Mountain Scholar :: Browsing by Author "Bareither, Christopher A., advisor"

Browsing by Author "Bareither, Christopher A., advisor"

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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
A novel direct shear apparatus to evaluate internal shear strength of geosynthetic clay liners for mining applications
(Colorado State University. Libraries, 2016) Soleimanian, Mohammad R., author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Schaeffer, Steven L., committee member
The use of geosynthetic clay liners (GCLs) in engineering practice has grown extensively over the past three decades due to application of this material containment applications such non-hazardous solid waste, residential and commercial wastewater management, roadways, and other civil engineering construction projects. This growth has been supported by an enhanced understanding of the engineering properties of GCL as well as hydraulic and mechanical behavior for different applications. In particular, the internal shear strength of GCLs is an important design consideration since GCLs often are installed on sloped surfaces that induced internal shear and normal stresses. The objective of this study was to develop a direct shear testing apparatus to measure the internal shear strength of GCLs for use in mining applications. The direct shear apparatus was designed to support the following testing conditions for needle-punched reinforced GCLs: hydration and testing in non-standard solutions (e.g., pH ≤ 1 or pH ≥ 12); testing under high normal stresses (up to 2000 kPa); and testing at elevated temperatures (up to 80 °C). Ultra-high molecular weight polyethylene GCL shear boxes were developed to facilitate testing 300-mm-square and 150-mm-square specimens under displacement-controlled conditions. Experiments were conducted on 150-mm-square and 300-mm-square GCL specimens to (i) evaluate gripping surface effectiveness as a function of peel strength and normal stress, (ii) assess hydration procedures to adopt into a systematic shear-testing protocol, (iii) assess stress-displacement behavior for 150-mm and 300-mm GCL shear tests, and (iv) develop failure envelopes for peak shear strength (τp) and large-displacement (τld). Shear behavior and peak and large-displacement shear strengths measured on both 150-mm and 300-mm square GCL specimens compared favorably to one another as well as to data from a previous study on a similar GCL. These comparisons validated the direct shear apparatus developed in this study and support the use of small GCL test specimens to measure internal shear behavior and shear strength of reinforced GCLs. Furthermore, the pyramid-tooth gripping plates developed to transfer shear stress from the interfaces between geotextiles of the GCL and shear platens to the internal region of a GCL were effective for a needle-punched GCL with peel strength of 2170 N/m and at normal stress ≥ 100 kPa.
Open Access
Assessment of municipal solid waste settlement models based on field-scale data analysis
(Colorado State University. Libraries, 2014) Kwak, Seungbok, author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Hess, Ann M., committee member
An evaluation of municipal solid waste (MSW) settlement model performance and applicability was conducted based on analysis of two field-scale datasets: (1) Yolo and (2) Deer Track Bioreactor Experiment (DTBE). Yolo data were used to assess a multi-layer immediate settlement analysis and model applicability to represent compression behavior in conventional and bioreactor landfills. The DTBE included four waste layers constituting a composite waste thickness. Settlement data for each waste layer were simulated to assess variation in model parameters, and a composite waste settlement prediction was completed via applying average DTBE model parameters to each waste layer and summing settlement to represent measured settlement at the top of the waste column. The multi-layer immediate settlement analysis developed for Yolo provides a framework to estimate the initial waste thickness and waste thickness at end-of-immediate compression. An empirical estimate of the immediate compression ratio (Cc' = 0.23) combined with precompression stress (10 to 15 kPa) and recompression ratio = 1/10·Cc' yielded the target immediate settlement for the Yolo test cells. A precompression stress and recompression ratio may need to be included when using empirical estimates of Cc' to predict under small vertical stress (e.g., less than 15 kPa). Simulation of the Yolo test cells with all settlement models via least squares optimization yielded high coefficient of determinations (R2 > 0.83). However, empirical models (power creep, logarithmic, and hyperbolic) are not recommended for use in MSW settlement modeling due to non-representative long-term MSW behavior, limited physical significance of model parameters, and the requirement of measured data to determine model parameters. Settlement models that combine mechanical creep and biocompression into a single mathematical function (i.e., Gibson and Lo and Chen-2010) are formulated to constrain all time-dependent settlement to a single process with finite magnitude, which limits model applicability. Overall, all other models used in this analysis, which either have the capability to simulate complete MSW compression behavior (Sowers, Marques, Babu, Chen-2012) or where an immediate compression component can be added to the model (Gourc and Machado), were shown to provide accurate simulations and predictions of field-scale datasets. The Gourc model included the lowest number of total and optimized model parameters and yielded high statistical performance for the DTBE prediction (R2 = 0.99). The Gourc model was also found to be the most applicable and straightforward to implement and is recommended for use in practice. All other models that included unique functions for immediate compression, mechanical creep, and biocompression (Machado, Sowers, Marques, Babu, and Chen-2012) are capable of yielding satisfactory MSW simulations and predictions; however, additional model and/or model constraints are necessary for implementing these models.
