Browsing by Subject "Soil"
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Item Analytical, experimental, and field evaluations of soil-geosynthetic interaction under small displacements(2016-08) Roodi, Gholam Hossein; Zornberg, Jorge G.; Stokoe, Kenneth H; Gilbert, Robert B; Prozzi, Jorge A; Taleff, Eric MThe increasing use of geosynthetics in stabilization of pavement systems under traffic loads and environmental changes requires proper understanding of the mechanisms that govern the soil-geosynthetic interaction. Significant research has already been conducted on the soil-geosynthetic interaction under ultimate conditions, which is relevant to reinforcement of retaining walls and steep slopes. However, little research has been undertaken to investigate the properties and mechanisms that govern the soil-geosynthetic interaction under small displacements, which is relevant to applications such as the geosynthetic stabilization of pavement layers. While characterization of the maximum geosynthetic strength (e.g., tensile strength or pullout resistance) is relevant for the design of soil-geosynthetic systems under ultimate conditions, proper design properties in systems where geosynthetics are used to control deformations should involve characterization of the stiffness of soil-geosynthetic composite. The objective of this research is to develop a better understanding of the soil-geosynthetic interaction under small displacements using analytical, experimental, and field evaluations. Three studies were conducted on different aspects of soil-geosynthetic interaction under small displacements: (1) Analytical and experimental evaluations of the soil-geosynthetic composite (SGC) model using large-scale soil-geosynthetic interaction tests, (2) analytical and experimental evaluations of soil-geosynthetic interaction using small-scale soil-geosynthetic interaction tests, and (3) field evaluation of soil-geosynthetic interaction under small displacements. Each study provides lessons and conclusions on specific aspects investigated in that study. Collectively, they suggest that the analytical model proposed in this study provides a good basis towards predicting the general performance of geosynthetic-stabilized pavements. The analytical formulation of the SGC model indicates that soil-geosynthetic interaction under small displacements can be characterized by the stiffness of soil-geosynthetic composite ( ), which is the slope of the linear relationship defined between the unit tension squared (T2) versus displacements (u) in each point along the active length of a geosynthetic. The linearity and uniqueness of the relationship between the unit tension squared (T2) and displacements (u) throughout the active length of specimens tested in a comparatively large soil-geosynthetic interaction device were experimentally confirmed. Overall, the experimental results from the large-scale soil-geosynthetic interaction tests were found to be in good agreement with the adopted constitutive relationships and with the analytical predictions of the SGC model. Evaluation of experimental results from tests conducted to assess repeatability indicated that the variability of the estimated values for the constitutive parameters ( and ) and the stiffness of soil-geosynthetic composite ( ) are well within the acceptable ranges when compared to variations of other soil and geosynthetic properties. Suitability of the assumptions and outcomes of the model was also confirmed for a variety of testing conditions and materials. Evaluation of the experimental data obtained from a subsequent experimental program involving small-scale soil-geosynthetic interaction tests indicates that although the assumptions of the analytical model do not fully conform to the conditions in a small-scale test, experimental results confirm the linearity and uniqueness of the relationship between the unit tension squared (T2) and the displacements (u) throughout the specimen. Evaluation of the results obtained from small- and large-scale interaction tests on five geosynthetics with a range of properties indicates that both large and small testing scales can be used for comparative evaluation of the stiffness of soil-geosynthetic composite among geosynthetics. However, since the stiffness values obtained from the two testing scales were found to be different, the stiffness values from the large-scale soil-geosynthetic interaction tests should be suitable for design purposes, while values from the small-scale interaction tests should be suitable for specification and comparison purposes. Evaluation of the long-term performance of full-scale paved test sections under both traffic and environmental loads indicates that stabilization with geosynthetics contributes to improving the road performance under both loading conditions. The benefits derived from using geosynthetics under traffic loads were realized by reducing the total length of rut or rutting depth. On the other hands, the benefits from using geosynthetics under environmental loads in roads founded on expansive subgrades were realized by mitigating the percentage of longitudinal cracks appears on the road surface. The latter benefits were found to be more pronounced towards the end of dry seasons, when longitudinal cracks tend to develop. Comparison among the performances of geosynthetic-stabilized test sections under environmental loads indicate that the benefit provided by geosynthetics correlates well with the stiffness of soil-geosynthetic composite ( ) characterized in the laboratory. Geosynthetic products with comparatively larger were found to lead to a comparatively better field performance.Item Bioaccumulation and effects of metal contaminated soil on Great Plains toads, Bufo cognatus.