Browsing by Author "Stright, Lisa, committee member"

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Open Access
A finite element analysis of flexible debris-flow barriers
(Colorado State University. Libraries, 2018) Debelak, Aliena Marie, author; Bareither, Christopher A., advisor; Mahmoud, Hussam N., committee member; Stright, Lisa, committee member
The objective of this study was to simulate the stress-displacement behavior of a flexible debris-flow mitigation structure with a three-dimensional finite element model (FEM). Flexible, steel ring-net structures are becoming state-of-practice for debris-flow mitigation in mountainous terrain. These structures have been shown effective in geohazard mitigation; however, design of these structures commonly does not incorporate coupled interactions between debris flow mechanics and stress-strain response of the steel structure Thus, this study focused on assessing the effectiveness of using a FEM model in ABAQUS to simulate coupled behavior encountered in a flexible debris-flow mitigation structure. The debris flow was modeled as a series of rectangular solid blocks and the flexible debris-flow barrier was modeled as a series of three individual parts – braking elements, cables, and rings. The primary model outputs evaluated were the temporal and spatial relationships of forces within the structure and final barrier deformation. A full-scale field experiment from literature was used as a benchmark test to validate FEM simulations, and subsequently the FEM was used to assess barrier sensitivity via a parametric study. Parameters were chosen to represent common geotechnical variables of the debris flow and structural variables of the steel, ring-net structure.
Open Access
Assessing the influence of model inputs on performance of the EMT+VS soil moisture downscaling model for a large foothills region in northern Colorado
(Colorado State University. Libraries, 2024) Fischer, Samantha C., author; Niemann, Jeffrey D., advisor; Scalia, Joseph, advisor; Stright, Lisa, committee member
Soil moisture is an important driving variable of the hydrologic cycle and a key consideration for decision-making in off-road vehicle mobility, crop modeling, drought forecasting, flood prediction, and a variety of other applications. Soil moisture can be estimated at coarse resolutions (>1 km) using satellite remote sensing or land surface models; however, coarse resolution estimates are unsuitable for many applications. Downscaling these products to finer resolutions (~10 m) creates soil moisture maps that are more useful. This study applies the Equilibrium Moisture from Topography, Vegetation, and Soil (EMT+VS) model to Maxwell Ranch, a 4,000-ha cattle ranch in Northern Colorado that represents a diverse range of topographic, vegetation, and soil characteristics and a wide range of soil moisture conditions. The EMT+VS model is a physically based geo-information method that downscales coarse resolution soil moisture estimates using ancillary fine resolution datasets of topography and vegetation. Input data to the EMT+VS model contain inherent sources of error that can impact the uncertainty of downscaled estimates. The objective of this study is to identify sources of uncertainty in inputs and assess their influence on the error of the EMT+VS model output. The study finds changes in vegetation input or digital elevation model (DEM) resolution introduce substantial errors in the EMT+VS model output; however, these errors can be mostly overcome when recalibration with local in-situ data is possible. The highest errors (RMSE = 0.20 cm3/cm3) tend to occur in locations with thick vegetation and high contributing area, which are difficult to accurately estimate with available remote sensing data sources.
Open Access
Effect of mixed-mode loading on fatigue and fracture assessment of a steel twin box-girder bridge
(Colorado State University. Libraries, 2019) Irfaee, Mazin M., author; Mahmoud, Hussam, advisor; Heyliger, Paul, committee member; Atadero, Rebecca, committee member; Stright, Lisa, committee member
Steel twin box-girders are considered an attractive option for the construction of bridges due to their basic design, simple form, and ease of creation. Despite their advantages, they are considered fracture critical and as such there is an additional mandate for these bridges to inspected more in depth. This causes their inspection cost to be approximately two to five times greater than that of bridges with non-fracture critical members. The required additional inspection in the U.S. is mainly driven by rare historical events of bridge collapse for bridges that were not steel twin box girders. In addition, the mandated additional inspection does not reflect the inherent level of redundancy in most bridges. Therefore, it is important to quantify the potential for fracture and the level of redundancy in steel two-girder bridges in general, and twin box girders in particular, to minimize their inspection cost. Recognizing the inherently large scatter in fatigue performance, evaluating crack propagation and potential for fracture should, however, be performed in a probabilistic manner using detailed models that represent accurate behavior of the bridge. In this study, a detailed numerical finite element model of steel twin tub-girder bridge is developed and crack growth analysis, potential for fracture of its main tubs, and its overall redundancy is evaluated. The crack growth analysis is performed using multi-mode linear elastic fracture mechanics while accounting for uncertainties in the random variables associated with crack propagation and fracture. The results of the crack growth analysis are utilized to develop fragility functions that specify inspection intervals versus probability of failure where failure is characterized by dynamic crack growth. The analysis conducted to quantify the potential for fracture show distinct possible failure modes that vary from brittle fracture to ductile fracture. The extreme loading case shows that the bridge overall is not at risk of collapse. It is important to note that this conclusion cannot be generalized for all tub girder bridges since the level of redundancy is expected to vary between bridges depending on many factors such as girders geometries, plate thickness, fabrication, among others. However, the presented approach and the corresponding results provide a systematic way by which fracture critical bridges can be evaluated.