Open Access
Development and verification of a miniature cone penetration test
(Colorado State University. Libraries, 2019) Kahramanoglu, Kubra, author; Bareither, Christopher A., advisor; Scalia, Joseph, committee member; Singleton, John, committee member
The objectives of this research were to design and validate a miniature cone penetration test (MCPT) system for testing fine-grained soils. The system included a commercially-available miniature piezocone and a 300-mm-diameter, rigid-wall, calibration chamber. Three different materials were used in this study: (i) Ottawa sand, (ii) fine synthetic tailings (FST), and (iii) coal combustion product (CCP). Ottawa sand was used to evaluate repeatability of the MCPT apparatus and verify results via comparison to literature. The FST was a mixture of kaolin clay and silica flour, whereas CCP was primarily sand and silt and collected from a coal ash impoundment in North America. These two materials were tested to assess undrained and drained shear behavior and compare with previously measured shear strength. Replicate MCPTs conducted on Ottawa sand at three different relative densities indicated that the MCPT was repeatable. The assessment of tip resistance and sleeve friction in the Ottawa sand MCPTs were used to identify a functional depth of penetration whereby the friction sleeve was fully mobilized. Values of tip resistance and sleeve friction obtained from the MCPT at these depths of penetration were taken as representative of the specimen and subsequently validated via comparison to literature. Pore water pressure developed during cone penetration in the Ottawa sand and CCP were similar and indicative of drained conditions, whereas large, positive pore pressures in the FST were indicative of undrained conditions. The undrained shear strength estimated from MCPTs on FST (13 and 35 kPa) compared favorably and had a good agreement with undrained shear strength from triaxial tests. The effective stress friction angle for CCP based on MCPT (28.7° and 30.4°) yielded a conservative estimate relative to a previously determined effective friction angle via triaxial testing (36°).
Open Access
Effect of tailings composition on the shear strength behavior of mine waste rock and tailings mixtures
(Colorado State University. Libraries, 2014) Jehring, Megan M., author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Sutton, Sally J., committee member
The objective of this study was to evaluate the effect of mine tailings composition on the shear behavior and shear strength of co-mixed mine waste rock and tailings (WR&T). Crushed gravel was used as a synthetic waste rock and mixed with four types of tailings: (1) fine-grained garnet, (2) coarse-grained garnet, (3) copper, and (4) soda ash. Co-mixed WR&T specimens were prepared to target mixture ratios of mass of waste rock to mass of tailings (R) such that tailings "just filled" inter-particle void space of the waste rock (Ropt) prepared at the maximum void ratio of waste rock alone. Triaxial compression tests were conducted on waste rock, tailings, and co-mixed specimens at effective confining stresses (σʹc) of approximately 5, 10, 20, and 40 kPa. Low σʹTcT were selected to assess performance of co-mixed WR&T in final earthen cover applications for waste containment facilities. Waste rock and co-mixed WR&T specimens were 150-mm in diameter by 300-mm tall, whereas tailings specimens were 38-mm in diameter by 76-mm tall. Waste rock was tested with drained and undrained conditions, whereas undrained conditions were used for tailings and co-mixed specimens to reduce testing duration. Shear strength of the WR&T mixtures was comparable to that of waste rock alone. The effective stress friction angle (φʹ) of waste rock was 41°, whereas φʹ of the tailings ranged from 34° (copper) to 41° (soda ash). The WR&T mixtures had an average φʹ = 40° for fine-garnet mixtures and 39° for coarse-garnet and copper mixtures, which are similar to waste rock alone and suggests that the waste rock skeleton controlled shear strength of these mixtures. The soda ash mixtures had a slightly lower φʹ of 38° compared to waste rock alone, which was attributed to clay-sized tailings particles lubricating contacts between waste rock particles. Shear behavior of co-mixed WR&T was controlled by the tailings fraction when tailings were composed of silt and mixed to a ratio of R < Ropt. Waste rock controlled shear behavior of co-mixed WR&T when tailings were composed of sand or clay and mixed to a ratio of R ≥ Ropt. At σʹTcT = 5 kPa, the waste rock was entirely dilative, and transitioned to entirely contractive behavior at σʹTcT = 40 kPa. In WR&T mixtures, potential contraction of the waste rock skeleton will transfer normal and shear stress to the tailings fraction within the waste rock void space. Thus, shear behavior of co-mixed WR&T specimens were dependent on composition of the tailings and the overall soil structure, which is a function of R. The actual R for fine-garnet, copper, and soda ash mixtures was lower than the target ratio (R < Ropt) and corresponded to higher tailings content. An increase in tailings content creates a soil structure where tailings exist between inter-particle waste rock contacts and cause waste rock particles to "float" in a tailings matrix. Shear behavior of this co-mixed WR&T structure was dependent on composition of the tailings. Fine-garnet and copper mixtures expressed stronger dilative tendencies compared to tailings alone at all σʹTcT, which was attributed to interlocking between waste rock and tailings particles. Soda ash tailings alone were purely contractive, and combining two contractive materials resulted in a contractive WR&T mixture. The coarse-garnet tailings alone expressed strong dilative tendencies for all σʹTcT, whereas coarse-garnet mixtures exhibited similar shear behavior to waste rock alone. The contractive tendencies of coarse-garnet mixtures was attributed to specimens prepared at R > Ropt, which likely prevented involvement of the tailings fraction in transferring normal and shear stresses. The equivalent granular void ratio (e*), based on the global void ratio (eg) and tailings content, accurately characterized the soil structure of co-mixed WR&T by accounting for the contribution of tailings particles in transferring stress. The equivalent granular state parameter (Ψ*), determined using e*, was able to capture the shear behavior of all waste mixtures. Shear strength behavior of co-mixed WR&T can be predicted using Ψ* provided R, eg, and the steady state line of the WR&T mixture are known.