(Texas Tech University, 2008-08) Bryer, Pamela Jean; McMurry, Scott T.; Cox, Stephen B.; Hooper, Michael J.; Carr, James A.Smelting and mining sites create local contaminated areas due to atmospheric release and deposition of metals and by increasing metal-enriched soil runoff. One of the proposed mechanisms of amphibian declines is contamination of habitats by chemical pollutants. Due to the number of mining and smelting sites worldwide, there is a risk to numerous amphibian populations from metal contamination. Currently, little is known about the effects of metal contaminated soil on amphibians. While it is generally understood that certain metals are highly toxic at low concentrations to most any organism, the exposure potential between organisms varies greatly. Metal uptake from soil is difficult to predict due to a complex metal-soil-water-toad relationship. Because of this complex relationship the use of models and passive sampling devices are not possible. This study consists of a series of soil exposures to toads Great Plains toads, Bufo cognatus. Each study follows the same basic design to assess metal bioaccumulation in toads housed individually on contaminated soil. The soils used in this study all came from or were created to mimic the soil conditions at the Anaconda Smelter Superfund Site, Deer Lodge County, MT, USA. The site is characterized by elevated levels of arsenic, cadmium, copper, lead, and zinc. Following their exposure, toads were tested through a series of behavioral, physiologic, and biochemical assays to asses the effects of the exposure. Between the studies, soil origin, soil temperature, size/age of the toads, and exposure duration were varied. Over the course of the studies, all metals showed increased bioaccumulation as soil metal concentration or exposure duration increased. Arsenic was not detectable in small, young-of-the-year toads. Cadmium concentrations, numerically, increased the most across each of the studies. Lead concentrations increased in most cases of increased exposure, however, variation in lead uptake in the adult toads studied was large as exposure duration increased. Zinc and copper tissue concentrations, both regulated essential metals, each increased with increasing exposure, however, zinc showed only slight to moderate increases overall. Partitioning within the body was highly variable between metals and between the studies. Overall, for juvenile toads, skin accumulated the bulk of the metals while in adults most metals accumulated in liver and kidney. One study compared the uptake of metals from soil collected at the Anaconda Smelter site to a series of spiked soils meant to mimic the ratio of metals in the Anaconda Smelter soil. Interestingly, we found that bioavailability was different between these soils, but not in the expected pattern. Cadmium and lead were both more bioavailable in the Anaconda Smelter soil than the spiked soil. Metal contaminated soil exposure had clear effects on the health of the toads. Time taken to bury was measured as a potential indicator of detecting contaminated soil avoidance, however, no differences were seen between soils. Although not consistent between each study the following endpoints were found to change in response to increasing soil metal concentration: prey orientating reflex, hop length, righting reflex, body mass, delta-aminolevulinic acid dehydratase (ALAD) activity, urine specific gravity, and mortality. Consistently across studies, organ (liver, kidney, and spleen) morphometrics did not change. It is clear, from this study and the works of others, that metal contaminated soil poses potential harm to amphibian populations. The effect of metal contaminated soil on toads can have two important ecological affects: 1) toads suffer directly from the presence of metal contaminated habitats and die, and 2) toads can accumulate metal concentrations that are then passed on via predation to other organisms in the food web. Protecting toads from metal contaminated soil is a challenge given their ability to bury deeply in the soil and their free ranging nature.Item Bioremediation of explosives in vadose zone soil using vapor phase carbon source additions(Texas Tech University, 2005-05) Radtke, Corey W.; Cobb, George P.; Anderson, Todd; Dickerson, Richard L.; Roberto, Francisco F.Explosives contamination in vadose zone soil presents difficulties in remediation. Because vadose zone contamination can extend deep into the subsurface and underneath existing buildings