Open Access
Evaluating spatial and temporal controls on recharge fluxes in a stream-alluvial-bedrock aquifer system
(Colorado State University. Libraries, 2023) Cognac, Kristen, author; Ronayne, Michael, advisor; Bailey, Ryan, committee member; Rathburn, Sara, committee member; Stright, Lisa, committee member
The dynamics and timescales associated with natural and induced recharge to aquifers dictate whether and for how long groundwater resources are sustainable. This dissertation contains three studies which apply groundwater flow and geostatistical modeling to evaluate spatial and temporal controls on recharge fluxes in a stream-alluvial-bedrock system. Each study is based on a recharge mechanism that occurs within the Denver Basin aquifer system, a regionally significant water supply for which long-term pumping and active aquifer depletion call for improved characterizations of recharge. While recharge is the theme of this dissertation, I don't attempt to directly estimate recharge for the Denver Basin, but rather to investigate and expose dynamics of recharge that are essential for accurate conceptualizations and estimates of recharge. The first study investigates controls and timescales associated with streambed fluxes which are an important component of seepage recharge along mountain-front streams. Streambed fluxes are highly variable through time and space, having a range of implications for stream-aquifer processes. While spatial variations in streambed flux have been heavily characterized, temporal variability has been limited to short-term or low-frequency measurements. This study calculates high-frequency time series of Darcy-based streambed fluxes over a three-year period using water level and temperature inputs from shallow (<1.5m) nested streambed piezometers installed in two mountain-front streams in Colorado, USA. Results reveal important conclusions about controls and patterns of temporal variability. Three predominant temporal scales of variability, sub-daily (<1day), daily (>1d; <1y), and interannual (>1y), are quantified through statistical measures. Sub-daily variability was related to ET, temperature-induced changes in hydraulic conductivity, and variable stream stage while daily variability was highly seasonal and related to specific events on the channel (e.g., beaver dams). The magnitude of sub-daily variability was significant compared to daily variability (ratio 0.03 to 0.7). Annual median fluxes at each site varied across years, but typically remained consistent in order of magnitude and direction. A strong linear correlation characterizes the relationship between the daily variability and the median annual flux at individual sites, highlighting how sites with greater fluxes also exhibit greater temporal variability. The temporal flux variations documented in this study have important implications for calculations and interpretations of hyporheic exchange and groundwater recharge. Results provide a basis for quantifying temporal variations in streambed fluxes and highlight the extent to which fluxes vary over multiple timescales. Chapters 3 and 4 are organized to progress vertically downward within the system to investigate controls for inter-aquifer exchange between the alluvial and bedrock aquifer, an important component of recharge to the underlying bedrock aquifer system. In Chapter 3, the potential for and controls of hydraulic disconnection between the alluvial and bedrock aquifer are investigated. Hydraulic disconnection occurs when unsaturated conditions develop between a stream and water table causing seepage rates to stabilize with additional water table drawdown. In this study, I demonstrate that hydraulic disconnection can occur between an alluvial and bedrock aquifer when unsaturated conditions develop between the two water tables and inter-aquifer flow rates stabilize with subsequent drawdown. Variably saturated flow modeling is performed to simulate the effects of drawdown on alluvium to bedrock flow rates (A-B flow). Bedrock aquifer heterogeneity is represented through object-based geostatistical models that are conditioned to wellbore data from the Denver Basin aquifer system. The Monte Carlo framework includes 200 heterogeneity realizations across a range of sandstone fractions. Results document the formation of unsaturated regions beneath the alluvium in all models, particularly where sandstone channels underlie thinner low-permeability mudstones. Three-dimensional heterogeneity creates complex saturation patterns that result in localized flow paths, spatially varying disconnection, and a gradual transition to hydraulic disconnection as the regional water table is lowered. Successive changes in A-B flow decrease over the course of simulations by 80% to 99% and final rates approach stability as indicated by changes of <1% between successive stress periods. Of the 200 models, 190 reach full hydraulic disconnection and 10 conclude with a transitional flow regime. Dynamic