Open Access
Effectiveness of polymer for mitigation of expansive soils
(Colorado State University. Libraries, 2017) Taher, Zana, author; Scalia, Joseph, IV, advisor; Bareither, Christopher A., advisor; Valdes-Vasquez, Rodolfo, committee member
The objective of this study was to determine the effectiveness of commercially available polymer treatment as a mitigation technique for expansive soils in transportation applications. Four commercially available polymers were used in this research. A survey of state departments of transportation within the mountain-plains region (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming) was conducted to define the state-of-the-practice in expansive soil mitigation. A literature review on expansive soil treatments, with a focus on polymer mitigation, was also performed to establish the state-of-the-art in expansive soil mitigation. The soil tested was composed of expansive soil from Fort Collins, Colorado, that classified as low swelling, amended with 15% (high swelling) sodium bentonite. Fifteen percent bentonite was selected to meet the Federal Highway Administration (FHWA) classification for highly expansive soil. Treated and untreated soils were classified, and tested for swelling, strength, and hydraulic conductivity. Four commercially available polymers were tested; lime and fly ash, two common techniques used in treatment of expansive soils, were tested for comparison. Preliminary swell tests were performed on four commercially available polymers, P1, P2, P3, and P4, to analyze the relative effectiveness of the polymers. P4 was selected for this study based on the high effectiveness of P4 from the swell test results. P4 reduced expansive soil swelling and increased strength, but was less effective than lime or fly ash. Based on reduced swelling, and increased strength, lime was the most effective treatment for stabilizing and strengthening the expansive soil tested. Swell test data do not support use of P4 (or P1, P2, P3) over traditional treatments for swell mitigation of the expansive soil tested in this study. However, lime and fly ash treatments resulted in multiple orders-of-magnitude increases in hydraulic conductivity, while P4 did not. Since water ingress is required for soil swelling, future testing that couples the effects of hydraulic conductivity and swelling is recommended. In addition, testing of other commercially available polymers, and additional soils (such as sulfate rich soils) is recommended.
Open Access
Hydraulic conductivity of fly ash-amended mine tailings
(Colorado State University. Libraries, 2016) Alhomair, Sultan A., author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Barbarick, Kenneth A., committee member
The objective of this study was to evaluate the effect of fly ash addition on hydraulic conductivity (k) of mine tailings. Fly ash-amended mine tailings have potential application as construction materials in active mines, transportation earthworks, and other geotechnical engineering projects. Addition of cementitious binder (fly ash) to mine tailings has the potential to reduce hydraulic conductivity and enhance contaminant sequestration to be feasible in earthwork projects. Mine tailings used in this study were categorized as synthetic tailings and natural tailings. Natural tailings were collected from a garnet mine located in the U.S. Two synthetic mine tailings were developed via blending commercially-available soils to create typical particle-size distributions and plasticity characteristics of actual mine tailings. The two types of fly ash used classified as off-specification, but had sufficient calcium oxide (CaO) content (17% and 18.9%) for pozzolanic activity. Hydraulic conductivity (k) was measured on pure tailings and fly ash-amended tailings in flexible-wall permeameters. All experiments were conducted following a constant head technique (Method A in ASTM D 5084). Fly ash was added to mine tailings to constitute 10% dry mass of the mixture, and specimens were cured for 7 and 28 d inside a constant humidity and temperature room (100% humidity and 21 ̊C) prior to hydraulic conductivity testing. Effluent from the experiments was measured for pH, electrical conductivity, and the presence of heavy metals to assess leaching potential of the tailings and fly ash-amended tailings mixtures. Chromium (Cr), copper (Cu), cadmium (Cd), and silver (Ag) concentrations were evaluated based on common heavy metals associated with fly ash and then compared with drinking water standards and toxicity limits. The influence of fly ash-amendment on k of mine tailings was attributed to (i) molding water content and (ii) plasticity of the mine tailings, or presence of clay particles. Average synthetic tailings that represent typical average particle-size distribution of tailings and natural tailings both classified as low-plasticity silts (ML) with clay contents less than 15%. Hydraulic conductivity of these fly ash-amended tailings were approximately equal to unamended tailings when prepared dry or near optimum water content (wopt), and two to five times lower than unamended tailings when prepared wet of wopt. Fine synthetic tailings that represent typical fine particle-size distribution of tailings classified as low-plasticity clay (CL) and contained 42% clay-sized particles, comprising primarily kaolin. The k of fine synthetic tailings increased approximately one order of magnitude with addition of fly ash for materials prepared dry or near wopt. This increase in k reduced to 3.4 times that of unamended tailings for material prepared wet of wopt. The increase in k with addition of fly ash for the clayey tailings was attributed to agglomeration of clay particles and an overall increase in average pore size to conduct flow. The decrease in k for silty tailings was attributed to formation of cementitious bonds between tailings particles that obstructed flow paths and decreased average pore