and utilities, excavation is often infeasible. In response, this dissertation focuses on the development and testing of a practical system to enhance the remediation of vadose zone explosives contamination. Soil at the DOE Idaho National Engineering and Environmental Laboratory field area was characterized for explosives contamination. Of the soil tested, the particulate TNT retained on a 3 mm screen contributed approximately 2000 ppm (96.4%) of the overall soil contamination, compared to the soil that passed through the sieve, which averaged 75 ppm TNT. Contributing significantly to the contamination profile, heterogeneously dispersed, and likely point sources of contamination, the particulates thereby present difficulties in estimating the extent, risk, and treatability of explosives contamination in the soil. For monitoring soil gases, a method was developed and validated using solid phase microextraction coupled with gas chromatography and mass selective detection (SPME-GCMS). The within-run precision (repeatability) was 3.5X tighter than the between-run precision (reproducibility) in the 4 days. The esters gave the best repeatability from 50 to 80 ppmv while the corresponding alcohols gave the best results at 10 to 20 ppmv. The method was applied to monitor gases in laboratory and field studies testing explosives remediation in vadose zone soil. Anaerobic and microaerobic batch and column studies using soil from the DOE Pantex Facility contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-trinitrobenzene (TNB) were performed using gaseous carbon source additions. In the anaerobic batch study, over 99 days, flasks periodically receiving headspace pulses of 330 to 570 ppmv n-propyl acetate yielded 97.5±0.3% TNB and 66.7±43.2% RDX removal. Using ethanol in place of n-propyl acetate yielded similar results. Two column studies were performed using throughputs of oxygen, nitrogen gas, and organic carbon combinations. The columns supported less robust HE degradation than the batch systems. This difference in HE degradation between batch and column work may indicate that a key factor accumulated in the headspace of batch flasks, but was continually removed in the columns.Item Characterization of soil unsaturated flow properties using steady state centrifuge methods(2014-12) Plaisted, Michael David; Zornberg, Jorge G.Three testing procedures were developed in this research to allow expeditious characterization of soil unsaturated flow properties using steady state centrifuge methods. The first testing procedure, referred to as the “instrumented” procedure, focuses on using in-flight measurement of the suction and volumetric water content of soil samples under centrifugation. The measurements are used to calculate the soil water retention curve and hydraulic conductivity function (K-function) of soil samples. A good agreement was found between results determined using the “instrumented” procedure and standard testing methods. Several possible sources of inaccuracy were determined with the “instrumented” procedure. The void ratio, the changes of which were not measured, was found to decrease during centrifugation and the lower boundary condition, which was not accounted for in the evaluation, was found to affect a large portion of the sample. In order to improve the accuracy of results, two additional testing procedures were developed that accounted for these issues and incorporated the void ratio of the soil as an additional variable. The first additional procedure was used to measure the soil water retention surface (SWRS) of soil samples while the second was used to measure the unsaturated hydraulic conductivity surface (K-surface) of soil samples. Both new procedures, referred to as the “hydrostatic” and “imposed flow” procedures, were used to characterize the unsaturated flow properties of a low plasticity clay (“RMA” soil). The unsaturated flow characteristics of the RMA soil were evaluated for a wide range of void ratio and three compaction moisture conditions. As a result, the effects of void ratio and compaction moisture content on the unsaturated flow characteristics could be determined for the RMA soil. The compaction water content was shown to have significant effects on both the retention behavior and the unsaturated hydraulic conductivity of the RMA soil. In general, increases in compaction water content resulted in a decrease of large pore sizes in the soil, resulting in higher water retention and lower unsaturated hydraulic conductivity. The void ratio was found to have comparatively lesser, but still significant, effects on both retention and conductivity characteristics. Specifically, decreases in void ratio were shown to reduce the unsaturated hydraulic conductivity. In addition, decreases in void ratio were shown to result in either increases or decreases on the soil water retention, depending on the level of suction in the soil. A good agreement was found between results obtained using standard methods and those from the hydrostatic and imposed flow procedures. Accordingly, steady state centrifuge methods were ultimately found to provide a both expeditious