Browsing by Author "Shackelford, Charles D., committee member"
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Item 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 memberThe 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.Item 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 memberAn 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.Item Open Access Beneficial use of off-specification fly ashes to increase the shear strength and stiffness of expansive soil-rubber (ESR) mixtures(Colorado State University. Libraries, 2011) Wiechert, Ethan Patrick, author; Carraro, J. Antonio H., advisor; Guggemos, Angela A., committee member; Shackelford, Charles D., committee memberThe potential use of off-specification fly ashes to increase the shear strength and stiffness of an expansive soil-rubber (ESR) mixture was investigated systematically in this study. The off-specification fly ashes used included a high sulfur content fly ash and a high carbon content fly ash. A standard Class C fly ash was also used as a control fly ash to develop a basis for comparison of the effects of the off-specification fly ashes. The ESR mixture consisted of high-plasticity clay blended with 20% 6.7-mm granulated rubber (by weight). The fly ash content required to develop pozzolanic reactions was determined based on the concept of lime fixation point and kept constant for all ESR-fly ash mixtures. At this selected fly ash content, ESR-fly ash mixtures were tested at a single relative compaction level and curing times of 7 and 14 days. Unconfined compression testing was performed on compacted specimens to validate the fly ash content selected and the effect of curing time on the development of pozzolanic reactions. The effect of the fly ash type, curing time and mean effective stress was evaluated by performing isotropically consolidated undrained triaxial compression tests on saturated specimens at mean effective stress levels of 50, 100 and 200 kPa. Stiffness changes due to fly ash addition were evaluated during undrained compression. Large-strain stiffness was measured using conventional external displacement transducers. Very-small strain stiffness was evaluated from shear wave velocity measurements using a bender element apparatus. Results suggest that the shear strength and stiffness improvements imparted by the off-specification fly ashes is similar to or better than the improvements imparted by conventional Class C fly ash.Item Open Access Critical state, dilatancy and particle breakage of mine waste rock(Colorado State University. Libraries, 2011) Fox, Zachary P., author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Borch, Thomas, committee member; Overton, Daniel D., committee memberCritical state, dilatancy and particle breakage characteristics of two mine waste rock (MWR) materials were systematically studied in drained isotropic and axisymmetric compression. A specimen preparation technique that simulated material dumping in the field was adopted and the technique is shown to be suitable for reconstitution of uniform and repeatable specimens of MWR for element testing. The MWR types tested were unoxidized and oxidized sedimentary argillite taken from the Ordovician Vinini formation in northeastern Nevada. Acid-base accounting results indicate that the neutralization potential (NP) and acid-producing potential (AP) values decreased for the oxidized material. Static, monotonic, isotropically compressed drained triaxial tests were performed on 150-mm-diameter, 300-mm-tall cylindrical specimens with maximum particle size equal to 25.4 mm. Laboratory particle size distributions were modeled to be parallel to the collected field gradation in order to create specimens with appropriate maximum particle sizes for the testing apparatus. The intrinsic parameters that characterize critical-state, dilatancy and particle breakage of each MWR material tested were determined allowing analysis of constitutive behavior to be carried out using an appropriate theoretical framework for granular soils experiencing particle breakage during testing. While the critical state friction angles were very similar between the two MWR types (unoxidized = 38.3° and oxidized = 36.7°), dilatancy is much greater in the unoxidized specimens than in the oxidized specimens. Bolton's (1986) fitting parameters Q and R were determined and values agree well with those found in the literature for geomaterials with similar stress-dilatancy behavior and grain tensile strengths. Grain tensile strength was evaluated through point load strength index testing giving values for grain tensile strength for the unoxidized material that are 10 times greater than observed for the oxidized material. Particle size distributions were determined before and after testing to evaluate particle breakage due to the combined effects of isotropic and axisymmetric compression as well as evaluate the increase in surface area due to