<p> Unstable failure in underground mining occurs when a volume of material is loaded beyond its strength and displaces suddenly. It is recognized on various scales, from small rock bursts to the collapse of pillars or entire sections of a mine. The energy that is released during smaller scale events is manifested through the ejection of material, which can pose a hazard to the safety of miners. Larger scale events generate seismic waves as mine workings are damaged and may entrap miners or terminate production. </p><p> This dissertation focuses on the analysis of unstable failure in an underground room and pillar mining environment. The potential for violent pillar failure is assessed using numerical modeling techniques and a parametric approach to loading conditions and material strength properties. The magnitude of instability is quantified by calculating the release of kinetic energy that occurs as failure progresses in each simulation. </p><p> Fundamental mechanisms associated with the release of kinetic energy are analyzed in a series of finite difference models, and the results are compared with analytical solutions to illustrate the applicability of the energy calculations to increasingly complex modes of failure. Back analyses are performed on two room and pillar mine collapse events from the western United States by constructing large-scale models and reproducing widespread failure. The values of energy released in two-dimensional models are extrapolated by assuming a depth of failure in the third direction, and the total energy values are compared to the documented seismic magnitudes from each collapse through empirical equations. With further development of this numerical modeling approach, energy consideration may be used to study the potential for instability in a wide variety of mining excavations and identify the associated range of hazards.</p>

<p> A monitoring methodology is developed for investigating seepage and internal erosion in earthen dams with time-lapse measurements of self-potential anomalies associated with conservative salt and non-conservative heat tracer migration in the subsurface. The method allows for 1) detecting seepage zones in earthen dams and determining the preferential flow paths through seepage zones in a non-invasive manner from the ground surface, 2) monitoring the transient evolution of seepage path geometry, flow velocity, and permeability in real-time if high frequency measurements can be made, and 3) long-term non-invasive monitoring with wired or wireless sensors The method is first theoretically developed and tested in a laboratory using a conservative tracer, and then demonstrated at a 12 m high, 100 m long leaking earthen dam with complex, unknown seepage paths. The method is shown to be capable of rapidly detecting seepage zones discovered during a reconnaissance survey, and delineates the predominant seepage directions through the dam from the time-lapse self-potential anomalies. The time-lapse monitoring approach ensures improved spatial resolution, increased measurement frequencies, and improved data analysis capabilities relative to traditional approaches to seepage detection, and a cost-reduction for the application of this methodology is anticipated to follow advancements in wireless sensing and monitoring technologies. This method is designed to be a more cost-effective means of interrogating earthen dams and levees to answer questions such as: Is the dam safe? What are the geometries of the seepage zones inside of the dam, and over what spatial scale does anomalous seepage occur? What are preferential paths through the seepage zones? Is internal erosion actively occurring? At what rates are the geometries, permeabilities and flow rates of preferential seepage paths evolving?</p>

<p>The engineering characteristics of glacial tills in the Sierra Nevada are difficult to determine due to the depositional nature of the material; however, testing methods unique to these dense materials can be utilized to obtain good engineering data. A literature review was conducted to determine testing methods and recommendations for engineering in glacial till. Further literature review revealed a significant amount of glacial deposits mapped by the USGS and CGS in the Sierra Nevada geomorphic province in California. Sierra Nevada glacial till field and lab data were obtained from Taber Consultants along with samples for further testing. Consequently, four significant conclusions were determined from testing and research. First, it was determined that Sierra Nevada glacial deposits may have large amounts of clay due to neoformation of the local volcanic rockform. As a result, plasticity and compressibility results ranged from low to high. Second, SPT N values for matrix material were correlated with depth. Third, unconfined compressive strength results for coarse-grained samples with no cohesive binding were independent of depth. Fourth, the matrix material dominated the engineering behavior of a given glacial till layer. </p>

<p> The cause for low angle submarine landslide (SML) failures, at slope angles less than 4&deg;, currently cannot be readily predicted using conventional terrestrial sources (i.e. excess pore pressure, weak horizons). Numerous models that have been developed pertaining to mass wasting on continental margins generally fall into two categories: post landslide occurrence (Tsunami wave run-up modeling) on coast lines and core sample description on costal margins. To date, there has been limited research on determining bed failure depth of submarine landslides through modeling. We propose a new method of 2D numerical modeling of rupture surface within unconsolidated sediments using the &ldquo;Particle in Cell&rdquo; method in combination with a conservative finite volume scheme. The software is written in Python, using the Numerical Python (NumPy) library to reach compiled-code-like performance. The Particle in Cell method was tested for accuracy, advection, and numerical diffusion. A set of six numerical model simulations are presented in which we investigate the role of material and external properties (i.e. hydraulic diffusivity and sedimentation rate), and geometry in the quest to determine bed failure depth. Through initial modeling simulations, it is confirmed that yield strength, diffusivity and sediment loading all play a role in predicting failure.</p><p>