and accurate method for characterizing the unsaturated flow properties of soil.Item Conservation engineering and agricultural terracing in Tlaxcala, Mexico(2014-05) LaFevor, Matthew Cole; Doolittle, William EmeryThis research examines the practice of hillslope terracing in the state of Tlaxcala, Mexico. It explores how one popular terrace form, zanja-bordo (ditch-and-border) terraces, is employed in two distinct, though sometimes related contexts: (1) producing crops (agriculture) and (2) protecting natural resources (conservation). It first traces the use of zanja-bordo terraces in traditional agriculture in the region, highlighting some of the major elements of their form and function, issues surrounding their antiquity, and their possible role in the landscape degradation so prevalent in the region today. Moving from this agricultural context, the dissertation next examines the role of zanja-bordo terraces in landscape restoration efforts in Tlaxcala. It demonstrates the key role that active and prolonged maintenance plays in long-term efforts to restore previously degraded farmland back to productive capacity. The dissertation then examines more broadly how government programs to promote zanja-bordo terracing in the region impact farmers, whose ancestors have been building zanja-bordo terraces for centuries. Findings from the collection, synthesis, analysis, and groundtruthing of written data on governmental terracing projects in the state reveal that while perhaps well intentioned, these programs did little to promote sustainable agricultural development or environmental conservation in the region. Finally, the dissertation moves above the 3,000-meter mark to examine the relatively recent phenomenon of high-elevation terracing in Mexico's national parks. Conceived as a means of erosion mitigation, water conservation, reforestation, and even fire suppression, government agencies now construct zanja-bordo terraces throughout the understory of many of Mexico's subalpine forests. A case study of the la Malinche (Malintzi or Matlalcueyatl) National Protected Area illustrates some of the difficulties in examining each of the claimed benefits of terracing in these environments. Whether for agriculture or restoration, as a techno-developmental strategy, or as a tool for soil and water conservation, zanja-bordo terraces are shown to be an adaptable and effective hillslope management technology. This dissertation demonstrates, however, that successful adaptation and implementation of zanja-bordo technologies into different contexts largely depends on the effective planning, monitoring, and maintenance of terrace structures and processes. Ultimately, the sustainability of zanja-bordo terracing relates more to issues of contextualization and human motivation than to questions of technological innovation.Item Distribution and Formation of Two Calcareous soils on the southern high plains of Texas(2008-05) Clark, Charles Wayne; Hudnall, Wayne H.; Allen, Bonnie L.; Mulligan, KevinA distinct taxonomical difference was recognized within the Estacado mapping unit on the Southern High Plains (SHP), in MLRA (Major Land Resource Area) 77C. The difference recognized prompted an investigation on whether or not a new soil series needed to be added to the legend of many counties on the SHP. The potential new soil, the Bovina series, will be identified and separated from the Estacado soil. The Estacado series is classified as Fine-loamy, mixed, superactive, thermic Aridic Paleustolls, and the proposed Bovina series is classified as Fine-loamy, mixed, superactive, thermic Calcidic Paleustolls. The primary characteristic of interest is the depth to calcic horizon (horizon with 15 percent or more secondary carbonate). The concept of the Bovina series is the same as the Estacado soil except the calcic horizon is shallower than 60 cm, while the Estacado series has a calcic horizon deeper than 60 cm. Taxonomically, it has also been observed that the particle size control section is also a factor, because many soils mapped Fine-loamy border fine and fine-silty. Progressing from southwest to northeast across the SHP, the particle size control section become fine and fine-silty rather than fine-loamy, due to the general fining in this direction. The interpretations between these two soils differ greatly. The Bovina soil would be considered HEL (Highly Erodible Land), because of the shallow calcic horizon. This means it would be considered first for government conservation programs such as CRP (Conservation Reserve Program) and EQUIP (Environmental Quality Incentive Program). Landscape relationships are fundamental to understand soil formation, distribution and occurrence. A study was conducted on two calcareous soils on the SHP of Texas to better understand and predict their occurrence and variability across the landscape. Physical, chemical, mineralogical, morphological and characteristics were used as tools in addition to GIS (Geographic Information Systems) mapping. GIS was used to examine landscape relationships, such as depth to the calcic horizon. Sand/silt ratios, clay mineralogy, and carbonate