connectivity metrics developed within the study strongly explain flow results. I also evaluate the aspects of heterogeneity that are most likely to produce disconnection, highlighting several factors that influence disconnection potential. Chapter 4 evaluates the potential for a beaver dam to drive flow across the alluvial-bedrock contact. Beavers construct dams which promote a range of surface and near-surface hydrologic processes, however, the potential for beavers to influence deeper aquifer dynamics is less often, if ever, considered. In this study I consider the potential for a beaver dam, specifically increased stream stage and width upstream of a dam, to drive deeper flow from an alluvial to bedrock aquifer. I utilize a numerical groundwater flow model to simulate the effects of the beaver dam on inter-aquifer exchange rates. The base case model is parameterized based on observations from a beaver dam constructed on Cherry Creek in 2020 and the stream-alluvial-bedrock aquifer sequence in the Denver Basin in previous chapters. I also test whether the influence of the beaver dam is sensitive to the alluvial-bedrock contact depth, beaver pond depth, and hydraulic properties by simulating flow across a range of sensitivity scenarios. Model results document an increase in alluvial to bedrock flow on the order of 0.5% to 4%, depending on the contact depth, beaver pond depth, and hydraulic properties. Changes in hydraulic head due to the dam propagate deep into the aquifer (>30m), highlighting the potential for deeper aquifer impacts. The effect of the beaver dam is greatest for shallow alluvial-bedrock contact depths, deeper pond depths, and lower hydraulic conductivity contrasts between the alluvial and bedrock aquifer. Overall, results document the potential for beavers to influence deeper aquifer fluxes where regional hydraulic gradients are downward, highlighting broader potential for beaver dams to enhance aquifer recharge in deeper aquifer settings.
Open Access
Facies architecture and depositional processes influencing carbonate facies belt development along a low-inclined shelf, Huk Formation, Norway, and Komstad Formation, Sweden
(Colorado State University. Libraries, 2022) Van Hook, James J., author; Egenhoff, Sven, advisor; Stright, Lisa, committee member; Stanley, Michelle, committee member
Heterozoan, or temperate to cool water, carbonate successions can provide unique obstacles to establishing a typical depositional model that can be universally applied. Unlike their tropical realm counterparts, these carbonates are typically highly heterogeneous, occurring across a wide range of oceanographic and climatic settings, thus requiring a case-by-case approach to interpret any given depositional system. One such example is displayed in the Middle Ordovician aged Huk Formation of southern Norway, and Komstad Formation of Scania, Sweden. These formations are approximately 8m thick, corresponding to the Baltoscandian "Orthoceratite Limestone." This study aims to explore the depositional processes influencing the facies development along a temperate-water, low-inclined carbonate shelf environment by characterizing and interpreting two formations along the shelf profile representing varying positions along the transect. The Huk Formation consists of the lower Hukodden Member composed of mostly massive wackestone, a middle Lysaker Member composed of interbedded nodular to semi-nodular wackestone and carbonate mudstone, and an upper Svartodden Member composed of mostly massive packstone and some massive wackestone. The Komstad Formation is composed of an informal lower member, composed of mostly massive wackestone, and an informal upper member composed of interbedded nodular and semi-nodular wackestone and carbonate mudstone with some massive wackestone beds. The facies of these formations can be grouped into seven carbonate facies: massive trilobite- and brachiopod-bearing calcareous mudstone (facies 1), bioturbated carbonate mud-wackestone (facies 2), planar-bedded fossiliferous wackestone (facies 3a), nodular to lenticular fossiliferous wackestone (facies 3b), mud-rich carbonate wacke- to packstone (facies 3c), massive fossiliferous packstone (facies 4a), and fossiliferous carbonate packstone pockets (facies 4b). These facies are ordered by increasing grain size as well as relative grain biodiversity, reflecting an overall increase in energy regime and subsequent decrease in water depth. These facies are further interpreted to represent the various processes and facies development on a low-inclined carbonate shelf, with massive packstones and wackestones occupying the proximal middle shelf environment, thin beds of nodular to semi-nodular wackestone in the distal middle shelf, and carbonate mudstone in the deep shelf environment. Despite the overall decrease in energy regime at depth, the energetic influences on the carbonate facies changes indicate that storms had a prominent impact on their development