<p>The Sandia GeoModel is a continuum elastoplastic constitutive model which captures many features of the mechanical response for geological materials over a wide range of porosities and strain rates. Among the specific features incorporated into the formulation are a smooth compression cap, isotropic/kinematic hardening, nonlinear pressure dependence, strength differential effect, and rate sensitivity. This study attempts to provide enhancements regarding computational tractability, domain of applicability, and robustness of the model. A new functional form is presented for the yield and plastic potential functions. The model is also furnished with a smooth, elliptical tension cap to account for the tensile failure. This reformulation renders a more accurate, robust and efficient model as it eliminates spurious solutions attributed to the original form. In addition, this constitutive model is adopted in bifurcation analysis to track the inception of new localization and crack path propagation. For the post-localization regime, a cohesive-law fracture model, able to address mixed-model failure condition, is implemented to characterize the constitutive softening behavior on the surface of discontinuity. To capture propagating fracture, the Assumed Enhanced Strain (AES) method is invoked. Particular mathematical treatments are incorporated into the simulation concerning numerical efficiency and robustness issues. Finally, the aforementioned modified cap plasticity model is employed to investigate the nonlinear dynamic response of the earthen substructure of the rail. Studying the effects of high-speed trains on the track substructure.

<p>Petroleum is generated from finely grained source rocks rich in organic materials and accumulated and trapped in reservoir rocks with relatively higher permeability and porosity. Expulsion of petroleum through and out of source rocks is called primary migration. Primary migration, as a link between source rocks and carrier rocks, presents a vital challenge to the society of petroleum geosciences and exploration and attracts the research interests of many geologists and geochemists. Despite extensive research the effective mechanisms responsible for primary migration of hydrocarbons are still in intensive debate. </p><p> Conversion of kerogen to oil and/or gas results in appreciable volume increase due to the density difference between the precursor and the products. Overpressure is developed as a natural consequence in well-sealed dense source rocks at great depths. When the overpressure reaches some critical value, bedding-parallel microcracks are initiated owing to laminated structure and strength anisotropy of source rocks. As transformation proceeds, microcracks are driven to grow subcritically by the overpressure. Such microcracks serve as migration conduits for hydrocarbon flow and may connect to other preexisting conductive fractures to form fracture networks or systems, which may facilitate further migration of hydrocarbons. Convincing evidence from observations in nature and laboratory experiments is found to support the idea that microcracks caused mainly by overpressure buildup from hydrocarbon generation functions as effective primary migration pathways. Based on those published findings, the present dissertation adopted an integrated approach consisting of petroleum geochemistry, petrophysics and fracture mechanics to assess the role of self-propagating microfractures as an effective mechanism for primary migration of hydrocarbons. Four models were developed: migration though subcritical propagation and coalescence of collinear oil-filled cracks, migration through subcritical propagation of an oil-filled penny-shaped crack in isotropic source rocks, subcritical growth of a penny-shaped crack filled by hydrocarbon mix in anisotropic source rocks, and a penny-shaped crack driven by overpressure during conversion of oil to gas. To predict the migration time and quantities of oil and natural gas, we use the reaction kinetics taking into account of pressure and temperature histories during continuous burial of sediments. To account for the compressibility of gas at high temperatures and pressures, we adopt an equation of state for methane, the predominant component of natural gas. To address the excess pressure buildup through volume expansion associated with kerogen degradation and initiation of microfractures, we employ linear fracture mechanics. To simulate the propagation of microcracks, hence the migration of hydrocarbons, we use a finite difference approach. The time period for pressure build-up, the overpressure evolution over time, and crack propagation distance and duration are determined using the coupled model where the interaction of hydrocarbon generation and expulsion is included. A detailed systematic parametric study is carried out to investigate the sensitivity of hydrocarbon migration behavior to variations in the input parameters including elastic and fracture properties of source rocks, richness and type of organic matter and burial history. </p><p> Oil retained in the microfractures may be subjected to thermal cracking to form gas when the gas window is reached as the temperature and pressure continue to increase with the progressive burial. Numerical results are presented for the two cases: kerogen conversion to hydrocarbon mix and subsequently oil conversion to gas. The modeling results agree well with published geological observations which suggest that microfractures caused by overpressures mainly due to hydrocarbon generation serve as effective migration pathways for hydrocarbons within well-sealed source rocks under favorable burial conditions. The fully coupled multiphysics modeling allows us to gain some insight on the primary migration of hydrocarbons, which is essential for the exploration of source rocks. </p>

