Theses and Dissertations at Montana State University (MSU)
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Item Comparing the mechanical properties of shale cores: intact vs. fractured and sealed with UICP(Montana State University - Bozeman, College of Engineering, 2023) Bedey, Kayla Marjorie; Chairperson, Graduate Committee: Catherine Kirkland; This is a manuscript style paper that includes co-authored chapters.Fractures in subsurface shale formations are instrumental in the recovery of hydrocarbon resources. A result of hydraulic fracturing, these fractures have the potential to become harmful leakage pathways that may contribute undesired fluids to the atmosphere and functional groundwater aquifers. Ureolysis-induced calcium carbonate precipitation (UICP) is a biomineral solution where the urease enzyme converts urea and calcium into calcium carbonate mineral. The resulting biomineral can bridge gaps in fractured shale, reduce undesired fluid flow through leakage pathways, limit fracture propagation, better store carbon dioxide, and potentially extend the efficiency of future and existing wells. The mechanical properties of fractured shale sealed with UICP was investigated using a modified Brazilian indirect tensile strength test. Part one of this study investigated the tensile strength of shale rock using intact Eagle Ford (EF) and Wolfcamp (WC) shale cores (5.08 cm long by 2.54 cm diameter) tested at room temperature (RT) and 60°C. Results show no significant difference between shale types (average tensile strength = 6.19 MPa). EF cores displayed a higher strength at RT versus 60°C, but no difference was seen between temperatures for WC cores. Part two used UICP to seal shale cores (5.08 cm long by 2.54 cm diameter) with a single, heterogeneous fracture spanning the core length. UICP was delivered two ways: 1) the flow-through method injected 20-30 sequential patterns of microbes and UICP-promoting fluids into the fracture until fracture permeability reduced by three orders of magnitude and 2) the immersion method placed cores treated with guar gum and UICP-promoting solutions into a batch reactor, demonstrating that guar gum is a suitable inclusion to UICP-technology and may be capable of reducing the number of injections required in flow-through methodology. Tensile results for both flow-through and immersion methods were widely variable (0.15 - 8 MPa), and in some cores the biomineralized fracture split apart. Notably in other cores the biomineralized fracture remained intact, demonstrating more cohesion than the surrounding shale, indicating that UICP may produce a strong seal for subsurface application.Item Experimental evaluation of the mechanical properties of recycled high-density polyethylene (rHDPE) blended with talc filler, for engineering applications(Montana State University - Bozeman, College of Engineering, 2023) Malyuta, Daniel Aaron Isilyumu; Chairperson, Graduate Committee: Kirsten Matteson; This is a manuscript style paper that includes co-authored chapters.The extensive use of thermoplastic products, particularly high-density polyethylene (HDPE), has led to significant plastic waste, posing environmental threats. To manage thermoplastic waste, recycling is the preferred method; however, this has not been wholly effective due to technological and economic challenges and limitations. Large-scale applications of recycled HDPE (rHDPE) can incentivize recycling and create new revenue streams. HDPE is a well-established thermoplastic for engineering applications, and components made of HDPE have desirable properties such as high strength-to-weight ratio, ease of processing, availability, low cost, and excellent chemical and corrosion resistance. With concerns about the fate of plastics at end-of-life, there is a growing interest in strategies to utilize rHDPE in place of virgin HDPE (vHDPE). This study focused on investigating the mechanical and thermal properties of rHDPE-talc blends across various talc filler contents and temperatures, and across four recycling generations, as understanding these properties is crucial for application. Following ASTM standards, tests for tensile strength, elastic modulus, storage modulus, nominal yield stiffness, nominal yield strain, impact strength, and melt flow index were performed. Dynamic mechanical analysis and differential scanning calorimetry were also carried out. Results show that talc content and temperature affect tensile strength, elastic modulus, nominal stiffness, yield strain, impact strength, and storage modulus. Melting temperature decreased while crystallinity increased with talc filler content increase. Compared to neat HDPE and in most cases vHDPE-talc blends, rHDPE-talc blends perform better. Response Surface Methodology was applied using the Central Composite Design statistical experimental design approach to further study the stiffness and strength of rHDPE as functions of temperature and talc filler content. It revealed significant correlations for practical applications. Increasing the number of thermal reprocessing cycles decreased tensile strength, elastic modulus, impact strength, and storage modulus, while nominal yield strain and melt flow index increased. Crystallinity and melting temperature minimally decreased with increased thermal reprocessing cycles. Despite these changes, most of the properties of both the neat rHDPE and its talc blends remain comparable to the virgin counterparts, even after the fourth recycling generation. This implies that the recycled materials can be suitable for use in existing applications of vHDPE.Item Evaluation of transverse behavior of geosynthetics when used for subgrade stabilization(Montana State University - Bozeman, College of Engineering, 2013) Morris, Zachary Lee; Chairperson, Graduate Committee: Steven PerkinsState departments of transportation (DOTs) routinely use geogrids and geotextiles for subgrade stabilization. There is a general consensus between state DOTs concerning the effectiveness of these geosynthetics for this application; however, there is a lack of understanding and agreement with respect to the material properties of the geosynthetics that most directly relate to performance. A full-scale field study using geosynthetics as subgrade stabilization was conducted to analyze the performance and transverse behavior of 14 reinforced test sections under vehicular loads. Insight into the mechanisms of support that geosynthetics provide was determined based on strain gage and LVDT measurements, and transverse rut profiles. Mechanical properties of geosynthetics were compared to truck passes at the transition from lateral confinement to membrane support as well as at failure to evaluate which properties best predicted field performance. The properties evaluated included wide-width tensile strength, cyclic tensile modulus, resilient interface shear stiffness, junction strength, and aperture stability modulus. The behavior of geosynthetics was primarily characterized by when they started to transition from lateral confinement to membrane support. The results indicate that in general, the geosynthetics transitioned between truck pass 80 to 300 at a corresponding average elevation rut of about 1.7 inches, or between 1.7 to 3.1 inches of apparent rut. Failure was defined as 3 inches of elevation rut, and in general, the geosynthetics that transitioned to membrane support before truck pass 80 to 300 failed early. The results from the field study indicate that junction strength and stiffness, and wide-width tensile strength at 2% and 5% strain may be the most pertinent mechanical properties of geogrids, and surface friction may be the most pertinent property of geotextiles, for estimating field performance when used for subgrade stabilization applications with 10 to 12 inches of base aggregate, CBR strength values between 1.5 to 2.2, and elevation ruts less than 3.0 inches (or less than 5.4 inches of apparent rut).