surface temperature at many points in a field, and an empirically fitted transfer coefficient function for the sensible heat flux from the reference dry soil. The omission of soil heat flux and reflected shortwave radiation terms was shown to reduce model accuracy. Steel ML underestimated cumulative evaporation compared to plastic ML at 20 and 30 cm lengths. Cumulative evaporation increased with ML length. The 10 and 20 cm ML were too short for use over multiple days but 30 cm ML may not be long enough for extended periods. Daily net soil heat flux for steel ML averaged 44% higher than that for both plastic ML and undisturbed field soil. Christiansen's uniformity coefficient (UCC) was close to 0.83 for each of 3 irrigations when measured by both catch cans and by profile water contents. But UCC for the change in storage due to irrigation averaged only 0.43 indicating than the high uniformity of profile water contents was more due to surface and subsurface redistribution than to the uniformity of application. Profile water contents and catch can depths were time invariant across at least 3 irrigations. Midday soil surface temperatures and daily evaporation were somewhat less time invariant. Variogram plots for evaporation and surface temperature showed mostly random behavior. Relative variograms represented well the spatial variability of both catch can depths and profile water contents. A strong link was demonstrated between the time invariance of a variable and the usefulness of kriging on that variable.

A linear distribution isotherm described the sorption/desorption of four phenols on the Pima clay loam soil. The linear distribution coefficients for 2,4-dichlorophenol, 2-chlorophenol, phenol and 2,4,6-trichlorophenol were 3.61, 2.93, 0.87, and 0.79. Ionization of the phenols affected their relative distribution order. Hydrogen bonding of phenols to exposed mineral sites accounted for the greater measured sorption than was predicted. The effect of solid concentration on the distribution of phenols was tested over a 10-fold soil/solution range. When a log transformation was performed on the data, a highly significant inverse relationship existed between the distribution of phenols and the soil/solution ratio. A 3-fold increase in the dissolved organic carbon in solution was associated with the decrease in the distribution coefficient. A 3-fold increase in the fraction organic carbon in the soil occurred when dry sludge solids were added to the Pima soil. A substantial increase in the dissolved organic carbon in solution was associated with the addition of sludge solids to the soil. (Abstract shortened with permission of author.)

In the true triaxial test procedure used for testing laboratory-prepared kaolinite clay samples, undrained (with constant mean stress) strength tests were conducted to study the yield and failure of the clays. The principle concern focussed around the influence of orientation of particle bedding plane on the development of yield and failure characteristics of the clay. As the true triaxial cell permits variations of the three principal stresses, it was possible to study the soil response in any chosen quadrant of the principal space. / As a consequence to what is mentioned above, two types of consolidated undrained true triaxial tests were conducted in this study. In the first type, specimens were trimmed from the block sample with 90, 60, 30 and 0 degree orientation angles of particle's bedding planes; these angles were measured with respect to the direction of the major principal stress axis. For each degree of inclination, specimens were tested with three confining pressures 207, 276 and 345 kPa, and for each value of confining pressure, the loading path was varied from compression to tension. / The degree of dissociation between the stress and strain increment vectors was seen to depend on both initial and stress induced anisotropy. / Most important of all, a constitutive relationship for anisotropic kaolinite clay was derived on the basis of the observed experimental behaviour of soil samples under loading. / Additionally, anisotropy is characterized by a double transformation technique. The first transformation accounts for the directional dependency whilst the second transformation concerns itself with anisotropy of the base vectors. The relative joint invariant principle is used to calculate the degree of dissociation during the loading process. The variation of the dissociation angle during the loading process can be considered as a measure of the evolution of the resultant anisotropy. The model has shown to provide viable predictions of the stress-strain relationships obtained from true triaxial tests on an anisotropic kaolinite clay for: (a) different inclinations of particle's bedding planes, (b) different stress paths in one sector, (c) different stress paths in other sectors, and (d) the failure surfaces for different inclinations of particle's bedding planes in the octahedral plane. (Abstract shortened with permission of author.)

The performance of a subsurface irrigation system in a clay soil was investigated under field conditions from 1989 to 1991. It was found that subsurface irrigation could be practised successfully in some clay soils of Quebec. The 10 m drain spacing was found to be better than the 20 m drain spacing in terms of keeping a uniform water table between the drains. The water table distribution between the drains was found to be a factor of the applied hydraulic head. The relationship between the applied hydraulic head and the midspan water table elevation could not be determined due to unfavourable weather conditions during the study period. The soil moisture content was found to follow the same behavior as the water table elevation, however, the relationship between these two parameters could not be properly established. It was also found that under the same applied hydraulic head, the drain spacing did not affect the soil moisture distribution. Subsurface irrigated plots were found to make better use of rain water than drained only plots since they did not permit the formation of well-defined pathways (macropores) allowing rainfall to move below the root zone without wetting it. It was also found that subsurface irrigation did not alter the soil structure appreciably and that autumn drainability was not affected in 1990 and 1991.

Persistent soil compaction by heavy-axle-load vehicles is a growing concern for the long-term productivity of clay soils. For optimum soil management, however, we must be able to evaluate adequately soil structural damages. This study compares different methods of assessing soil structure as affected by compaction and subsoiling treatments in a clay soil under corn production. / The tests used were: total porosity as calculated from densimeter readings and from soil cores; structural porosity; water desorption characteristics; and soil profile examination. These tests were performed in three layers of 20 cm and evaluation was based on their practicality and their ability to differentiate between treatments and to correlate with corn yield. / The results confirm that total porosity is a poor indicator of compaction in the subsoil. In soil profile assessments, ped descriptions were preferable to examination of pores. Water content and saturation deficit at $-$4.0 and $-$100 kPa were the best indicators of treatments and plant response.

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Due to the complex characteristics of tunneling problems, tunneling engineering is perhaps one of the areas in which numerical methods are more frequently adopted in practice. One important application is to examine the influence of an excavation and construction procedures on the stress distribution and deformation in the ground surrounding the opening and on the tunnel lining. Another important aspect of tunneling problems that can be accounted for in a numerical analysis is the complex geometry associated with typical applications. This is not only related to the shape of the opening, but also to the presence of non-homogenous or non-isotropic soil strata. / A constitutive model that is suitable for the analysis of structured clays has been developed in this study based on the multilaminate framework. The model takes into account the elastic unloading-reloading, inherent and induced anisotropy, destructuration and bonding effects. The model is implemented into Plaxis finite element program, successfully calibrated and used to investigate the response of structured sensitive clay to the construction of the Gatineau tunnel in Gatineau, Quebec and the Ottawa sewer tunnel in Ottawa, Ontario. Numerical results were compared to the field measurements taken during the tunnel construction. To improve the performance of the numerical model, an implicit integration algorithm is implemented and proven to be very effective as compared to the conventional explicit integration methods. The effect of different soil parameters including bonding and anisotropy on the tunneling induced displacements and lining stresses is also examined using a comprehensive parametric study. The results indicated that soil bonding and anisotropy have significant effects on the shape of the settlement trough as well as the magnitudes of surface displacements and lining stresses induced by tunneling.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 243-252.