percentages were used to study the lithology.Item Dynamic properties of fine liquefiable sand and calcareous sand from resonant column testing(2015-05) Wang, Yaning, Ph. D.; Stokoe, Kenneth H.; Cox, Brady R.The study of the dynamic properties of two specific kinds of granular soils is performed using torsional resonant column testing. The sandy soils are: (1) liquefiable sand from Christchurch, New Zealand, and (2) calcareous sand from Puerto Rico. The effects of isotropic effective confining pressure, shear strain amplitude, void ratio, and total unit weight on the small-strain and nonlinear dynamic properties of both types of sand are presented and discussed. Empirical models from previous studies are examined to determine how well the models fit the test results.Item Dynamics of Soil Aggregation, Organic Carbon Pools, and Greenhouse Gases in Integrated Crop-Livestock Agroecosystems in the Texas High Plains(2012-08) Fultz, Lisa; Moore-Kucera, Jennifer; Cox, Robert D.; Maas, Stephan J.; Schwilk, Dylan W.; Zobeck, Ted M.In the Texas High Plains (THP), marked by limited water availability and low soil fertility, management (i.e. tillage, irrigation, crop selection) has great potential to impact soil quality factors, in particular soil organic matter (SOM) and carbon (SOC), and in turn the global C cycle. Soil organic C in whole soil and physically isolated pools can be indicative of a soil’s potential for C sequestration and changes due to management. Measurement of greenhouse gas (GHG) fluxes (CO2 and N2O), can provide insight into soil microbial activity, and allow for tracing losses of SOC. Further analysis of C functional groups using mid-infrared (MidIR) Fourier Transform spectroscopy, a recently (~20 years) developed method, can allow for classification of the C within aggregate fractions. Combination of these methods can provide a detailed outlook of the C interactions and response to management practices in semi-arid systems. The purpose of this research was to thoroughly examine the impacts of alternative agroecosystems on SOC as it relates to aggregation and contributions to GHG concentrations. Conventional production in this area typically consists of continuous cotton (CTN), although the implementation of alternative agroecosystem management practices such as integrated crop-livestock (ICL) systems is growing. Studied systems ranged from those established in 1997 to 2007 and represented various management practices. Specifically, seven systems were selected for monitoring of soil quality factors including mean weight diameter (MWD), aggregate proportions and SOC content, and total nitrogen (TN) content. Additionally, two systems were also utilized for monitoring of GHG fluxes. To examine these changes soil analysis was done at the whole soil level as well as within free aggregates (Elliott, 1986) and intra-aggregate (Six et al., 2000) fractions using physical dispersion. Stability of SOC was examined using the novel technique, MidIR spectroscopy, which can be used to identify C functional groups. Measurements of soil GHG fluxes, specifically CO2 and N2O, were done to aid in the estimation of the global warming potential in these semi-arid systems. Chapters 2 and 3 focus on the impacts of land management practices, including conventional and alternative agroecosystems, in seven systems located in the THP. Chapter 2 examines the changes over time as well as the differences between an ICL and conventional CTN system. Significant increases in SOC were measured within the ICL system, while no significant change was measured in the CTN. In general, MWD and SOC was greatest in systems which utilized alternative management practices (i.e. no-till, perennial vegetation, rotational cropping). Chapter 3 examined the impacts of multiple agroecosystems and associated vegetation components on SOC, aggregate stability, and nutrient content. The complexity of the systems made determination of distinctive impacts difficult. However, similar to the findings in Chapter 2, alternative management techniques resulted in increased SOC content and mean weight diameter. Chapter 4 focuses on fluxes of GHG from two of the systems identified in Chapter 3. This chapter compares fluxes of CO2 and N2O from five vegetation components managed as either irrigated or dryland systems. It was determined that perennial vegetation management resulted in significantly greater fluxes of CO2. In the case of N2O, fluxes were episodic and greatest in bermudagrass, following significant rainfall events but did not contribute significantly to global warming potential. Soil moisture, temperature, and SOC content were the major driving factors for GHG emissions. Chapter 5 examines the use of MidIR to characterize C functional groups from aggregates obtained in Chapter 2. Analysis indicates that SOC within intra-aggregate particulate organic matter was significantly different from all remaining fractions and that further separation based on C functional groups was possible in the intra-aggregate particulate organic matter and silt+clay fractions. The level of degradation associated with the intra-aggregate