size. The results also indicated that the effect of curing time on k is more pronounced during the early stages of curing (≤ 7 d), as there was negligible difference between k for 7- and 28-d cured specimens. The propensity to form cementitious bonds was evaluated via the CaO-to-SiO2 ratio, whereby fly ash with a higher CaO-to-SiO2 ratio was anticipated to yield lower k due to more cementitious bond formation. There was no distinguishable difference in the impact on k between the two fly ashes used in this study. Chemical constituents in the effluent of all hydraulic conductivity specimens were compared with literature on tailings-fly ash and soil-fly ash that have been used in geoengineering applications. Concentrations of Ag and Cd for all amended tailings were below the drinking water maximum contaminant levels (MCLs) and toxicity limits. This result was attributed to low solubility of Ag and Cd in alkaline environments (i.e., pH ≥ 7) combined with the propensity for Ag and Cd to sorb to solid particles. Concentrations of Cr and Cu for amended tailings with fly ash A (FA-A) exceeded drinking water MCLs and toxicity limits, which was attributed to low solubility and high mobility of Cr and Cu in alkaline environments. Thus, tailings amended with FA-A have potential use in transportation-related earthwork projects, but high initial concentrations of Cr and Cu must be evaluated. All tailings amended with fly ash A (FA-B) are an environmental-friendly option and can be safely used in transportation-related earthwork projects from an environmental perspective.
Open Access
Hydrologic comparison of prescriptive and water balance covers
(Colorado State University. Libraries, 2018) Stock, Caleb Swenson, author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Paschke, Mark W., committee member
The objective of this study was to compare the water balance of prescriptive and water balance cover (WBC) designs for Larimer County Landfill (LCL) via hydrologic modeling. A prescriptive cover is designed to limit percolation into underlying waste via a low permeability layer, whereas a WBC is designed to limit percolation via storing infiltrated precipitation and subsequently releasing the water through evaporation and transpiration. Guidance on WBC designs in Colorado are based on geographical location of the site and particle-size distribution of the available cover soils. Soil characteristics and engineering properties were determined from exhumed samples for a completed closure phase of LCL (Phase 1) and two borrow areas (Borrow Area 3 and Borrow Area 4). Hydrologic modeling was completed using VADOSE/W to predict the percolation rate through the prescriptive and water balance covers. The wettest ten consecutive years on record with a sufficiently complete meteorological data set (1992-2002) were selected for the analysis. Vegetation parameters were assigned to represent the revegetated state observed in Phase 1 and the natural conditions observed in the borrow areas. Predicted percolation through a prescriptive cover was < 0.1 to 2.2 mm/yr, depending on assumed saturated hydraulic conductivity. Evaporation was the primary process for removing water from the prescriptive cover models. Predicted percolation through the WBC models ranged from 6.3 to 11.3 mm/yr depending on the borrow area soil and vegetation parameters. Transpiration was the primary process for removing water from the WBC models. Within all of the regulatory acceptable cover models' evapotranspiration removed 94 to 102% of the precipitation received during the ten years modeled. Results of this study indicate that either a prescriptive cover with a total thickness of 106.7 cm (3.5 ft) or a WBC with a thickness of 76.2 cm (2.5 ft) will meet regulations for final closure cover at LCL.
Open Access
Implications of solid and liquid waste co-disposal on biodegradation and biochemical compatibility
(Colorado State University. Libraries, 2018) Cook, Emily M., author; Bareither, Christopher A., advisor; Sharvelle, Sybil E., advisor; Ippolito, James A., committee member
Co-disposal of solid and liquid waste in municipal solid waste (MSW) landfills can benefit landfill operations via enhancing waste moisture content and accelerating in situ waste biodegradation. However, implications of co-disposal on organic waste biodegradation are currently unknown and co-disposal in full-scale landfills is ad hoc. The objective of this study was to evaluate waste biodegradation and biochemical compatibility for different co-disposed solid and liquid wastes in MSW. To meet this objective, laboratory-scale reactors were operated to evaluate the potential impacts of co-disposal and ultimately to provide guidance for full-scale MSW landfill operations. Waste collected for this project was identified as MSW, special solid waste (SW), liquid waste (LW), and sludge waste (Sludge), such that reactor experiments were conducted with representative co-disposal combinations of MSW-SW, MSW-LW, and MSW-Sludge. The MSW-SW and MSW-Sludge reactors included landfill leachate as a liquid source to generate effluent; MSW-LW reactors were operated with unique liquid wastes. The MSW-LW reactors remained in the acid formation phase of biodegradation for the duration of the experiment. The liquid waste addition in the MSW-LW reactors was not an effective means to initiate biodegradation and is not recommended as an additive to fresh MSW without an inoculum that contains methanogenic microorganisms. All MSW-Sludge waste reactors and all but one set of the MSW-SW reactors reached methanogenesis. The solid and sludge wastes did not exhibit signs of biochemical incompatibility. The use of biochemical methane potential (BMP) assays as a selection tool for waste co-disposal was also evaluated. The BMP assays did not show good agreement with data from reactors that generated methane; therefore, use of BMP assays alone as a selection tool is not recommended.