particle breakage. The fractal dimension (D) was evaluated before and after testing in order to assess the validity of the underlying assumptions of the modified work equation presented by McDowell et al. (1996). The surface energy of the materials tested was found to be in the range of 5-24 J/m2. All of these results indicate that in situ weathering may degrade the shear strength characteristics of a quarried sedimentary mine waste rockfill by weakening the intrinsic shear strength parameters of the MWR. The only rigorous way to properly assess the strength degradation of the MWR materials tested involves careful assessment of the critical state, dilatancy and particle breakage characteristics.Item 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 memberThe 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.Item Open Access Effects of maximum particle size and sample scaling on the mechanical behavior of mine waste rock; a critical state approach(Colorado State University. Libraries, 2012) Stoeber, Justin Neil, author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Schutt, Derek L., committee memberA rigorous and systematic study on the effects of maximum particle size and sample scaling on the mechanical behavior of mine waste rock (MWR) is presented. Materials tested were obtained from a similar location within the open pit of Barrick Gold Corporation's Goldstrike gold mine approximately 60 km northwest of Elko, Nevada. The collected field gradation was scaled using the parallel gradation technique in order to most accurately reproduce the fabric of the collected field material in the laboratory. The two MWR materials were shown to have drastically different mineralogy, which may be due to varying levels of in situ hydrogeologic weathering. Mechanical behavior of two MWR materials was systematically evaluated on 70-mm-diameter, 140-mm-tall specimens with a maximum particle size equal to 11.2 mm in drained isotropic and monotonic axisymmetric compression using a conventional triaxial device. Results from conventional triaxial tests in drained isotropic and monotonic axisymmetric compression were systematically compared to results presented by Fox (2011) for 150-mm-diamer, 300-mm-tall specimens with a maximum particle size equal to 25.0 mm for the same MWR materials also scaled using the parallel gradation technique and tested at the same levels of mean effective stress (p') in a large-scale triaxial device. Intrinsic critical state parameters were defined for each material in conventional scale triaxial testing. Results suggest the parallel gradation technique provides a reasonable way to estimate values of intrinsic critical state parameters during isotropic compression in large-scale applications using conventional triaxial tests provided that the range of DR,Initial is similar between scales. Values of the critical state friction angle (ϕc) were determined to be within 2° of the larger scale specimens. Dilatancy rates measured in conventional scale unweathered specimens was found to be, on average, approximately twice of that measured in the large-scale specimens of the same material. The weathered material indicated no significant changes in average dilatancy rates between scales. Bolton's (1986) fitting parameters Q and R were determined to decrease with decreasing particle size where Bolton's stress - dilatancy relationship was found to predict values of the peak friction angle (ϕp) more accurately using values of Q and R obtained in large-scale triaxial tests where conventional scale specimens yielded consistently unconservative predictions of ϕp suggesting that conventional triaxial tests should not solely be used to characterize the mechanical behavior of large-scale materials. Particle breakage measured after each triaxial test indicated a relatively constant shift from pre to post-test particle-size distribution curves between conventional and large-scale specimens. Additional results and comparisons of values such as fractal dimension (D) and surface energy (Γse) are also discussed.Item Open Access Fatigue and rutting analyses of a pavement structure with expansive soil-rubber (ESR) base stabilized with off-specification fly ash(Colorado State University. Libraries, 2012) Budagher, Emily L., author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Funk, Loren G., committee memberThe focus of this study is to analyze through resilient modulus testing and computer simulations the feasibility of an expansive soil-rubber (ESR) mixture stabilized with off-specification fly ash (ESR-FA) as a pavement base layer. Three mixtures were tested in this study, which were expansive soil, ESR, and ESR-FA mixtures. The off-specification fly ash used included a high sulfur content. The ESR mixture consisted of high-plasticity clay blended with 20% 6.7-mm granulated rubber (by weight). The ESR-FA consisted of the same high-plasticity clay blended with 20% 6.7-mm