microaggregate fraction resulted in no significant difference in absorbance spectrum based on vegetation management. Chapter 6 compares the fractionation process when done on field-moist soils (for DNA extraction) and air-dried soils (for SOC analysis). Significant correlation was measured in fractions which produced significantly different results due to pre-fractionation conditions. This correlation may be improved by the inclusion of soil moisture at time of sampling and allow for the estimation of water stable aggregates using fractionation of field-moist soils.Item Ecological mechanisms underlying soil microbial responses to climate change(2013-12) Waring, Bonnie Grace; Hawkes, Christine V.Soil microbes influence the global carbon cycle via their role in the decomposition and formation of soil organic matter. Thus, rates of ecosystem processes such as primary production, soil respiration, and pedogenesis are sensitive to changes in the aggregate functional traits of the entire microbial community. To predict the magnitude and direction of microbial feedbacks on climate change, it is necessary to identify the physiological, ecological, and evolutionary mechanisms that underlie microbes’ responses to altered temperature and rainfall. Therefore, I examined microbial community composition and function in relation to manipulations of resource availability and precipitation in two contrasting ecosystems: a tropical rainforest at La Selva Biological Station, Costa Rica, and a semi-arid grassland in central Texas. I conducted a leaf litter decomposition experiment at La Selva to identify the physiological constraints on microbial allocation to extracellular enzymes, which degrade organic matter. I found strong evidence that microbial enzyme production is decoupled from foliar stoichiometry, consistent with weak links between leaf litter nutrients and decomposition rates at the pan-tropical scale. Next, to examine whether ecological trade-offs within microbial communities may drive shifts in carbon cycling at local spatial scales, I quantified changes in soil fungal and bacterial community composition in response to an in situ precipitation exclusion experiment I established at La Selva. Although drought-induced shifts in community structure were small, large increases in biomass-specific respiration rates were observed under dry conditions. These findings suggest that physiological adjustments to drought may constitute an important feedback on climate change in wet tropical forests. Finally, I focused on microbial community responses to climate change within a meta-community framework, using a reciprocal transplant experiment to investigate how dispersal shapes bacterial community structure along a natural rainfall gradient in central Texas. I found that soils from the wet end of the precipitation gradient exhibited more plastic functional responses to altered water availability. However, soil bacterial community composition was resistant to changes in rainfall and dispersal, preventing functional acclimatization to precipitation regime. Together, the results of these experiments emphasize the potential for physiological plasticity or microevolutionary shifts within microbial populations to drive ecosystem carbon cycling under climate change.Item Effects of long-term metal contamination on the structure and function of microbial communities in soils.(Texas Tech University, 2007-08) Humphries, Jennifer A.; Cox, Stephen B.; Zak, John; Hooper, Michael J.; Anderson, ToddMicrobial communities are critical components of soils and are known to be important for a wide range of ecosystem-level processes. However, due in part to methodological limitations, much of the basic structure and activity of microbial communities in both pristine and anthropogenically disturbed soils remains unknown. One hundred years of mining and smelting activity at the Anaconda Smelter Site in Anaconda, Montana has caused high concentrations of metals to be deposited in surrounding areas, leading to significant degradation of the soils, loss of above-ground vegetation and toxicological effects on humans and wildlife. Different phytoremediation strategies were tested in situ within the 1.5 acre Dragstrip demonstration area, to assess the efficacy of different soil amendments (fertilizer formulations, organic matter, liming materials, and depth of soil plowing) for supporting plant growth. The success of plant-based remediation techniques is largely dependent on the health and stability of the soil, of which soil microbial communities play essential roles. While high concentrations of metals are known to negatively affect microbial activity, biomass, and enzyme function, amendment of soils during the remediation process may further modify microbial community structure and function in soils. Little is known about the effects of soil amendments on the structural and functional diversity of microbial communities in heavy metal contaminated soils. Additionally, a better understanding is needed of the effects of metals on microbial community structure and function following long-term in sutu exposure, and following