Open Access
Laboratory evaluation of a post-fire ground treatment to mitigate soil erosion and runoff
(Colorado State University. Libraries, 2018) Moden, Kayla Nicole, author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Stevens-Rumann, Camille S., committee member
The objective of this study was to assess the efficacy of using agricultural straw mulch as a post-fire ground treatment to mitigate soil erosion and runoff. A laboratory research program was carried out to measure soil erosion and runoff in a physical slope-model experiment (surface dimensions = 76 cm long x 30 cm wide). Intact block samples were collected that represented conditions in Colorado wildfire prone areas. The vegetation on select block samples was burned to simulate a high-intensity wildfire. Unburned block samples with varying amounts of vegetation and burned block samples with varying amounts of straw mulch (0, 0.06, 0.11, and 0.22 kg/m2) were tested in the slope-model experiment at a slope of 28o under a simulated rainfall of 48 mm/h for 40 min. Burned block samples were exposed to two rainfall simulations conducted three days apart to explore changes in soil hydraulic properties due to potential soil crust formation. Runoff, and eroded sediment were collected during simulated rainfall, and intact subsamples were collected from unburned and burned block samples after the rainfall simulations to evaluate the effects of high severity burning on physical characteristics and hydraulic and mechanical properties (i.e., dry density, total organic carbon, hydraulic conductivity, water repellency, and shear strength). Burning exponentially increased erosion compared to unburned conditions and all rates of straw mulch reduced soil erosion to levels consistent with unburned samples. Runoff and erosion increased with a decrease in natural surface vegetation on unburned samples and increased with a decrease in straw mulch applied to burned samples. Notable changes in geotechnical properties with high severity burning were not found in this study, which suggested that the observed increase in erosion on bare burned samples during rainfall simulations was attributed to destruction of surface cover with burning.
Open Access
Landfill gas analysis to support an assessment of organic waste stability
(Colorado State University. Libraries, 2016) Mantell, Steven C., author; Bareither, Christopher A., advisor; von Fischer, Joe C., committee member; Sharvelle, Sybil E., committee member
Organic stability is defined as the state of near complete decomposition of organic waste constituents such that human health, environmental, and financial risks associated with undecomposed waste are reduced. An assessment of organic stability was completed based on comparison between collected and predicted landfill gas. There were two main objectives of the study: (i) assess landfill organic stability for an entire site and specific landfill phases to evaluate how operational practices influence organic stability and (ii) develop recommendations for conducting organic stability assessments based on gas collection and modeling. Landfill gas generation is frequently assessed on a site-wide basis; however, the process of waste disposal and subsequent gas generation varies temporally and spatially within a landfill. In this study, landfill gas modeling was conducted on a site-wide and phase-specific basis (i.e., multiple phases constitute the entire landfill site) for a non-hazardous solid waste landfill in the U.S. The U.S. EPA's LandGEM model for methane generation was used for the gas model simulations. LandGEM calculates the rate of methane generation based on the mass of solid waste, methane generation potential of the waste, and first-order rate coefficient (k). Models were completed that considered the following factors: (i) constant methane generation potential; (ii) methane flow rates representative of monthly and annual averages; (iii) collection efficiency of the landfill gas collection system; and (iv) optimization of k to reduce the sum of squared residuals between measured and predicted methane flow rates. Collection efficiency of the landfill gas collection system was accounted for in the models via assuming a constant collection efficiency of 85% and assuming a temporally varying collection efficiency. The temporally varying collection efficiency was used to represent temporal installation of a gas collection system and placement of interim and final cover. Site-wide decay rates varied from 0.068 to 0.070 1/yr while phase-specific rates varied from 0.021 to 0.12 1/yr. Observations reinforce previous studies showing that moisture enhancement has potential to create favorable landfill conditions that may lead to higher rates of methane generation and shorter durations to achieve organic stability.