throughout the succession. This along with the presence of bioturbation and burrowing throughout the succession indicate that even the distal most reaches of this succession was deposited above storm wave base in a well oxygenated and hospitable environment. These formations further reflect a relatively drastic sea-level fall compared to the over- and underlying dark graptolitic shales. Regional sea-level reconstructions identify a largely scale regression during the deposition of these carbonate successions relative to the overlying and underlying graptolitic siliciclastic mudstones, identifying a relative sea-level low point within the middle of the succession at the transition from the Volkhov to the Kunda stage. Paleoenvironmental and paleoclimatic reconstructions of Middle Ordovician Baltoscandia indicate that environmental conditions during this time were generally relatively stable, suggesting that the fine-scale interbedded wackestone and mudstone characteristic of these formations could serve as excellent indicators of the fine- scale climatic and environmental fluctuations.
Open Access
Facies distribution, its implications for climate signals, and hydrocarbon potential of the Permian Lyons Sandstone, Front Range Basin, northern Colorado, USA
(Colorado State University. Libraries, 2016) Kendigelen, Oguzhan, author; Egenhoff, Sven, advisor; Stright, Lisa, committee member; Omur-Ozbek, Pinar, committee member
The Permian Lyons Formation consists of mostly fine- to medium-grained sandstones with minor silt- and mudstone intercalations. The formation shows six siliciclastic facies that are grouped into two Facies Associations: Facies Association 1 consists of high-angle cross-laminated sandstones (Facies 1), low-inclined cross-laminated sandstones (Facies 2), horizontally-laminated sandstones (Facies 3), and chaotically-bedded to folded sandstones (Facies 4), while Facies Association 2 is mainly characterized by wavy- to irregularly-laminated silty sandstones (Facies 5) and massive to wavy-laminated silt-rich mudstones (Facies 6) with minor amounts of high-angle cross-laminated sandstones (Facies 1), low-inclined cross-laminated sandstones (Facies 2) and horizontally-laminated sandstones (Facies 3). Facies Association 1 deposits dominate the southern part of the study area whereas Facies Association 2 sediments are more common towards to north. Stratigraphically, Facies Association 1 and 2 deposits occur intercalated with each other, and generally show two time Facies Association 2 sediments overlain by Facies Association 1 deposits. This intercalation of Facies Associations is best observed in the central part of the study area. In the south, Facies Association 1 deposits strongly dominate the succession, and in the north Facies Association 2 deposits are much more common, and do not show intercalation clearly. In the Lyons Formation, high-angle cross-laminated sandstones (Facies 1) are interpreted as remnants of fossil eolian dunes. Between these dunes, nearly flat to low-inclined dry interdunal areas occur and they are characterized by low-inclined cross-laminated sandstones (Facies 2) and horizontally-laminated sandstones (Facies 3). Chaotically-bedded to folded sandstones (Facies 4) represent internal deformation of dune deposits in the lower portion of dune flanks. Deposition of wavy- to irregularly-laminated sandstones (Facies 5) reflects wet to damp conditions in interdune areas. Massive to wavy-laminated silt-rich mudstones (Facies 6) indicate the presence of small ponds or lakes between dunes. Facies Association 1 deposits overall represent dry eolian conditions, and Facies Association 2 deposits represent wet eolian conditions. The distribution of Facies Association therefore indicates that dry and wet climates were generally alternating but overall dry climate conditions dominated the southern part of the study area whereas wet conditions were more prevalent in the north. Stratigraphically, the north to south transect reflects an expansion of dry conditions northwards despite the climate fluctuations, and a “Goldilocks” window of where to best observe climate cycles in the central part of the study area. This change in depositional conditions is exclusively observed along a north-south transect but not evident in an east-west direction. This study interprets the parts of the succession where Facies Association 1 sediments dominate as the paleo-erg center, and the portions where wet Facies Association 2 deposits are more prevalent as a paleo-erg margin environment. In the Lyons Formation, dry eolian deposits show good reservoir quality because of overall excellent sorting and roundness of the grains, while wet eolian deposits contains more fine-grained sediment which causes poorly sorting and reduction of porosity. Therefore, this study interprets that the main Lyons Formation plays are in the southern part of the study area within the paleo-erg center where dry eolian deposits are strongly dominating.