<p> Geothermal energy has the potential to become a substantially greater contributor to the U.S. energy market. An adequate investment in Enhanced Geothermal Systems (EGS) technology will be necessary in order to realize the potential of geothermal energy. This study presents an optimization of a waterbased Enhanced Geothermal System (EGS) modeled for AltaRock Energy&rsquo;s Newberry EGS Demonstration location. The optimization successfully integrates all three components of the geothermal system: (1) the present wellbore design, (2) the reservoir design, and (3) the surface plant design. </p><p> Since the Newberry EGS Demonstration will use an existing well (NWG 55-29), there is no optimization of the wellbore design, and the aim of the study for this component is to replicate the present wellbore conditions and design. An in-house wellbore model is used to accurately reflect the temperature and pressure changes that occur in the wellbore fluid and the surrounding casing, cement, and earth during injection and production. For the reservoir design, the existing conditions, such as temperature and pressure at depth and rock density, are incorporated into the model, and several design variables are investigated. The engineered reservoir is modeled using the reservoir simulator TOUGH2 while using the graphical interface PetraSim for visualization. Several fracture networks are investigated with the goal of determining which fracture network yields the greatest electrical output when optimized jointly with the surface plant. A topological optimization of the surface is completed to determine what type of power plant is best suited for this location, and a parametric optimization of the surface plant is completed to determine the optimal operating conditions. </p><p> The conditions present at the Newberry, Oregon EGS project site are the basis for this optimization. The subsurface conditions are favorable for the production of electricity from geothermal energy with rock temperatures exceeding 300&deg;C at a well depth of 3 km. This research was completed in collaboration with AltaRock Energy, which has provided our research group with data from the Newberry well. The purpose of this thesis is to determine the optimal conditions for operating an Enhanced Geothermal System for the production of electricity at Newberry. </p><p> It was determined that a fracture network consisting of five fractured zones carrying 15 kg/s of fluid is the best reservoir design out of those investigated in this study. Also, it was found that 100 m spacing between the fractured zones should be implemented as opposed to only 50 m of spacing. A double-flash steam power plant provides the best method of utilization of the geothermal fluid. For the maximum amount of electricity generation over the 30-year operating lifetime, the cyclone separator should operate at 205&deg;C and the flash vessel should operate at 125&deg;C.</p>

<p> Modified imbibition tests were performed on 69 subsurface samples from Monterey Formation reservoirs in the San Joaquin Valley to measure wettability variation as a result of composition and silica phase change. Contact angle tests were also performed on 6 chert samples from outcrop and 3 nearly pure mineral samples. Understanding wettability is important because it is a key factor in reservoir fluid distribution and movement, and its significance rises as porosity and permeability decrease and fluid interactions with reservoir grain surface area increase. Although the low permeability siliceous reservoirs of the Monterey Formation are economically important and prolific, a greater understanding of factors that alter their wettability will help better develop them. Imbibition results revealed a strong trend of decreased wettability to oil with increased detrital content in opal-CT phase samples. Opal-A phase samples exhibited less wettability to oil than both opal-CT and quartz phase samples of similar detrital content. </p><p> Subsurface reservoir samples from 3 oil fields were crushed to eliminate the effect of capillary pressure and cleansed of hydrocarbons to eliminate wettability alterations by asphaltene, then pressed into discs of controlled density. Powder discs were tested for wettability by dispensing a controlled volume of water and motor oil onto the surface and measuring the time required for each fluid to imbibe into the sample. The syringe and software of a CAM101 tensiometer were used to control the amount of fluid dispensed onto each sample, and imbibition completion times were determined by high-speed photography for water drops; oil drop imbibition was significantly slower and imbibition was timed and determined visually. Contact angle of water and oil drops on polished chert and mineral sample surfaces was determined by image analysis and the Young-Laplace equation. Oil imbibition was significantly slower with increased detrital composition and faster with increased silica content in opal-CT and quartz phase samples, implying decreased wettability to oil with increased detrital (clay) content. However, contact angle tests showed that opal-CT is more wetting to oil with increased detritus and results for oil on quartz-phase samples were inconsistent between different proxies for detritus over their very small compositional range. Water contact angle trends also showed inconsistent wetting trends compared to imbibition tests. We believe this is because the small range in bulk detrital composition between the "pure" samples used in contact angle tests was close to analytical error and because small-scale spatial compositional variability may be significant enough to effect wettability. These experiments show that compositional variables significantly affect wettability, outweighing the effect of silica phase.</p>

Thesis (Ph. D.)--Michigan Technological University, 2004. / One folded map in pocket. Includes bibliographical references. Also available on the World Wide Web.

With the increasing cost of land in the modern city it has been necessary to expand upward rather than on the surface. The result has been to concentrate commercial and industrial enterprises in small areas whose influence is felt over the entire world. Notable examples are New York and Chicago. In these developments the engineer has played no small part. It is claimed by some that the maximum economic height has been reached at a thousand feet. However, both the Chrysler and Empire State Buildings have slightly passed this mark. It is not improbable that even taller buildings then these will be built in the near future despite the prophesies to the contrary