Open Access
Mechanistic visco-elastic modeling of shear deformation and failure in internally-reinforced geosynthetic clay liners
(Colorado State University. Libraries, 2022) Baukus, Aaron, author; Bareither, Christopher A., advisor; Scalia, Joseph, committee member; Yourdkhani, Mostafa, committee member
Analysis and prediction of the shear behavior of a non-heat-treated needle punched geosynthetic clay liner (NHT NP GCL) have been conducted using a mechanistic model. A three-element Kelvin-chain model was employed to simulate the incremental loading of a rapid loading shear test. A performance analysis initially was conducted to evaluate variation in model parameters with respect to differences in physical properties of GCLs (i.e., peel strength) and experimental conditions (i.e., normal stress, temperature, creep shear stress). The optimized model parameters demonstrated sensitivity to the variation in internal and external factors and yielded empirical relationships that were carried forward to test model applicability for predicting time-to-failure for an internally-reinforced GCL. These data trends in combination with creep-test data were used to calibrate the creep deformation model. Time-to-failure predictions performed with the calibrated creep deformation model resulted in a percent error < 9%. A modified model-calibration procedure was developed to extend model applicability to stress conditions common in practice. The modified calibration procedure was used to predict NHT NP GCL creep deformation in a hypothetical landfill cover system. The time required for the projected deformation to surpass 3 mm exceeded one million years for all stress conditions evaluated, which suggested that the NHT NP GCL will not experience creep failure in the low-stress cover scenarios evaluated.
Open Access
Numerical evaluation of one-dimensional large-strain consolidation of mine tailings
(Colorado State University. Libraries, 2015) Agapito Tito, Luis Angel, author; Bareither, Christopher A., advisor; Shackelford, Charles D., advisor; Sutton, Sally J., committee member
The objective of this study was to evaluate the applicability of commercially-available, one-dimensional (1-D) large-strain consolidation programs (FSConsol and CONDES0) for predicting mine tailings consolidation to estimate storage capacity of tailings storage facilities (TSFs). This study consisted of the following tasks: (i) consolidation modeling of well-known benchmark examples from literature, (ii) parametric study to assess the influence of input parameters (i.e., constitutive relationships, initial void ratio, impoundment geometry, and tailings production rate) on consolidation behavior and storage capacity, and (iii) consolidation and storage capacity prediction for a full-scale copper TSF. A benchmark example that represented instantaneous deposition of tailings (Townsend and McVay 1990) was evaluated with CONDES0 and FSConsol and indicated that both models are appropriate for predicting the consolidation behavior of tailings that are deposited instantaneously. Both models yielded similar temporal settlement curves and void ratio profiles. A gradual tailings deposition benchmark example (Gjerapic et al. 2008) was evaluated with both programs and suggested that FSConsol was more applicable for problems dealing with continuous discharge of tailings. In particular, FSConsol was more applicable when the tailings discharge rate varied temporally, which is a key constraint to modeling a full-scale TSF. The parametric study results suggested that the initial tailings void ratio and constitutive relationships (i.e., void ratio versus effective stress, e-σ', and hydraulic conductivity versus void ratio, k-e) had more pronounced effects on consolidation behavior relative to impoundment geometry and tailings production rate. In particular, a comparison between rapidly consolidating mine tailings (copper tailings) and slowly consolidating mine tailings (mature fine tailings from oil sands) indicated that a decrease in hydraulic conductivity by four orders of magnitude can extend the time required for consolidation by more than 200 yr. Changes in impoundment geometry and tailings production rate had limited effects on impoundment capacity for the range of side slopes (1.0H:1V to 4.5H:1V) and production rates (50 mtpd to 300 mtpd) evaluated in this study. FSConsol modeling results from the full-scale copper mine TSF were compared to field data and suggest that a 1-D consolidation model can yield a satisfactory prediction of in-situ consolidation behavior of copper tailings. Comparison between the actual average tailings dry density (ρd) during the first 4 yr of operation and predicted average ρd yielded coefficients of determination (R2) as high as 81 % and 93 % for Operation and Design assessments, respectively. In addition, predicted tailings height within the TSF showed good agreement with actual impoundment heights for the first 6 yr of operation; R2 = 99.1 % for the Operation assessment and cyclone operation time (COT) of 70 %, which was the average actual COT. A procedure was developed to predict average ρd of a full-scale TSF using a 1-D consolidation model that includes the following considerations: (i) estimate total tailings volume in the TSF based on predicted impoundment height and (ii) use this total volume with dry tailings mass discharged into the TSF to compute ρd. The main finding from this study was that the modeling of gradual tailings deposition with FSConsol provides a reliable prediction of impoundment height and impoundment capacity.
