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A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science (Geographical Information Sciences and Remote Sensing) Johannesburg, 2017 / Soil organic carbon is considered as the most determining indicator of soil fertility. The purpose of this research was to predict the soil organic carbon in the Mokhotlong region, eastern of Lesotho using in situ spectral measurements and random forest regression. Soil reflectance spectra were acquired by a portable field spectrometer. The performance of random forest regression was assessed by comparing it with one of the most popular models in spectroscopy, partial least square regression. Laboratory spectroscopy measurements of the soil samples were analysed for assessing the accuracy of in situ spectroscopy based-models. The effect of the Savitzky−Golay first derivative in improving partial least square regression and random forest regression in both spectral data was also assessed. The results indicated that the random forest regression could accurately predict the soil organic carbon contents on an independent dataset using in situ spectroscopy data (RPD = 3.77, Rp2= 0.88, RMSEP = 0.64%). The overall best predictive model was achieved with the derivative laboratory spectral data using random forest with the optimum number of key wavelengths (RPD = 3.77, Rp2= 0.88, RMSEP = 0.64%). In contrast, partial least square regression was likely to overfit the calibration dataset. Important wavelengths to predict soil organic contents were localised around the visible range (400-700 nm). An implication of this research is that soil organic carbon can accurately be estimated using derivative in situ spectroscopy measurements and random forest regression with key wavelengths. / MT 2017

This thesis examines the pre and post failure deformation behaviour of landslides in cut, fill and natural soil slopes, and of the deformation behaviour of embankment dams. The deformation behaviour of landslides and embankment dams have been analysed from a database of case studies from a number of classes of slope (and dam) and material type. The database included some 450 landslides in cuts, fills and natural slopes, and some 170 embankment dams. For landslides in soil slopes, methods and guidelines have been developed for use in the analysis, evaluation and prediction of the pre and post failure deformation behaviour. They take into consideration the factors influencing and the mechanics controlling the deformation behaviour for the classes of slope and material types, which are different for pre and post failure. Pre-failure deformations are largely controlled by the effective stress conditions within the slope, changes in the boundary conditions and the response of the soil to those changes in boundary conditions. Whether the soil, under the effective stress conditions imposed within the slope, is contractive (and saturated or near saturated) or dilative on shearing, has a significant influence on the pre failure deformation behaviour. The post failure deformation behaviour is strongly influenced by the mechanics of failure (including whether the soil is contractive or dilative on shearing), the source area slope angle, the downslope geometry, the orientation of the surface of rupture, the material properties and slide volume. Guidelines are presented for prediction of 'rapid' and 'slow' post failure velocity. For embankment dams, methods and guidelines have been developed for evaluation and prediction of the deformation behaviour during and post construction for selected embankment types. They take into consideration the influence of material type and placement methods, material strength and compressibility properties, embankment zoning geometry, embankment height, and reservoir operation, amongst other factors. Guidelines have been developed to assist in the identification of 'abnormal' deformation behaviour, which can be related to internal deformations or a marginal stability condition and the onset to failure.

Evaporation synergy is the phenomenon in which two porous medium textures that share a common vertical boundary experience a higher cumulative evaporation than either homogeneous texture can produce. Studies that have been conducted to date address this phenomenon in relatively fine and coarse sands but not in finer textured soils where viscous forces play a major role. The purpose of this study was to determine which of the 66 combinations of soil textures would exhibit evaporation synergy and develop a conceptual model of the conditions necessary for synergy. The numerical modeler HYDRUS was used to investigate all soil texture combinations and generate evaporation rates and cumulative evaporation amounts for each system. In addition, two combinations of soils were selected as laboratory experiments based on the HYDRUS predictions: one that exhibited synergy (Loamy Sand & Silt Loam) and one that did not (Loamy Sand & Sandy Clay). The laboratory data supported the HYDRUS predictions for evaporation synergy and non-synergy. The conditions necessary for evaporation synergy were developed from the numerical and physical models��� predictions and results. The two textures must experience different air-entry values to create lateral and vertical pressure gradients, the fine must possess a high enough hydraulic conductivity to allow water to move to its surface before it reaches its own air-entry value and possess the capillarity to maintain liquid film flow to its surface, and the viscous forces within the coarse must be low enough for water to be pulled from itself to the fine. It was also determined that the evaporation rate of a bi-texture decreases as a series of constant-rate steps until the fine enters S2 evaporation and is associated with a stepwise recession of the drying front in the coarse media. The duration of each step appears to be associated with the lateral distance from which water can be extracted within the coarse media. / Graduation date: 2013

Thesis (Ph.D.)--Rensselaer Polytechnic Institute, 1996. / Adviser: Ahmed-W. Elgamal. Includes bibliographical references.

Thesis (Ph.D.) -- University of Texas at Arlington, 2009.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S.)--Ohio State University, 1955. / Includes bibliographical references (leaves 41-42). Available online via OhioLINK's ETD Center

Thesis--M. Sc.(Eng.), University of Hong Kong. / Mimeographed.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy