Browsing by Author "Scalia, Joseph, advisor"
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Item 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 memberSoil 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.Item Embargo Development and characterization of solid-state, internet of things-based pH sensors for in-situ monitoring of soil and groundwater(Colorado State University. Libraries, 2022) VanTilburg, Charles Henry, IV, author; Scalia, Joseph, advisor; Sale, Thomas, advisor; Ham, Jay, committee memberHerein I test and examine a new solid state pH sensor design for use in soils and groundwater monitoring. The concept presented here is intended to expand the capabilities for monitoring geochemical parameters in the subsurface by combining a durable, solid-state pH sensor for subsurface deployment with an automated 'internet of things' (IoT) based pH meter that allows the collection of near-real-time continuous data streams for monitoring biogeochemical processes in hydrologic systems. Tests performed in this work were intended to provide a benchmark for further refinement of the design and yielded promising results, including hydrogeologically useful response times (on the order of hours), durability (stresses >1,000 kPa), and reproducible behaviors with multiple sensors. These results support that this technology is promising for future work. The pH sensor design combines a titanium mixed-metal-oxide electrode (TiMMO), solid epoxy body, and a proton-selective Nafion™ ionomer coating to yield a durable solid-state sensor that is sensitive to aqueous proton activities. As the sensor is exposed to water, the diffusion of aqueous protons through the selective Nafion™ coating causes an increase in voltage on the electrode as compared to a reference electrode. The Nafion™ coating reduces the influence of other ions in the system, creating a proton selective sensor. Because of the durable solid-state construction, the sensor can likely be deployed in-situ in challenging environments such as in soils where common glass pH sensors are too fragile for use. This unique advantage allows the pursuit of new biogeochemical monitoring strategies that leverage a high volume of discrete in-situ measurements for near-real-time continuous datastreams. This new strategy, powered by IoT systems, can integrate with smart networks of multiple components and generate large amounts of data for use in artificial intelligence and machine learning systems while also providing insight into processes that occur at smaller spatial and temporal scales than those understood with current subsurface monitoring strategies. pH is a master variable in aqueous and soil chemistry, both an indicator and controller of most chemical reactions and many physical processes that take place in soil and groundwater. pH is important for understanding chemical speciation, mobility, and stability in the soil, while also influencing soil physical properties like soil structure. pH is a parameter of interest to many industries and fields of study including, but not limited to, agriculture, mining, water resources, and engineering. As this work was intended to be a first approximation for studying this technology, multiple promising results and points of improvement were discovered. This work identifies a clear voltage response by the sensor to pH changes (-29 mV/pH) while also demonstrating the change behavior during stepwise pH changes to be approximately logarithmic (Δvolt=3.85ln[t], where Δvolt is the change in millivolts and t is time in minutes). Furthermore, this work demonstrated that these sensors can be used with an IoT monitoring system in the intended application. However, more work is needed to remove variability in the data, explore further designs and processes for coating and treating the sensors, analyze the long-term use, drift, and standardization of the sensors, and employ the data in analytics. Future work should include further lab testing to compare alternative design features and to evaluate stressors such as non-target ions and dehydration. After refinement in the lab, the sensors should be installed in pilot scale studies and in the field to evaluate their performance in real world conditions.Item Open Access Estimating interstitial discharge and velocity in flow in riprap and gabion engineering applications(Colorado State University. Libraries, 2019) Keene, Anthony, author; Thornton, Christopher, advisor; Scalia, Joseph, advisor; Williams, John, committee memberInterstitial flow is a difficult hydraulic process to measure and predict. Interstitial flow does not follow the same laws as seepage flow in small-grain media (i.e. Darcy's Law), because flow regimes in aggregate rock are often transitional or turbulent at a mild slope. Flow paths and local velocities in open cavities of a rock layer are dynamic, and instrumentation is difficult to place in rock for physical measurement. Due to the dynamic and complicated nature of interstitial flow, limited tools are available for engineering flow through aggregate rock. Flow in aggregate rock is relevant to many hydraulic engineering applications, including riprap and gabions used in designs for drainage, earth retention, and rockfill structures. Riprap and gabion published design guidelines are derived from external flow conditions and often neglect interstitial flow. Discharge in rock directly influences internal forces that can transport loose rock or strain a gabion mattress structure, interstitial velocity also directly influences bed shear stress. However, despite the importance of interstitial velocity and discharge for design, riprap and gabion design guidelines are developed primarily for rock stability. There is a need for interstitial discharge as design criteria; estimating the discharge capacity of aggregate rock can be useful in applications where drainage for a design flow is relevant. Data from laboratory prototype gabion mattress tests are used in tandem with data collected in a previous study on riprap to develop two simple design equations to predict interstitial velocity and interstitial discharge per unit area of a rock layer. A multivariate nonlinear regression was performed as a function of the following key parameters in a rock system: rock size for which 50% of rock is finer than, D₅₀, rock size for which 10% of rock is finer than, D₁₀, coefficient of uniformity (D₆₀/D₁₀), acceleration due to gravity, and bed slope. The regressions yield a coefficient of determination of 0.97 for both interstitial velocity and interstitial discharge predictive equations. Equations are suited for use in rock layers with nominal sizes from ¼-in to 5-in on bed slopes up to 0.15 ft/ft.Item Open Access Hydraulic and chemical properties of geosynthetic clay liners in mining applications(Colorado State University. Libraries, 2017) Conzelmann, Joel, author; Scalia, Joseph, advisor; Shackelford, Charles, committee member; Sutton, Sally, committee memberGeosynthetic clay liners (GCLs) are thin (< 10 mm) factory manufactured hydraulic barriers used in environmental containment systems because of the propensity of bentonite to swell and immobilize water which results in low hydraulic conductivity, k (≤ 2-3×10-11 m/s). GCLs consist of bentonite (clay) bonded or sandwiched between layer(s) of geotextile and/or geomembrane. The effectiveness of GCLs in containment applications has been demonstrated for systems with low ionic strength solutions and leachates, such as municipal solid waste leachates. Increasingly, GCLs are being used in mining applications; these applications require further research and laboratory testing to demonstrate barrier effectiveness. Existing standard test methods are not well suited for testing of mine-waste-leachates; simple procedures to collect effluent for analysis are lacking, commercially available testing equipment is typically incompatible with extreme pH solutions often encountered, and the use of backpressure is recommended requiring testing at elevated pressures. To overcome these limitations, an alternative gravity method without backpressure, paired with a permeameter constructed from non-reactive materials and intended to minimize clogging was used. Validation of the gravity method is demonstrated through k and hydration testing with synthetic mine waste leachates and comparative tests performed by a standard method. Tests results support that GCLs attain saturation, and that the gravity method does not exhibit uncharacteristically low k due to unsaturated conditions. However, the gravity method revealed the possibility of preferential flow through fiber bundles for GCLs with higher degrees of needle punching which was not observed in standard method tests. The cause of the discrepancy between the two methods is hypothesized to be associated with applying backpressure in the standard method, indicating that the standard method may provide an un-conservative estimate of k for higher peel strength GCLs. Regardless, bentonite saturation is shown to occur without backpressure under conditions typical of k testing, illustrating that saturated (maximum k) tests can be achieved without backpressure. The k of GCLs to synthetic mine leachate solutions was tested using the gravity method with the chemical-resistant permeameter. Three different mine waste leachates are investigated, a neutral pH synthetic gold mining process solution, a high pH synthetic bauxite mining process solution, and a low pH synthetic copper mining process solution. Three different GCL products were also investigated, two higher peel strength GCLs (2170 N/m and 3500 N/m), and a standard peel strength GCL (700 N/m). The preliminary results of k testing are reported.Item Embargo Improving soil property predictions for applications in tailings and terramechanics(Colorado State University. Libraries, 2024) Bindner, Joseph R., author; Scalia, Joseph, advisor; Atadero, Rebecca, advisor; Bareither, Christopher, committee member; Niemann, Jeffrey, committee member; Ham, Jay, committee memberSoil properties are used by engineers and scientists to better understand the state and behavior of soils. For example, soil properties can be used to estimate surficial soil strength for vehicle mobility models and can be used to better understand the engineering characteristics of mine waste (tailings) stored in tailings storage facilities. Soil and tailings properties often have high spatial variability and often require high resolution data for engineering analyses. Standard laboratory procedures are commonly used to determine soil properties but are often impractical for large spatial extents. While some existing soil data products provide estimates of surficial soil properties, the fidelity of soil data products is often poorly understood and insufficient for many applications. Additionally, some field tests used to estimate soil properties, such as the cone penetration test (CPT), rely on empirical correlations that cannot be used for some soils. There remains a need for procedures which improve the speed and accuracy of soil property estimates across large spatial extents. The objectives of this study are to (i) evaluate how surficial soil moisture and soil strength vary with soil and landscape attributes across a large spatial extent, (ii) explore the use of field-based hyperspectral sensing and machine learning for the prediction of surficial soil properties across a landscape, and (iii) assess the use of laboratory hyperspectral sensing and machine learning for the prediction of tailings properties for potential application in situ via direct push methods. Soil and landscape attributes were determined at sampling locations across a semi-arid foothills region and used to assess how soil moisture and soil strength vary with soil and landscape attributes. Then, hyperspectral data were captured at select sampling locations and used to train and assess the performance of a convolutional neural network (CNN) for the predictions of soil properties. Finally, a diverse tailings-hyperspectral dataset was prepared in the lab and used to train and assess a CNN to provide proof of concepts for prediction of material properties relevant to TSF stability analyses.Item Open Access Incorporating vehicle trails in soil moisture downscaling for mobility assessments in coarse grained soils(Colorado State University. Libraries, 2024) Proulx, Holly E., author; Niemann, Jeffrey D., advisor; Scalia, Joseph, advisor; Lynn, Stacy, committee memberFine resolution (10-30 m) soil moisture maps are critical for determining vehicle mobility in agricultural, forestry, recreational, and military applications. Microwave satellites provide soil moisture products, but the spatial resolutions of these products are too coarse for such applications. Soil moisture downscaling methods, such as the Equilibrium Moisture from Topography Plus Vegetation and Soil (EMT+VS) model, can downscale soil moisture to fine resolutions. However, the EMT+VS model (like most other downscaling models) does not explicitly consider vehicle trails, which may have different soil moisture than undisturbed landscape locations. The objective of this study is to generalize the EMT+VS model to explicitly estimate the soil moisture of trails. The generalized model incorporates two hypothesized effects of vehicle traffic on trails (reduced vegetation cover and reduced porosity). To evaluate the generalized model, porosity and soil moisture observations were collected across a study region in the foothills of the Colorado Front Range. Data were collected at paired trail and landscape locations as well as unpaired landscape locations on six dates in Summer 2023. On average, the porosity of the trail locations was 86% of the paired landscape locations. Soil moisture on trails was on average 73% to 88% of the moisture of the paired landscape locations. Including the vegetation and porosity adjustments in the EMT+VS model reduced the tendency of the model to overestimate the moisture on trails and improved the root mean squared errors.Item Open Access Influence of co-disposing oil and gas exploration and production waste and municipal solid waste on hydraulic conductivity(Colorado State University. Libraries, 2022) Karimi, Sajjad, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sharvelle, Sybil, committee member; von Fischer, Joe, committee memberThe most common method of municipal solid waste (MSW) disposal in the U.S. is still landfilling. Co-disposal of MSW with other non-MSWs in solid waste landfills requires engineering design to reduce the risks associated with the stability and functionality of solid waste landfills. Hydraulic conductivity is one of the engineering parameters required to assess the stability of a landfill. This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) to municipal solid waste (MSW) landfills on hydraulic behavior of mixed waste. Hydraulic conductivity of solid waste is a function of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods. A series of laboratory experiments were conducted to assess the impacts of these factors on the hydraulic conductivity of solid waste. Exploration and production waste was prepared to two moisture contents for laboratory testing: (i) as-received, which had a dry weight water content of 18%; and (ii) wet, which had a target moisture content of 32% to 36%. Wet E&PW prepared to the water content threshold represented the upper bound of water content for which the HMW met regulations for direct disposal in an MSW landfill. Hydraulic conductivity of the as-received E&PW measured in a large-scale permeameter decreased from 7.3×10-5 m/s to 1.1×10-8 m/s with an increase in vertical stress from 1 kPa to 394 kPa. The ks of as-received E&PW in small scale a small-scale permeameter reduced from 1.2×10-7 to 1×10-9 m/s with increasing stress to 50 kPa, and then ks stabilized at 7.5×10-10 m/s with increasing effective stress to 400 kPa. Although ks of the small-scale E&PW specimen was two to three orders-of-magnitude lower relative to the large-scale specimen as a function of vertical stress, the data align when evaluating ks as a function of dry unit weight. This indicated similar response of small-scale and large-scale specimens to hydraulic conductivity with respect to dry unit weight. The effects of E&PW hydration can be observed via the wet E&PW. The initial dry unit weight of the wet E&PW specimen was approximately 14 kN/m3, with a ks similar to the trend in ks versus dry unit weight for the as-received (dryer) E&PW specimen. However, ks of the wet E&PW specimen reduced two orders of magnitude (6.6×10-6 m/s to 5.4×10-9 m/s) as the effective vertical stress was increased to 17 kPa and dry unit weight increased to 15 kN/m3. Subsequently, ks of the wet E&PW decreased one order of magnitude to 2.8×10-10 m/s as vertical effective stress was increased from 17 kPa to 389 kPa. The ks of the wet E&PW specimen was two orders of magnitude lower than as-received E&PW under 394 kPa effective vertical stress. The overall trends for all E&PW mixture ratios for both the as-received and wet E&PW were similar, and exhibited an as-expected decrease in hydraulic conductivity with increasing vertical effective stress. Hydraulic conductivity for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3×10-5 m/s to 1×10-7 m/s under effective vertical stress ranged from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in ks to 1×10-8 m/s as vertical effective stress increased above 200 kPa. The lowest ks at each stress level was measured for MSW mixed with 80% wet E&PW. Findings from this study indicate that addition of an E&PW did not change the hydraulic behavior of MSW. Mixture of E&PW and MSW creates a waste matrix such that hydraulic behavior still is controlled by MSW components at low stresses (and low dry densities). However, if vertical stress exceeds 50 kPa, mixtures of MSW + 80% (and above) E&PW were observed to produce a low permeability (i.e., ks < 1×10-9 m/s). If the E&PW is disposed in discrete layers without rigorous mixing with MSW, increasing vertical stress may substantially reduce the E&PW hydraulic conductivity producing water and vapor barriers within the landfill. These findings represent the specific E&PW tested in this study, however, when combined with other data in the literature, illustrate the need for establishing mixture ratio thresholds and intentionally co-disposing E&PWs.Item Open Access Internet of things monitoring of the oxidation reduction potential in an oleophilic bio-barrier(Colorado State University. Libraries, 2020) Hogan, Wesley W., author; Scalia, Joseph, advisor; Sale, Thomas, advisor; Ham, Jay, committee memberPetroleum hydrocarbons discharged to surface water at a groundwater-surface water interface (GSI) resulting in violations of the Clean Water Act often spark costly cleanup efforts. The oleophilic bio-barrier (OBB) has been shown to be effective in catching and retaining oils via an oleophilic (oil-loving) geocomposite and facilitating biodegradation through cyclic delivery of oxygen and nutrients via tidally driven water level fluctuations. Conventional resistive (e.g., geomembrane) or absorptive-only (e.g., organoclay) barriers for oil at GSIs limit oxygen diffusion into underlying sediments and are susceptible to overloading and bypass. Conversely, OBBs are designed to function as sustainable oil-degrading bioreactors. For an OBB to be effective, the barrier must maintain aerobic conditions created by tidally driven oxygen delivery. Oxidation reduction potential (ORP) sensors were installed within an OBB in the northeastern US with an internet of things (IoT) monitoring system to either confirm the sustained oxidizing conditions within the OBB, or to detect a problem within the OBB and trigger additional remedial action. Real-time ORP data revealed consistently aerobic oxidation-reduction (redox) conditions within the OBB with periods of slightly less oxidized redox conditions in response to precipitation. By interpreting ORP data in real time, we were able to verify that the OBB maintained the oxidizing conditions critical to the barrier functioning as an effective aerobic bioreactor to degrade potentially-sheen generating oils at GSIs. In addition, alternative oleophilic materials were tested to increase the range of candidate materials that may function as the oleophilic component of an OBB. Materials tested included thin black (232 g/m2), thin white (244 g/m2), medium black (380 g/m2), and thick black (1055 g/m2) geotextiles, as well as a coconut fiber coir mat. Finally, a model was developed to estimate the required sorptive capacity of the oleophilic component of an OBB based on site-specific conditions, which can be used to inform OBB design.Item Open Access Mechanisms of interaction between bentonite and anionic polymers in enhanced geosynthetic clay liners(Colorado State University. Libraries, 2021) Norris, Anna, author; Scalia, Joseph, advisor; Shackelford, Charles, advisor; Borch, Thomas, committee member; Benson, Craig, committee member; Bailey, Travis, committee memberPolymer enhanced bentonites (EBs) are a potential solution to the chemical incompatibility of natural bentonite in many containment applications. Relative to conventional (natural or un-enhanced) bentonites, EBs have shown improved (lower) hydraulic conductivity to high strength waste liquids, but the mechanisms underlying these improvements are not well understood. The EB geosynthetic clay liners (EB-GCLs) evaluated in this study were produced with linear anionic polymers poly(acrylic acid) (PA) and sodium carboxymethylcellulose (CMC), as well as a covalently crosslinked PA (PAx), using multiple mixing methods (dry-sprinkle, dry mix, and wet mix) and percent polymer enhancements (5-10% by mass). The results of hydraulic conductivity tests based on permeation with concentrated inorganic solutions, viz., 500 mM NaCl and 167 mM CaCl2, indicated that specific combinations of polymer type and mixing methods in the EB-GCLs produced a low hydraulic conductivity (≤ 5.0×10-11 m/s) for a given applied hydraulic gradient and permeant solution. The use of a lower hydraulic gradient (i.e., 30 vs. 300) also was shown to have the potential to yield a lower hydraulic conductivity of EB-GCLs, suggesting that EB-GCLs are sensitive to the applied hydraulic gradient in a way that conventional GCLs containing unamended sodium bentonite (NaB) are not. The reason for this difference is that there is less likelihood of any hydrogel existing within the EB-GCL being flushed from the EB-GCL at the lower hydraulic gradient. Batch adsorption tests were conducted with 16.7 and 167 mM CaCl2, 500 mM NaCl, 12.3 mM CaSO4 and 167 mM Na2SO4 solutions to compare the adsorption behavior with respect to cation and anion species and concentration. Poly (acrylic acid) adsorption onto NaB increased with increasing Ca2+ concentration (12.5 mM CaSO4 < 16.67 mM CaCl2 < 167 mM CaCl2), resulting in increasing solid (adsorbed) phase concentration of PA. Sodium bentonite tested with NaCl exhibited limited adsorption capacity for PA. Total carbon (TC) analysis was confirmed to be an accurate technique for measuring polymer loading of both as-prepared and hydrated/permeated EB-GCLs. A multiple lines of evidence approach was used to determine the mechanisms controlling the hydraulic conductivity of EB-GCLs. The results of the hydraulic conductivity testing were paired with measurements of polymer retention and qualitative measurements of hydrogel formation to understand the variables controlling polymer migration within and through the EB-GCL and the relationship between polymer retention and hydraulic conductivity. The results indicated that the low hydraulic conductivity of EB-GCLs (≤ 5.0×10-11 m/s) is controlled by a combination of pore blocking (mechanical entrapment) and adsorption of polymer hydrogel. The reduction in long-term hydraulic conductivity of EB-GCLs relative to unamended GCLs in aggressive inorganic solutions was determined to be the result of several factors, including (1) the formation of hydrogel, (2) the clogging of the largest (most conductive) pores by the