granulated rubber (by weight) and 14% fly ash. All mixtures were tested at a target relative compaction level equal to 95% (±0.5%) of the Standard Proctor maximum dry density. Expansive soil and ESR specimens were subjected to resilient modulus and Poisson's ratio testing immediately after compaction. ESR-FA specimens were allowed to cure for 14 days before being subjected to resilient modulus and Poisson's ratio testing. All specimens were unsaturated during testing. Stiffness changes due to scrap tire rubber addition and fly ash addition were evaluated during resilient modulus testing. Poisson's ratio was determined using axial and radial transducers during unconfined compression testing. Results suggest that the stiffness of the expansive soil specimen is significantly greater than that of the ESR and ESR-FA specimens. However, the stiffness of the ESR-FA specimen is greater than that of the ESR specimen, which makes it a medium between the expansive soil specimen and the ESR specimen.Item Open Access Feasibility of treating chlorinated solvents stored in low permeability zones in sandy aquifers(Colorado State University. Libraries, 2012) Bolhari, Azadeh, author; Sale, Thomas C., advisor; Bau, Domenico A., committee member; Shackelford, Charles D., committee member; Borch, Thomas, committee memberTo view the abstract, please see the full text of the document.Item Open Access Graywater application for landscape irrigation: greenhouse studies(Colorado State University. Libraries, 2010) Shogbon, Alicia R., author; Sharvelle, Sybil E., advisor; Shackelford, Charles D., committee member; Qian, Yaling, committee memberOver the years, residential graywater application for landscape irrigation has garnered increasing popularity. Concerns however exist regarding the potential negative impacts that graywater pose to plant health and environmental quality. Due to the variability in field conditions such as graywater loading rate, soil type, climate and rainfall amount difficulty exists in accurately determining the potential for groundwater contamination. The need therefore arises to evaluate impacts of graywater irrigation in a controlled environment to develop scientifically justified conclusions regarding the fate of graywater constituents. The objective of this study was to conduct experiments in a greenhouse to evaluate the potential for groundwater contamination by conducting leachate analysis. Plant health was also evaluated throughout the duration of the experiment. The experiment setup involved the use of thirty-eight custom polyvinyl chloride (PVC) pots. These pots were setup in the Colorado State University greenhouse. Potable water served as a control for the experiments. Two different plants and two different turfgrasses were utilized. The turfgrasses were bermudagrass (a warm season grass) and tall fescue (a cool season grass). The landscape plants used were euonymous (a shrub) and lemon (a citrus). The pots were setup to allow for leachate collection from the bottom. The leachate volume was monitored and recorded and leachate analyses were conducted for boron, sodium adsorption ratio (SAR), nitrate, ammonium, total nitrogen (TN), total dissolved solids (TDS), total suspended solids (TSS), volatile suspended solids (VSS), total organic carbon (TOC), sulfate, conductivity and surfactants (linear alkylbenzene sulfonate (LAS), alkyl ethoxy sulfate (AES), and alcohol ethoxylate (AE)). Analysis of the leachate from the graywater irrigated pots revealed on average, elevated levels of TOC, TN, nitrate, ammonium, TDS, TSS, VSS, sulfate, conductivity, boron and SAR when compared to the concentrations measured in the leachate from the control systems. The average concentrations of TOC, TSS, VSS , ammonium, nitrate and TN measured in the leachate from the graywater irrigated plant/grass systems were however lower than the concentrations in the synthetic graywater. An expected increase in conductivity and TDS in the leachate from the graywater irrigated pots was found. Results further indicate the accumulation of boron and salts (indicated by SAR) in the graywater systems with a trend of increasing concentrations with time and a subsequent increase in measured leachate concentrations above the input concentration measured in the graywater. With the exception of boron and salts, there was substantial percentage retention of graywater constituents through the soil column such that there was lower measured concentrations of the graywater constituents in the soil leachate compared to the input concentrations.Item 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 memberThe 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.Item 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 memberThe 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.Item Open Access Resolving natural losses of LNAPL using CO2 traps(Colorado State University. Libraries, 2012) McCoy, Kevin M., author; Sale, Thomas