Open Access
Phase-based analysis to determine first order decay rates for a bioreactor landfill
(Colorado State University. Libraries, 2017) Nwaokorie, Kelechi J., author; Bareither, Christopher A., advisor; Sharvelle, Sybil E., advisor; von Fischer, Joseph C., committee member
In recent years, the goal of municipal solid waste (MSW) landfill management has transitioned from waste sequestration to waste stabilization. A bioreactor landfill is an MSW landfill operated with a deliberate goal to achieve waste stabilization via in situ organic waste decomposition. Enhanced landfill gas (LFG) generation that results from moisture addition to increase the rate of anaerobic biodegradation can have different consequences on landfill operations. Additionally, landfills commonly are constructed and filled in phases (i.e., delineated areas of the landfill where waste is placed) that are operated with different moisture enhancement strategies. Thus, there is a need to simulate and predict LFG generation in a bioreactor landfill on a phase-specific basis to more accurately assess waste decomposition and progression of organic waste stabilization. In this study, site-wide and phase-specific LFG modeling was conducted for a bioreactor landfill. A phase-specific LFG modeling approach was developed and used to assess six separate phases of the landfill. This approach included a temporal estimate of waste disposal and separation of LFG collection data for the six phases. Landfill gas collection in each phase was used to compute methane collection based on gas composition analyses and used to estimate methane generation based on two considerations of collection efficiency: constant collection efficiency of 85% and temporally varying collection efficiency. Methane generation was predicted using the U.S. EPA LandGEM. Model simulations were compared with adjusted methane collection data to optimize the first-order decay rate (k), which was the primary variable used to assess waste decomposition and stabilization. First-order decay rates were optimized for site-wide and phase-specific analyses that considered (i) monthly versus annual averaging techniques for LFG data, (ii) collection efficiencies, and (iii) LFG collected only in the gas wells versus LFG collected in gas wells and perforated pipes in leachate collection and recirculation systems. The recommended gas modeling approach is to use monthly average LFG flow rates, a constant collection efficiency of 85%, and LFG collected from gas wells and leachate collection / recirculation systems. The optimized k for the site-wide analysis was 0.078 1/yr, whereas the default k for conventional MSW landfills with no moisture enhancement is 0.04 1/yr. Thus, the site-wide k supports enhanced organic waste biodegradation and stabilization. The optimized ks for the phase-specific analyses ranged between 0.025 and 0.13 1/yr, which suggest that although the overall site was operating at an enhanced rate of waste decomposition, the rate varied between landfill phases. Moisture addition via leachate recirculation and liquid waste addition was implemented at the landfill for the five more recent phases. The k values for these five phases increased with increasing liquid addition per waste mass whereby the optimized k values increased from the driest phase, Phase 3 & 4 (0.037 1/yr), to the wettest phase, Phase 6 (0.127 1/yr). The LFG modeling and findings from this study can assist with developing moisture enhancement strategies for bioreactor landfills and assessing LFG collection data to support claims of enhanced waste decomposition and stabilization.
Open Access
Pore fluid salinity effects on sedimentation and geotechnical properties of fine-grained soils
(Colorado State University. Libraries, 2015) H. Gorakhki, Mohammad R., author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Butters, Greg, committee member
The objectives of this study were to evaluate the effects of soluble salt concentration (i.e., salinity) on geotechnical characteristics and sedimentation behavior of fine-grained soils (e.g., mine tailings) and identify test methods applicable for characterizing high-saline soils. Three fine-grained soils were used in this study: soda ash mine tailings, kaolin clay, and bentonite clay. The soda ash mine tailings (sodium carbonate) contained high-saline pore fluid and predominantly sodium on the exchange complex, whereas commercially-available kaolin and bentonite clay were used for comparison with the soda ash tailings. Salinity was controlled in the natural clays via adding salts with different valence (NaCl, CaCl₂, and FeCl₃) at concentrations ranging between 1 and 1000 mM. Salinity in the soda ash tailings was altered via extracting salts from solution using dialysis to create materials with different soluble salt concentrations. Sedimentation experiments were conducted in 63.5-mm-diameter by 457-mm-tall glass cylinders to evaluate the sedimentation rate and final solids content. The effects of pore fluid salinity on geotechnical characteristics of soda ash mine tailings and laboratory-prepared, sedimented soils were evaluated via measuring Atterberg limits, specific gravity, and particle-size distribution via hydrometer tests. Overall, an increase in ionic strength of the sedimentation fluid (i.e., increase in salt concentration) yielded higher sedimentation rates and larger volumes of released water for experiments on bentonite. In contrast, the sedimentation rate of kaolin was constant for salt concentrations between 1 and 100 mM, and the sedimentation rate decreased at higher salt concentrations. This behavior was attributed to an increase in fluid density and viscosity at high salt concentrations that reduced sedimentation. Soda ash sedimentation behavior was similar to kaolin and characterized by a decrease in sedimentation rate with increase in salt concentration. Geotechnical characterization of all materials indicated that liquid limit, plastic limit, and clay content decreased with increasing pore fluid salinity. Temporal evaluations of soil plasticity suggest that hydration times of at least two days are required to solubilize salts and capture salinity effects on soil plasticity. Additionally, experimental methods were developed and evaluated for correcting errors in hydrometer and specific gravity tests that may originate in the presence of soluble salts.