Open Access
Modeling of wastewater volume from unconventional oil and gas fields in Wattenberg field, and evaluation of low salinity waterflood enhanced oil recovery on shale wells
(Colorado State University. Libraries, 2016) Bai, Bing, author; Carlson, Kenneth, advisor; Catton, Kimberly, committee member; Stright, Lisa, committee member; Omur-Ozbek, Pinar, committee member
Reuse of wastewater from hydraulic fracturing (flowback and produced water) is a sustainable option for wastewater management practice in unconventional oil and gas fields. Reuse reduces fresh water demand but also lowers the environmental footprint by reducing the storage and transportation of both fresh and wastewater. A successful reuse practice requires a thorough understanding of both the quantity and quality of the wastewater, and more importantly, its potential impacts on well performance. In the first part of this study, wastewater production models were developed for horizontal shale wells in Wattenberg field .In addition, a solid characterization and distribution analysis on wells fractured with fresh and recycled water was performed to understand their impacts on wastewater quality. The second part of this study focuses on understanding the mechanisms of low salinity waterflood (LSF) in unconventional shale wells, and how oil recovery is impacted by the total dissolved solids (TDS) of the recycled brine. Results from the studies above are summarized in Chapter 4 through Chapter 7. A framework for water production prediction was developed in Chapter 4. Water production models were developed with Arps equation for horizontal wells from five fields in Wattenberg field. For a better data fitting and modeling, three time periods were defined: Frac flowback, transition period and produced water. The frac flowback period is the first one month after production starts, followed with 5 months of the transition period and, thereafter, produced water period. A correlation was found between water production volume and locations of wells,; thus, location is very important for estimating water production. Additionally, wells with low gas-oil-ratio (GOR) tend to have higher water recovery. In Chapter 5, sources of variability in flowback and produced water volumes from horizontal oil and gas wells were identified from external factors (time, location, type of frac fluids, wellbore length, and water source).. Horizontal wells in the Denver-Julesburg basin operated by Noble Energy were studied and results show that water production varies with time, location and wellbore length.. Additionally, production volume variation with fracturing fluid type and water source (fresh versus recycled) was explored. Results indicate that both of these variables should also be considered when developing a general model for water production. A guar-based frac fluid resulted in greater water production when compared to a cellulose derivative-based fluid. Finally, wells fractured with a fresh water based fluid had significantly greater produced water volume than geospatially-paired wells with a 1/7-recycled/fresh blend based fluid. Chapter 6 provides a qualitative and quantitative characterization of solids in frac flowback and produced water from five horizontal wells at two separate sites in the Wattenberg field of Northern Colorado. The difference in solids from wells fractured with fresh water and recycled water is compared, and their distribution and characterization are identified by particle size distribution measurement and X-ray photoelectron spectroscopy (XPS). Results show that particle were smaller and more uniform in produced water samples collected during the first week of production from the wells fractured with recycled water, suggesting that the recycled water was more compatible with the shale formation and wells fractured with recycled water tend to clean out faster. Chapter 7 investigates two of the fundamental mechanisms of LSF, clay swelling and diffused double layer (DDL) expansion. Both mechanisms are impacted by the salinity/total dissolved solids (TDS) concentration of the injection water. To test these mechanisms, clay swelling tests and real-time contact angle measurements were performed in this study. Spontaneous imbibition was also conducted, with Niobrara shale core plugs from Denver-Julesburg Basin, to compare oil recovery from low salinity and high salinity brine. Results show an increase in oil recovery when the TDS of brine falls between 400 and 10,000 mg/L. These results also indicate that LSF improves oil recovery from unconventional shale formation, and therefore, an optimal TDS concentration exists for highest oil recovery.