C., advisor; Zimbron, Julio A., advisor; Shackelford, Charles D., committee member; Ronayne, Michael, committee memberPools of light non-aqueous phase liquids (LNAPLs) are a legacy of past practices at petroleum facilities. Traditional LNAPL remedies (e.g. hydraulic LNAPL recovery) are often costly and have limited effectiveness. Recent studies have indicated that natural losses of LNAPL can help to stabilize and even shrink subsurface LNAPL bodies once the LNAPL source is removed. Developing an effective understanding of natural losses of LNAPL is an important step in establishing LNAPL management strategies. Estimated rates of natural losses of LNAPL can be used to demonstrate LNAPL stability, form a basis for initiating or discontinuing hydraulic recovery, estimate longevity of LNAPL bodies, and as a benchmark to compare relative effectiveness of different remedial alternatives. Additionally, an understanding of underlying processes gained through field studies can guide development of new, more sustainable LNAPL remediation technologies. A novel integral CO2 Trap was created to measure soil CO2 efflux at grade. This addresses a need for an efficient tool to quantify natural losses of LNAPL. The hypothesis of this thesis is that CO2 Traps can be used to quantify natural losses of LNAPL at field sites. Laboratory and field tests were performed to test the CO2 Traps and demonstrate their utility. First, laboratory experiments were undertaken to demonstrate the ability of the traps to quantitatively capture CO2 and effectively estimate CO2 fluxes. Closed system column testing showed that the selected sorbent media is capable of quantitatively recovering CO2. This testing also verified that the sorption capacity of the media (~30% CO2 by mass) was in the range indicated by the manufacturer. This information is useful when planning maximum field deployment times, and as a means of quality checking field sampling results. Next, an open system column test showed that the CO2 Traps are capable of quantitatively measuring CO2 flux through porous media. The traps were field tested. Results of a single round of CO2 Trap deployment at one field site showed that the traps could distinguish zones of elevated CO2 flux over the LNAPL body, relative to naturally occurring CO2 flux at background locations. Background subtracted LNAPL loss rates ranging from 800 to 12,000 gallons per acre per year (gal/acre/yr) were observed. Carbon isotope analysis was performed on one travel blank sample, two background samples, and one LNAPL area sample. Radiocarbon (14C) results provided an independent means to estimate naturally occurring CO2 flux. Results of the 14C correction agreed well with the background subtraction method for that location. CO2 traps have been deployed at a total of 117 locations at 6 field sties. Seasonal resampling of selected locations has yielded a total of 194 CO2 flux readings. Calculated background corrected LNAPL loss rates for ranged from 400 - 18,000 gal/acre/yr with a mean of 3,500 gal/acre/yr. A detailed analysis of the influence of site and LNAPL characteristics on calculated LNAPL loss rates was performed for one of the six sites. Results indicated that natural losses of LNAPL are largely independent of in-well LNAPL thickness, depth to smear zone, smear zone thickness, or LNAPL type. However, temperature related seasonal trends were observed. Furthermore, natural losses of LNAPL appear to result in self heating of LNAPL zones with a potential benefit of enhancing natural losses. Additional data analysis suggests a link between temperature and natural LNAPL loss rate that may be useful in developing new, more sustainable, LNAPL management technologies.Item Open Access Retardation and reaction in low permeability layers in groundwater plumes(Colorado State University. Libraries, 2013) Wahlberg, Jennifer J., author; Sale, Thomas C., advisor; Shackelford, Charles D., committee member; Dandy, David S., committee memberTo view the abstract, please see the full text of the document.Item 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 memberThe 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.Item Open Access Shear strength and stiffness of a Sahara sand from Libya(Colorado State University. Libraries, 2011) Badanagki, Mahir, author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Shuler, Scott, committee memberModern geotechnical analyses rely upon a rigorous characterization of the dilatancy, critical state and stiffness parameters of geomaterials. In order to generate a fundamental database for these parameters for future geotechnical projects in Libya, the shear strength and stiffness of Libyan Sahara sand were systematically studied in drained and undrained axisymmetric compression. The dry funnel deposition method was employed in this study to create homogenous specimens and simulate the natural fabric of aeolian sand deposits from Libya. The