hydrogel, (3) the balancing of seepage forces that are sufficient to mobilize the hydrogel into the pores but not sufficiently high to untangle and mobilize the hydrogel due to shear thinning or dislodging by inertial forces, and (4) the kinetics of hydrogel formation and adsorption of polymer to the surface of bentonite. This study illuminates the myriad of interconnected factors that can and must be optimized for EB-GCLs to provide effective long-term containment of aggressive inorganic wastes.Item Open Access Modeling and field evaluation of the strength of surface soils for vehicle mobility(Colorado State University. Libraries, 2019) Pauly, Matthew J., author; Scalia, Joseph, advisor; Niemann, Jeffrey D., advisor; Green, Timothy R., committee member; Butters, Gregory, committee memberSurficial soil strength is a critical variable in vehicle mobility and terrain trafficability analysis and varies substantially in time and space with soil moisture and texture. Fine-resolution (5-30 m grid cell) patterns of soil strength and soil moisture are necessary for routing of off-road vehicle operations and must be estimated for applications when direct measurement is too expensive, labor-intensive, or dangerous. Rating cone index (RCI) is the in-situ method typically used in mobility applications to empirically evaluate the strength of surficial soils. The RCI method provides one simple parameter to evaluate soil trafficability, but in doing so fails to separately characterize the various mechanisms (compressibility, stress independent shear strength, stress dependent shear strength) that govern soil behavior in relation to vehicle traffic. Alternatively, the Bekker soil strength framework, which encompasses pressure-sinkage and shear strength soil properties, offers a mechanics-based representation of soil behavior and has received increased interest from the terramechanics community in recent years. However, because RCI has been the focus of the terramechanics community over several decades, predictive relationships to estimate Bekker parameters using basic spatially- and temporally-variable input data (soil moisture and soil composition) do not exist. The objective of this study is to develop and evaluate a framework for prediction of Bekker parameters (cohesion and friction angle) as a function of soil moisture and soil texture (percentage of sand and clay). A model, termed the Strength of Surface Soils (STRESS) model, is introduced to estimate shear strength of surface soils using soil moisture, pedotransfer functions based on soil texture, and unsaturated soil mechanics. The STRESS model is paired with an existing soil moisture downscaling model, the Equilibrium Moisture from Topography, Vegetation, and Soil (EMT+VS) model. The pre-existing EMT+VS model includes two untested simplifications that make the model inconsistent with the STRESS model framework, so two previously neglected soil-related hydrologic considerations are introduced to the EMT+VS model: runoff and residual water content. The impacts of runoff and residual on soil moisture downscaling performance and spatial patterns of soil moisture are assessed at a test region in northeastern Colorado called Drake Farm with measured soil moisture data for model calibration and evaluation. The additions are successfully included in the EMT+VS model but the assumptions made in the pre-existing EMT+VS model are shown to be adequate for soil moisture downscaling. After assessing EMT+VS model additions, the STRESS model is applied to Drake Farm to produce spatial patterns of estimated friction angle and cohesion. Model estimates are compared to measured shear strength using a human-powered shear strength bevameter to evaluate the predictive capability of the STRESS model. The model is found to underpredict friction angle and overpredict cohesion at Drake Farm due in part to the use of class-average effective shear strength parameters that do not appear to adequately reflect the properties of surficial soils. Finally, the design and construction of two bevameters are summarized for field and laboratory measurement of Bekker parameters. The results of laboratory tests on the human-powered shear strength bevameter used in STRESS model evaluation are compared to traditional geotechnical strength testing to validate field-testing results and ensure repeatability of measurements. Additionally, the design and construction of a fully automated, laboratory-focused bevameter device with pressure-sinkage and shear strength testing capabilities are described, but this bevameter is not used for testing in this study.Item Open Access Predicting unsaturated soil strength for mobility assessments(Colorado State University. Libraries, 2023) Bullock, Matthew D., author; Scalia, Joseph, advisor; Niemann, Jeffrey D., advisor; Gallen, Sean, committee memberAccurate estimation of surficial soil moisture and soil strength is integral in the determination of vehicle mobility across landscapes for applications from agriculture to national defense. Especially important is the ability to estimate trafficability over large spatial extents at fine resolutions (10-30 m, or finer, grid cells). While methods exist to estimate soil strength across landscapes, these methods are empirical and rely on class average soil behavior or field measurements that are often difficult or impossible to acquire. In addition, modern terramechanics models require moisture-variable soil strength parameters (e.g., friction angle and cohesion) that cannot be easily acquired in the field. To tackle this issue, the Strength of Surficial Soils (STRESS) model was developed to estimate moisture-variable soil strength with a physics-based approach rooted in unsaturated soil mechanics. However, there has been a lack of field soil moisture and soil strength data from a spatially diverse landscape with which to evaluate the STRESS model. To test the STRESS model, a field study was conducted at the 4,000 ha Maxwell Ranch in the northern Colorado foothills. Soil moisture and soil strength were determined with HydraProbes and cone penetrometers, respectively, at 86 locations across the ranch on 10 dates from May to August 2022. The data were then used to test the STRESS model and determine if soil strength trends could be estimated from topographical and soil textural differences across the landscape. High variability was observed in soil strength measurements via field rating cone index (RCI) stemming from fine-scale terrain and soil features as well as variability in cone penetrometer use. Observed trends show lower soil strengths for greater soil moistures, steeper slopes, higher vegetation, and lower soil fines content. The STRESS model was able to estimate field RCI values with a mean relative error of 37.5%, while a pre-existing model had a mean relative error of 47.4%. The STRESS model was able to reproduce strength trends with fines content but failed to reproduce vegetation and topographical trends. Thus, the STRESS model outperforms the current RCI prediction method, but the uncertainty in the predictions remains large.Item Open Access Proposed laboratory investigation into electroosmotic dewatering of mine tailings(Colorado State University. Libraries, 2020) Vander Vis, Kimberly Ann, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sanford, William, committee memberGeotechnical concerns of tailings storage facilities (TSFs) often depend on the water content of the tailings. Tailings with low hydraulic conductivity often have high-water contents with low undrained shear strength at the time of mine closure which limits the ability to close the TSF. The purpose of this study is to explore undrained shear strength gain in surficial mine tailings using electroosmotic dewatering (EOD) to help promote closure and reclamation of TSFs. Electroosmotic dewatering uses electrodes to apply an electrical direct current to induce flow through a porous medium. An experiment was developed to assess the effectiveness of dewatering methods at bench-scale to increase undrained shear strength of tailings via three different methods: EOD, surcharge consolidation, and evaporation only. The proposed research will evaluate if EOD (1) increases undrained shear strength of saturated surficial mine tailings more rapidly and (2) increases undrained shear strength as a function of depth more effectively, compared to the other techniques. Factors that influence EOD were preliminarily evaluated and include electrodes used, pore fluid chemistry, degree of saturation, voltage gradient and electrode configuration. Additionally, electroosmotic dewatering of mine tailings has not been implemented on a large-scale possibly due to lack of developed procedure, difficult water removal, and lack of a commercially available EOD unit. A goal of the proposed research plan is to develop field-scale implementation methods and water removal techniques via a moisture wicking synthetic capillary drain unit to be coupled with electroosmotic dewatering (i.e., EO-Plant) for field-scale applications.Item Open Access Seepage-induced consolidation test mine tailings(Colorado State University. Libraries, 2017) Tian, Zhengguang, author; Bareither, Christopher A., advisor; Scalia, Joseph, advisor; Bailey, Travis S., committee memberThe objectives of this research were to design, construct, and evaluated the seepage induced consolidation testing (SICT) apparatus. Design of the SICT apparatus was based on existing apparatus at the University of Colorado-Boulder and University of British Columbia. Three materials were evaluated by the SICT and the odometer test to validate apparatus functionality: kaolin clay, fine synthetic tailings (FST), and average synthetic tailings (AST). This study consisted of the following tasks: (i) design and construction of the SICT apparatus; (ii) evaluation of geotechnical characteristics of kaolin clay, FST, and AST; (iii) conducting SICTs on kaolin clay, FST, and AST to determine the compressibility and hydraulic conductivity constitutive relationships; (iv) evaluation and comparison of the constitutive relationships of these materials with two constitutive models based on data from SICT; (v) conducting odometer tests on the same three materials to compare with results from the SICT; and (vi) evaluation of the effects of slurry composition on consolidation behavior (i.e., void ratio versus effective stress, e-σ', and hydraulic conductivity versus void ratio, k-e). The results of tasks i-vi support that the SICT apparatus constructed at Colorado State University (CSU) was reliable and repeatable based on benchmark tests conducted on kaolin clay. Constitutive relationship models generated from possible permutations of the seepage test and step loading test that comprise the SICT show a strong correlation. These models are compared to a composite model that combines all seepage and loading phases for a given SICT. The two models yield similar constitutive model parameters. Consolidation behavior (e-σ' and e-k) of kaolin clay, FST and AST show a wide range of behavior due to the different material grain size distributions.Item Open Access Shear strength of coal combustion product by vane shear(Colorado State University. Libraries, 2018) Herweynen, Wesley J., author; Bareither, Christopher A., advisor; Scalia, Joseph, advisor; Ridley, John, committee memberThe objective of this study was to evaluate the shear strength of a coal combustion product (CCP) using the vane shear test. The CCP was obtained from a CCP evaporation pond in the Eastern United States, and consisted primarily of silt-sized particles. A series of small-scale vane shear (diameter = 12.5 mm and height = 25 mm) and large-scale vane shear (diameter = 25 mm and height = 50 mm) tests were conducted on CCP. Undrained and drained strength envelopes were determined for CCP using consolidated undrained (CU) triaxial compression tests. Triaxial results were verified via consolidated drained (CD) direct shear tests on similarly prepared CCP specimens and comparing the results with the drained strength envelope. In addition, effects of the following variables on the vane shear strength of CCP were evaluated using the small-scale vane: (i) rate of vane rotation, (ii) time delay between vane insertion and beginning rotation (td), and (iii) elapsed time under the final vertical effective stress prior to shearing (tc). A fine synthetic tailing (FST), which was 100% fine grained with approximately 40% clay-sized particles, was evaluated for comparison via small-scale vane shear. FST was selected as the higher clay content and lower permeability, relative to CCP, made the material more suited for evaluating vane shear with undrained conditions. All test specimens were prepared in the laboratory via the slurry deposition method and consolidated to the target vertical effective stress. Vane shear strength results were compared to drained and undrained strength envelopes for CCP and FST. Vane shear strength results were represented in terms of peak shear strength and the initial horizontal effective stress acting on the vertical-oriented failure surface during vane shear. Vane shear tests on CCP in small-scale vane shear and large-scale vane shear yielded shear strengths that plotted between the drained and undrained strength envelopes. This was explained by the small diameter of the vane and/or high permeability of CCP that allowed drainage to occur during testing. Small-scale vane shear tests on FST yielded shear strengths comparable to the undrained strength envelope, which was justified by the considerably lower permeability of FST relative to CCP. Additional evaluation of small-scale vane shear tests on CCP revealed that rate of rotation and td had no influence on measured peak shear strength. This was attributed to the small vane size and high permeability of CCP, which allowed excess pore pressure to dissipate regardless of how fast the material was sheared. Diagenesis was observed to occur in CCP, whereby time-dependent chemical reactions lead to an increase in strength with time. In small-scale vane shear tests on CCP, peak strength was reached after approximately 72 hr. These vane shear tests that accounted for diagenesis (i.e., were allowed to remain under vertical stress for ≥ 72 hr) were found to be most comparable to the drained strength envelope identified via triaxial and direct shear testing. Thus, accurate measures of peak shear strength in CCP must account for diagenesis to occur.