Open Access
Predicting water content and saturation in mine tailings with an electromagnetic soil moisture sensor
(Colorado State University. Libraries, 2023) Martin, Garret M., author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Ham, Jay M., committee member
The degree of saturation of mine tailings plays an important role in geotechnical and geochemical stability of a tailings facility, and as such, reliable measurements of in situ tailings saturation aid in evaluating the stability of a tailings facility. However, measuring in situ saturation in tailings facilities is a common challenge in the tailings industry. The objectives of this study were to (1) evaluate the ability of an electromagnetic soil moisture sensor to predict the volumetric water content and degree of saturation of mine tailings and (2) conduct proof-of-concept tests to assess the potential for electromagnetic sensors to be used as a tool in tailings engineering practice. To meet these objectives, laboratory-scale testing was conducted using an electromagnetic soil moisture sensor embedded in moist-tamped and slurry-deposited specimens of a single hardrock mine tailings prepared at varying volumetric water content, degree of saturation, and dry density. Certain specimens were subjected to changes in mass-volume properties and sensor performance was evaluated for timeliness and accuracy of response. The results of this study indicate an electromagnetic soil moisture sensor can be used to predict the volumetric water content and degree of saturation in hardrock mine tailings with a useful degree of accuracy depending on the application and precision required. During the proof of concept tests performed, error in predicted volumetric water content was less than about 1.5% to 3.8%, error in predicted saturation was predominantly less than 5%, and temporal response to changes in moisture was equivalent to a sensor insertion rate of approximately 27 mm/s. Based on the findings of this study, electromagnetic sensor technology offers a viable tool to predict the degree of saturation within tailings facilities and can be incorporated into innovative approaches to address the challenges encountered in different types of tailings facilities.
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 member
The 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.
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.
Open Access
Shear behavior of geosynthetic clay liners and textured geomembranes in mining applications
(Colorado State University. Libraries, 2019) Ghazi Zadeh, Shahin, author; Bareither, Christopher A., advisor; Shackelford, Charles D., committee member; Scalia, Joseph, committee member; Bailey, Travis, committee member
The objective of this study was to evaluate the shear behavior of a composite system consisting of geosynthetic clay liner (GCL) and textured geomembrane (GMX) in mining applications. In current practice, design of liner and cover systems for waste containment is based on results of displacement-controlled internal and interface shear tests, which commonly include GCL and GMX specimens hydrated in de-ionized or tap water and tested at room temperature (e.g., 20 °C). However, the use of GCL/GMX composite systems in liner and/or cover systems for mine waste containment (e.g., heap leach pads, tailings impoundments, waste rock piles) may be exposed to physical and environmental stresses that are not conventionally replicated in laboratory testing, such as high shear and normal stresses, elevated temperature, and/or non-standard solutions. Laboratory testing conducted under conventional experimental conditions may not represent appropriate stresses anticipated in field conditions. To address the aforementioned concerns and aid the design of liner and cover systems for mining applications, four main objectives were defined: (i) assess variability of internal reinforcement fibers and shear strength in GCLs; (ii) evaluate the effect of GCL and GMX characteristics on shear behavior of GCL/GMX composite systems; (iii) evaluate temperature effects on the shear behavior of GCL/GMX composite systems; and (iv) evaluation the effects of non-standard solutions on GCL internal and GCL/GMX interface shear strength. These objectives were addressed via laboratory experiments, which included approximately 400 direct shear tests, 150 peel strength tests, and 50 swell index tests. Comparable internal shear behavior was observed between 300 mm x 300 mm GCL specimens and 150 mm x 150 mm GCL specimens. Similar variability in peak internal shear strength was also observed in both size GCL specimens. Variation was also observed in GCL peel strength among specimens obtained from the same production roll. Variability in internal shear strength and peel strength were attributed to the spatial variability of reinforcement fiber characteristics within a given GCL roll. The failure mode of a GCL/GMX composite system in an interface direct shear test was a function of shearing normal stress and characteristics of the GCLs and GMXs. An increase in spike density of a GMX increased the critical strength of GCL/GMX composites at all normal stress. However, an increase in GCL peel strength most effectively increased critical strength of a GCL/GMX composite at high normal stresses when GCL internal failure occurred. Internal and interface direct shear testing at an elevated temperature to 80 °C resulted in reductions of both GCL internal and GCL/GMX interface shear strength. The reduction in GCL internal shear strength was due to a reduction in tensile strength of reinforcement fibers and reduction in the strength of the connection between reinforcement fibers and geotextile of the GCL. The reduction in GCL/GMX interface shear strength was attributed to a reduction in the interlocking strength between GMX spikes and fibers of the geotextile of the GCL, as well as a reduction in geotextile-GMX interface friction. Hydration of GCL and GMX specimens up to 10 months in synthetic acidic and alkaline mining process solutions did not produce noteworthy change in GCL internal shear strength, GCL-GMX interface shear strength, or GCL peel strength. However, stiffer shear behavior was observed in internal and interface shear tests on GCL and GMX specimens hydrated with the synthetic acidic mine process solution. Hydration with the synthetic acidic mine process solution reduced swell behavior of sodium bentonite, whereas no conclusions were made regarding the effect of hydration with alkaline mine process solution on bentonite swell behavior.
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 member
The 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.