fabric of Sahara sand was examined using a Scanning Electron Microscope (SEM). Static, monotonic, isotropically-compressed drained and undrained triaxial tests were performed on specimens with nominal height and diameter equal to 140 and 70 mm, respectively, to characterize the stress-strain-volumetric (or stress-strain-excess pore pressure) response and determine the intrinsic parameters of Libyan Sahara sand. Bender element tests were also performed to measure the shear wave velocity (Vs) and estimate the small strain shear modulus (Gmax) of Sahara sand at mean effective stress levels of 50, 100, 200 and 400 kPa. The intrinsic parameters that characterize isotropic compression, critical-state, dilatancy and small-strain stiffness of Libyan Sahara sand were determined to allow future analyses of mechanical behavior for this soil to be carried out using a rigorous theoretical framework for granular soils. The critical state soil parameters Γ, λ and k of the Libyan Sahara sand were determined to be equal to 1.92, 0.031 and 0.0002, respectively. The critical state friction angle (φc) of the soil was found to be equal to 31.9° based on results from both drained and undrained tests. The value of φc determined from drained tests was found to be in perfect agreement with the value of φc determined from undrained tests, as expected. The intrinsic parameters Q and R of the peak friction angle (φp) correlation (Bolton 1986) were determined to be equal to 8.5 and 0.98, respectively. This allowed prediction of φp values that differed by no more than about 1° from the actual values measured during the triaxial tests performed under a wide range of relative densities and mean effective stresses. The very small strain stiffness parameters Cg, ng and eg of the Libyan Sahara sand were equal to 548, 0.51 and 2.17, respectively. While the Libyan Sahara sand tested has about 25% of nonplastic fines, results from this fundamental study suggest that the isotropic compression, critical-state, dilatancy and small-strain stiffness characteristics of this soil can be reasonably interpreted according to (or predicted by) a rigorous framework that has already been validated for clean sands and/or sands containing fines.Item Open Access Structural evolution of the gold quarry deposit and implications for development, Eureka County, Nevada(Colorado State University. Libraries, 1995) Cole, David M., author; Thompson, Tommy B., advisor; Shackelford, Charles D., committee member; Erslev, Eric A., committee memberThe Gold Quarry deposit, located seven miles north of Carlin, Nevada, is a bulk-minable sediment-hosted disseminated gold deposit situated along the Carlin Trend in Eureka County. A premier gold deposit in North America, Gold Quarry has total in-place reserves, and past production which exceed 15,000,000 oz. gold. Gold Quarry is hosted by lower Paleozoic eastern assemblage carbonate rocks, and lower Paleozoic siliciclastic and siliceous rocks of the transitional and western assemblage facies. The deposit is localized by a major structural intersection of the Gold Quarry and Good Hope fault systems at the southern end of the Carlin window. The Carlin window comprises an exposure of lower-plate eastern assemblage carbonate rocks through the upper-plate western assemblage siliceous rocks and the Tertiary Carlin Formation. The window is bounded by the Gold Quarry fault to the southeast and the Good Hope fault to the southwest. The Gold Quarry deposit comprises four connected mineral zones, and several other small satellite deposits within one large mineral system. The four zones are Gold Quarry Main, Maggie Creek, Deep West, and Deep Sulfide Feeder. These are believed to be genetically related, but differ from one another due to local stratigraphic and structural ore-controls. Detailed pit mapping and drill-log interpretation, aided by palynologic dating techniques integrated with research conducted by other workers has yielded a coherent tectono-stratigraphic sequence for the Gold Quarry area. Eastern-assemblage carbonate rocks, including the Ordovician Hanson Creek, Silurian Roberts Mountains Formation and a sequence of Devonian unnamed limestones, are in fault contact with upper Devonian siliciclastic rocks in the hanging wall of the Gold Quarry/Chukar Gulch fault. Locally termed the Quarry Member, this siliciclastic sequence includes laminated siltstone and lesser rhythmically bedded cherty-mudstone and siltstone. The bulk of the siliciclastic sequence has been dated as Frasnian to Famennian (uppermost Devonian); however, the upper portions of the unit have yielded Kinderhookian (lowest Mississippian) dates. Highly folded and thrusted limestone of Devonian and Silurian ages are found in thrust contact above the siliciclastic sequence. This folded and thrusted package is locally referred to as the "allochthonous limestone wedge". The next tectono-stratigraphic higher package of rocks is the upper-plate to a major thrust fault locally referred to as the "Roberts Mountains Thrust"(RMT). The locally termed RMT is only one thrust plane within a sequence of thrusts, which comprise the regionally recognized RMT zone. These upper-plate Caradocian (middle Ordovician) rocks include rhythmically bedded cherty mudstone and shale, laminated siltstone and lesser quartzite interbeds. A structural model for Gold Quarry has been developed based on an integration of detailed mapping, structural and ore-control data from the Maggie Creek sub district. A structural para-genesis, based on crosscutting relations of mapped faults and fault lineation, is proposed. Evidence for four main stages of faulting is noted at Gold Quarry: 1) Compression-driven thrusting and related folding; 2) Wrench-driven strike-slip, reverse and dilatational faulting; 3) Formation of collapse due to decarbonatization of host-rocks and associated normal faulting; and 4) Extensional tectonics resulting in normal faulting. The oldest faulting and folding events at Gold Quarry are low-angle; generally, east-dipping thrust faults and associated folds developed within the Devonian siliciclastic rocks and the overlying Ordovician siliceous rocks. The next sequence of faulting is wrench-related, driven by a north-northeast principal compressive stress. This episode is interpreted to be responsible for forming the Carlin window, developing in response to a reverse-fault accommodation of movement along the Gold Quarry left-lateral shear. The Gold Quarry deposit is located at the "cornerstone" or structural intersection of the Gold Hope reverse-fault and the Gold Quarry left lateral shear. In addition, dominant ore-control directions are controlled by N 10° W to N 200° W (350° to 340°) right-lateral faults of lesser magnitude positioned in a conjugate manner to the Gold Quarry fault system. An important structural event of the Gold Quarry main zone is volume-loss collapse of the system host rocks caused by extensive decarbonatization during hydrothermal alteration. Bakken (1990) documented 50% volume loss of the ore-host silty carbonate rocks at the Carlin deposit. A similar amount of volume-loss would be expected for decalcified and dedolomitized silty carbonate rocks in the footwall of the Gold Quarry Main zone. Volume-loss accommodation driven collapse and associated normal faulting, in addition to preexisting fracturing, rendered the otherwise poor host rocks of the siliciclastic sequence amenable to fracture-controlled ore-fluid penetration. Significant extension-driven normal faulting and associated rotation of the deposit region occurred during the development of the Basin and Range. The extension reactivated many pre-existing structures as normal faults, most notably, the northeast trending faults such as the Gold Quarry fault system. Dip-slip slickensides are common cross-cutting the low angle mullions and grooves on many of the northeast and north-northwest-trending faults. The post-ore Tertiary Carlin Formation is offset, as well, by normal faults.Item Open Access Swell, stiffness and strength of expansive soil-rubber (ESR) mixtures at various scales: effect of specimen and rubber particle sizes(Colorado State University. Libraries, 2012) Heyer, Lance C., author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Butters, Gregory, committee memberExpansive soils and stockpiled scrap tires present unique constructability and environmental challenges to the Front Range of Northern Colorado, respectively. Swell, stiffness and strength parameters of expansive soil-rubber (ESR) mixtures were systematically evaluated in the laboratory under one-dimensional and axisymmetric boundary conditions. ESR mixtures tested contained highly plastic, swelling clay from the Pierre shale formation and scrap tire rubber (STR) with nominal maximum particle sizes equal to approximately 6.7 or 19.0 mm. Compaction parameters were determined using standard Proctor compaction procedures (ASTM D698). Mixtures were compacted to relative compaction levels equal to 90, 95 or 100% and water contents varying by ± 2% around the optimum water content. Rubber contents used were equal to 0, 10 or 20%. Specimen and rubber particle sizes were also studied to assess differences in mechanical behavior of 6.7- and 19.0-mm ESR mixtures tested in one-dimensional compression employing three specimen sizes (small-scale, large-scale and field-scale) and in undrained axisymmetric compression employing two specimen sizes (small-scale and large-scale). Swell-compression results indicated the swell percent and swell pressure of specimens subjected to one-dimensional compression with lateral confinement were most impacted by initial water content, followed by relative compaction and rubber content. Compressibility parameters, including the constrained and elastic moduli, are most impacted by rubber content, followed by relative compaction and initial water