Open Access
Natural frequencies of twisted cables: a numerical and experimental study
(Colorado State University. Libraries, 2021) Alkharisi, Mohammed K., author; Heyliger, Paul, advisor; van de Lindt, John, committee member; Chen, Suren, committee member; Stright, Lisa, committee member
As the uses of cables have increased in different engineering applications, a better understating of their mechanical and dynamical behavior becomes more critical. Over the past several decades, many analytical, experimental, and finite element models have been developed to investigate vibrations of the cable structure. This attention explains the importance of such a structure, where it is more challenging than many ordinary structures because of the nonlinearity of the geometry and other combined effects. In addition, the twist along cable length leads to coupling behavior on the various kinematic variables of the cable system. This work is aimed at predicting and investigating the natural frequencies and the translations and rotations mode shapes occurring stimulatingly for both horizontal and inclined sagged cables, using both numerical and experimental methods. An efficient numerical procedure using elasticity-based finite elements is presented to generate the primary elastic stiffness coefficients of single-layered six-wire strands where the cables are subjected to axial and torsional loads in three-dimensional space. Cable models with lay angles varying from 5 to 30 degrees are then compared to eight different one-dimensional analytical models for the same range of angles. The finite element model gives stiffness coefficients that are in good agreement with the analytical models for angles below the maximum angle of the cable. The free vibration behavior of untwisted and twisted cables is then analyzed using the derived stiffness and mass matrices. When discretized over the horizontal span, the sagged cable is represented using transformed axial, coupling, and torsional characteristics where the resulting two-node cable element has three translational and three rotational degrees of freedom. A similar computational approach is used for inclined cables using inclination angles from 10 to 60 degrees. The natural frequencies and modal shapes are found to be in very good agreement in comparison with the results obtained using extensive experimental tests for identical cable geometries and materials. Where a harmonically time-varying support motion is employed, undergo different conditions. The acceleration and angular velocity time histories are then collected by sensors mounted on the mid and quarter span of the cables. In addition to the experimental results, the frequency spectrum and the translational and rotational mode shapes are analyzed and compared with the limited analytical model available from the literature and the computer finite element software ABAQUS. Practical examples are used to demonstrate the validity and applicability of the finite element model for untwisted and twisted cables. Then, the influence of the principal and microstructural parameters variation on the dynamics of the cable is investigated. This study shows that the elasticity, twist coupling, initial sag, inclination angle, and self-weight of the cable play a considerable role in the frequency and modal coupling behavior. It further suggests that some of the simple models available may not be adequate to fully understand the significant levels of modal coupling in the cable's dynamic behavior. The methods used in this study are finally extended to experimentally find the internal damping ratios and the reduction in the in-plane peak motions when a damper is used.
Open Access
Paleozoic facies architecture in low-inclined mixed carbonate-siliciclastic sedimentary systems: depositional and tectonic signatures
(Colorado State University. Libraries, 2019) Novak, Aleksandra, author; Egenhoff, Sven, advisor; Stright, Lisa, committee member; Schutt, Derek, committee member; von Fischer, Joe, committee member
To view the abstract, please see the full text of the document.
