Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiii, 99 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references (p. 95-99).

"Thesis presented to the Faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the professional degree of Civil Engineer, Department of Civil Engineer, Department of Civil Engineering." / Bibliography: leaf [27].

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 50-51). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 50-51). Also available on the Internet.

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

Most models developed for hydraulic fracturing in unconsolidated sands are based on Linear Elastic Fracture Mechanics (LEFM) and tensile fracture (Mode I fracture). However, in unconsolidated sand formations the field data shows that LEFM based models cannot properly predict the fracture behavior. Hydraulic fracture lab experiments in a true triaxial setup which was made as a part of this study are designed to investigate the failure mechanism around the crack tip in unconsolidated sands and effects of fluid rheology, leak off, and stress state are investigated. The results show that two mechanisms of tensile and shear failure are involved in fracture propagation in unconsolidated sands and depending on the fracturing fluid rheology and stress state of the formation one or both of them can happen at the crack tip. Several experiments with different fracturing fluids, rates, and different stress boundary conditions are categorized into two major categories based on whether we have a fracture or not. A subsequent categorization is used to categorize the fractured cases into Tensile Failure, Shear Failure and Mixed Failure categories. First the experimental observations are presented and subsequently observations are analyzed and compared in order to explain the observations and conclusions. ;Tensile failure category is happening in medium viscosity fracturing fluids in the order of 20,000 cP viscosity at unit 1/s shear rate. Shear failure category is mostly taking place in low viscosity fluids (200 cP viscosity at unit 1/s shear rate). Mixed mode fracturing is happening in high viscosity fluids (70,000 cP viscosity at unit 1/s shear rate) with high stress anisotropy. However, the same fluid will give a No Fracture result in the case of isotropic or near isotropic stress state. It is shown that higher stress anisotropy increases the tendency of shear failure and at the same time, the resulting fracture will propagate in a preferential direction. However, tilting and branching might happen due to high stress anisotropy which is more pronounced in case of thicker fluids. It was also observed that in case of vaseline injection, stress anisotropy decreases treatment breakdown pressure. / text

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

Not available / text

Research into the financial management of construction plant and equipment maintenance is scant, despite the increased utilisation of mechanisation to augment productivity in recent years. This thesis addresses the shortage of meaningful research by developing a methodology for predicting the total average hourly maintenance costs of tracked hydraulic excavators operating in opencast mining. Initial pilot and field studies conducted revealed that maintenance management (in the form of record keeping and attitude to used oil analysis) within the plant hire and general construction industry was generally poor. Hence, the decision was made to focus the research upon plant operated by opencast mining contractors. Here, plant managers were found to utilise an optimum blend of predictive and fixed-time-to maintenance and also maintain a depth of machine history file data. Modelling total maintenance costs using multiple regression (MR) analysis at the five percent level of significance identified four key predictor variables. These were: machine weight; attitude to used oil analysis (regular use or not); type of industry (opencast coal or slate); and type of machine (backacter or front shovel). However, in order to determine the model's robustness an alternative modelling technique, namely artificial neural networks (ANN) was applied using the same variables identified as significant predictor variables in the regression analysis. Performance analysis conducted on the predictive power of both MR and ANN models revealed that overall the ANN model exhibited greater predictive performance. The thesis concludes with direction for future research and moreover, identifies the need for a more fastidious approach to maintenance management.

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