contamination with increasing concentrations of metals. The following research attempts to characterize the effects of anthropogenic disturbance (i.e., soil metal contamination and/or different soil amendment strategies) on the structure and function of microbial communities in soils surrounding the Anaconda Smelter as follows: 1) Microbial communities within the six remediated Dragstrip demonstration plots and adjacent unremediated control plot were characterized using a combination of culture-based (Biolog) and non-culture based (DGGE) techniques to characterize the combined effects of soil metal contamination and amendment strategy on microbial community structural (community DGGE banding profiles) and functional diversity (community carbon substrate utilization profiles (SUPs)). 2) Microbial communities native to six smelter-impacted sites (representing a gradient of soil metal concentrations) and a non-impacted site (representing background levels of metals) were compared to determine the long-term effects of metal contamination on microbial community dynamics (microbial activity, biomass, structural diversity and functional diversity). 3) Soil native to two smelter-impacted sites and a non-impacted site (previously exposed to high, low or background concentrations of aerially-deposited metals, in situ, respectively) were artificially-amended with metal-salts in the laboratory to characterize the dose-response effects of increasing concentrations of metals on microbial community dynamics. Additionally, this research tested the hypothesis that soil metal contamination, acting as an extreme environmental stressor, will catalyze a shift in species diversity and abundance, causing initially unique communities to converge on a community with similar structure and function. Results from these studies show that several physiochemical soil characteristics (percent organic matter, soil pH, cation exchange capacity) significantly influence the bioavailability of metals in soils, and metal bioavailability in turn influenced the toxicity of metals to soil microbes. Not only did soil metals significantly decrease microbial activity and biomass, but they also caused significant shifts in community structure, indicating the potential for metal stress to shift species diversity and abundance. The effects of soil metal contamination on community SUPs was less pronounced, which may give evidence of functional redundancy within the enriched portion of the communities. Soil physiochemical profiles were influenced by soil remediation amendment strategies, and several physiochemical parameters (K, NH4organic matter, and cation exchange capacity) were correlated with shifts in microbial community structure, indicating that amendment strategy has the potential to modify microbial communities over time. Finally, while microbial communities were not observed to converge on a common community as a result metal stress, these studies have documented the potential for metal contamination to shape the structural and functional diversity of microbial communities in soils. Microbial community endpoints are increasingly being marketed as potentially good indicators of soil ecosystem health and stability. These studies have shown that microbial community activity, biomass, community structure, and community function are sensitive endpoints for monitoring microbial responses to metal stress. However, additional studies are necessary to truly understand the complexity of microbial community responses to long-term metal contamination.Item Energy Piles in Cooling Dominated Climates(2014-04-10) Akrouch, GhassanAir pollution is one of the main environmental problems mankind faces in the 21^(st) century caused by to the extensive use of fossil fuels. One of the opportunities to overcome this problem is to develop new technologies and methods to profit from the energy stored in the ground. A promising high-efficiency technology for the thermal control of buildings is the shallow geothermal energy. This technology is growing rapidly because it consumes less conventional energy for operation, which in turn results in fewer CO_(2) emissions. This technology harnesses constant and moderate ground temperature for thermal control of a building using foundation piles. Outside air temperature changes with the season, while ground temperature remains moderate and constant. In summer, ground temperature is lower than air temperature, and so the ground may be used as a heat sink. The opposite is true in winter; the ground becomes a heat source. This technology is used efficiently in cold, heating dominated climates. Could this be true in hot, cooling dominated climates? To achieve the ultimate goal and answer the above question, this study considered the different elements of a full SGES, namely: soil, climate, energy pile, and ground source heat pump. First, The need for a new, easy, and quick in-situ method to thermally characterize soils lead to the development of the Thermal Cone Test. Second, the soil-climate interaction and its effect on the thermodynamic efficiency of energy piles was an important factor to