content. Small-scale one-dimensional specimens demonstrated a minimal increase in swelling and insignificant variations in compressibility in comparison to large-scale one-dimensional and field-scale specimens. ESR specimens subjected to axisymmetric boundary conditions exhibited volumetric swell during flushing and back pressure saturation and swelling magnitudes were similar for nominal rubber particle sizes equal to 6.7 and 19.0 mm. Normal compression line parameters, λcs and κcs, were equal to 0.10 and 0.05, and 0.11 and 0.04 for large-scale 6.7- and 19.0-mm ESR specimens, respectively. Critical state parameters, Mcs, Γcs, and λcs, were equal to 1.20, 2.23 and 0.14, and 1.04, 2.15 and 0.13 for large-scale 6.7- and 19.0-mm ESR specimens, respectively. Scalability results indicate similar swell, stiffness and strength of ESR mixtures compacted to various specimen sizes with the inclusion of either 6.7- or 19.0-mm scrap tire rubber particles. Results indicate reasonable predictions of the mechanical behavior of ESR mixtures including tire chips can be made using conventional laboratory specimen sizes and testing techniques employing similar host expansive soils and rubber contents used to create ESR mixtures including granulated rubber.Item Open Access Unsaturated fluid flow and volume change behavior of filtered tailings(Colorado State University. Libraries, 2022) Aghazamani, Neelufar, author; Scalia, Joseph, IV, advisor; Bareither, Christopher A., committee member; Shackelford, Charles D., committee member; Ham, Jay M., committee memberAs the global demand for minerals continues to increase so does the generation of mine waste. Tremendous volumes of mine waste, viz. tailings and waste rock, are generated and placed in impoundments and piles. Improved methodologies are needed to enhance the sustainability of mine waste management. Tailings are typically discharged as a slurry of finely ground rock within water to a settling facility contained by an embankment. These facilities often necessitate long-term management of inherently weak materials. Tailings dewatered via filtration yields enhanced water stewardship and greater geotechnical stability; filtered tailings are readily amenable to progressive closure and environmental restoration. But, the high cost of tailings filtration, and the potential for acid rock drainage (ARD) due to oxygen ingress and internal unsaturated flow of water have limited the adoption of filtered tailings by the mining industry. The goal of this study is to advance the state of knowledge of filtered tailings. To this end, this dissertation consists of three components; (1) assessing the influence of filtered tailings placement conditions on filtered tailings unsaturated characteristics, (2) assessing excess pore pressure generation during compression of unsaturated filtered tailings, and (3) exploring hydrologic paths to minimize ARD and improve geochemical stability of filtered tailings stacks. Pressure plate, chilled mirror, and shrinkage curve tests were performed to produce soil water characteristic curves (SWCCs) for two precious metal mine tailings with varying initial water contents and dry densities. The resultant SWCCs illustrate that the placement water content and dry density have a significant influence on the unsaturated characteristics of the filtered tailings. Generation of excess pore water pressure was assessed via undrained compression tests. Unsaturated filtered tailings started generating appreciable excess porewater pressure (> 10% of the incrementally applied total vertical stress) when the saturation of the tailings was at the range of 80 to 90%; this appreciable excess pore pressure did not fully dissipate after 24 h. Filtered tailings in this study followed a stress path with void ratios below the critical state line (i.e., dilative during undrained shear) unless placed initially loose and wet. The SWCCs produced were used to model the hydrology of filtered tailings and comingled filtered tailings columns via HYDRUS-2D in example wet, hemiboreal, and dry climates. Results of this study illustrate that for the filtered tailings evaluated in this study, ARD is anticipated to be minimized via varying climate-dependent mechanisms. In the arid climate, filtered tailings functioned as a water balance layer, storing, and releasing precipitation as evaporation not percolation. In the wet climate, filtered tailings became rapidly saturated and maintained a saturated surficial layer preventing inward movement of oxygen and potentially minimizing generation of ARD. In the hemiboreal and wet climates percolation was minimal due to the low hydraulic conductivity of the filtered tailings, and inclusion of a commingled capillary barrier layer further reduced percolation (further reducing the potential flux of ARD). Results from this study illustrate the potential efficacy of filtered tailings to maintain both geotechnical stability and limit ARD.