Open Access
Rift to drift transition in the southwest Australian deepwater Mentelle Basin
(Colorado State University. Libraries, 2021) Guerzon, Emmanuel, author; Harry, Dennis, advisor; Stright, Lisa, committee member; Scalia, Joseph, IV, committee member
The Mentelle Basin is a deepwater polyphase basin located off of the southwest margin of Australia that formed during Late Jurassic and Early Cretaceous breakup of Gondwana. It is underlain by highly extended continental crust and is bordered to the west by less extended crust forming the Naturaliste Plateau, and to the east by the Yalingup Shelf and Perth Basin beneath the continental shelf and coastal plain. The purpose of this study is to characterize the depositional, subsidence, and tectonic histories of the Mentelle Basin during the syn-rift to post-rift transition period. We use seismic reflection data and boreholes drilled by the Deep Sea Drilling Project and International Ocean Discovery Program (IODP) to map three horizons and intermittent volcanic features within this > 134 Ma to 126 Ma period. The youngest horizon mapped was the top of Lithostratigraphic Unit 5 (LSU5) at IODP Site U1513, which corresponds with the lower Aptian age (126 Ma) when rifting on this part of the margin ended and seafloor spreading began between Greater India and Australia west of the Naturaliste Plateau. Also mapped was a reflector encountered at the top of the basalt pile in IODP Hole U1513D at the western edge of the Mentelle Basin. The oldest horizon mapped is the Valanginian Unconformity that lies below this basalt pile and corresponds with breakup and the onset of seafloor spreading on the Perth Abyssal Plain further north. Isochore maps and two depth structure maps generated from these horizons illustrate the subsidence history and structural and magmatic evolution of the Mentelle Basin during breakup. Syn-rift magmatism in the Mentelle Basin was more widespread than previously thought. While earlier studies deemed the western half of the Mentelle Basin magmatic, the eastern extent of magmatism was unknown. Seismic correlation of the basalt reflector at Site U1513 indicates the Naturaliste Plateau basalts extended eastward to the eastern flank of the Mentelle Basin. Younger flows 2 – 20 km wide and occasional volcanic cones ranging from 0.5 – 2.5 km wide are imaged in the western half of the basin to the toe of the eastern slope. These younger volcanic features were emplaced between the late Valanginian through the start of the Aptian age. Basalt flows and some volcanic features in the basin are interpreted to have been exposed and weathered at or above sea level around the time of emplacement before subsequent burial by a marine transgression. The Mentelle Basin began to subside prior to the Naturaliste Plateau (> 134 Ma) as rifting occurred between India and Australia-Antarctica. Once final breakup occurred and seafloor spreading began west of the Naturaliste Plateau, both the Mentelle Basin and Naturaliste Plateau subsided to bathyal depths beginning around 126 Ma.
Embargo
Shear and consolidation behavior of slurry-deposited, desiccated tailings and compacted filtered tailings
(Colorado State University. Libraries, 2024) Primus, Justin Michael, author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Stright, Lisa, committee member
The objective of this study was to (i) evaluate and compare the undrained shear behavior and (ii) the consolidation behavior of slurry-deposited and desiccated tailings versus compacted filtered tailings. In general, the evaluation supports the hypothesis that desiccation and resaturation of a hard rock mine tailings yield higher peak undrained shear strengths relative to compacted filtered tailings when considering similar initial conditions (e.g., stress and density). The increase in undrained shear strength was attributed to the tailings fabric, which generated a stiffer response to loading and transitional behavior from contractive to dilative tendencies when sheared undrained. Consolidated undrained (CU) triaxial compression tests were conducted on 64-mm-diameter specimens that followed two different procedures. Slurry-deposited tailings were desiccated to a target void ratio and water content, resaturated, and tested in isotropic, consolidated, undrained axial compression. Filtered tailings specimens were prepared to similar initial void ratios as those measured on desiccated tailings specimens and tested in triaxial compression in the same manner. One-dimensional consolidation tests were also conducted on desiccated and filtered tailings specimens in a similar sequence. The desiccated and filtered tailings exhibited contractive, strain-hardening behavior in the triaxial tests and yielded effective stress friction angles of 29.1° for the desiccated tailings and 27.7° for the filtered tailings. Desiccated tailings samples showed a stiffer initial peak deviatoric stress and slower decreasing rate of change in stress relative to the filtered tailings. There was no indication of a difference in stiffness or brittleness between tailings preparation methods. The higher shear strength of the desiccated tailings was attributed to (i) more pronounced inter-particle reinforcing effects and (ii) densification from stress-history of desiccation. One-dimensional consolidation tests yielded a trend of increasing preconsolidation pressure with decreasing initial void ratio for both the desiccated and filtered tailings. There were slightly higher average compression and recompression indexes computed for the desiccated tailings relative to the filtered tailings, providing an indication of the different in the fabric behaviors.