consider, where the decrease in soil saturation leads to a decrease in the heat exchange rate of energy piles. Third, the thermal use of foundation pile changes the pile and surrounding soil temperature where both materials are temperature dependent. This change in temperature leads to a change in the mechanical behavior of energy piles. Fourth, a full-scale test on installed and instrumented energy piles group was needed to understand the thermodynamics of a full system and to provide experimental data for a full economic study. Finally, this study was capped by an economic analysis to evaluate the cost, benefits, payback period, and feasibility of SGES in cooling dominated climates. The study presented in this dissertation found that integrating energy piles in heating and cooling systems in hot, cooling dominated climates could be economical and environmentally friendly solution, but attention should be paid to the thermodynamic efficiency of the system when unsaturated soil layer is encountered, and to the long term mechanical behavior of foundation piles in high plasticity clay where additional settlement could take place resulting from the increased creep rate caused by soil heating.Item INFLUENCE OF MATRIC SUCTION AND SATURATION ON COMPRESSIVE AND FLEXURAL STRENGTH OF UNSTABILIZED COMPRESSED EARTH BLOCK(2013-05) Gaikwad, Aditya; Tate, Derrick; Lawson, William D.; Bae, Sang-WookEarth materials have been used as a construction material for centuries. But systematic modern research for compressed earth dates back to the early 60’s. Compressed earth has shown to be a very durable material. This is evident from all the ancient structures, which have stood the test of time. Previous experiments with compressed earth have studied the properties of compressed earth blocks. This research builds on that knowledge to study influence of matric suction and initial moisture content on the compressive and flexural strengths of the blocks. The soil was procured from a landfill site near Lubbock international airport. Tests were performed to analyze the soil type. Blocks were then made using the compressed earth block manufacturing machine available at Texas Tech University. Experiments were carried out to study the compressive and flexural strengths of the blocks when cured in two different relative humidity conditions. These blocks were made at three different initial moisture contents. The results show an increase in compressive strength with an increase in suction. The results for the flexural strength data were different from expected, showing a decrease in flexural strength with an increase in matric suction. The change in the strength was also studied relative to the change in the suction and saturation.Item Influence of metal mixtures on co-occurring toxic metal bioavailability and effects in adult and developing deer mice(Texas Tech University, 2007-12) McBride, Tobias J.; Hooper, Michael J.; McMurry, Scott T.; Cox, Stephen B.; Hoff, Dale J.The bioaccessibility, bioavailability, and bioaccumulation of inorganic metals are complex principles. Unlike organic xenobiotics, many metals are required for biological functions. Nonetheless, dramatically increased concentrations of any metal may interact adversely with biomolecules, initiating a toxicological response when above a certain concentration in the organism. The bioavailability of environmental metals depends not only on metal concentrations in relevant matrices (food, water, soil), but on the chemical/physical form in which metals occur, the concentrations of other metals which co-occur, and the physiological status of the individual. Studies of mixed metal and metalloid (As, Cd, Cu, Pb and Zn) exposure in deer mice (Peromyscus maniculatus) at the Anaconda Smelter Site demonstrated that accumulation and biomarkers did not respond to the extent anticipated based on individual metal levels alone. This dissertation focuses on factors influencing the uptake, accumulation and resultant health effects of inorganic metals in a ubiquitous wild rodent species, and attempts to explain results from an earlier wildlife assessment on an NPL Superfund site. We sought to explain the variability in the effects of Pb exposure seen with the extreme heterogeneity of co-occurring metal contaminants in site soils. Using soil feeding studies, we have dissected the roles of Cu and Zn in modulating Pb absorption and Zn's role in reactivating ALAD activity in mice receiving high Pb doses. Second, our focus involves a lifetime bioaccumulation study of mice that investigated lactational metal exposure through the first 21 days of life (from soil-dosed feed provided to dams), and follows accumulation through 100 days of life. Comparisons with studies where adult mice were fed soil metals in their diet demonstrated that the more realistic lifetime exposure approach changes the accumulation kinetics, leading to greater accumulation of Cd and As, while underestimating exposures to Pb in the younger individuals. Finally, we investigate the role of lactation in weanling metal bioaccumulation, demonstrating how lactation decreases the dam's metal accumulation, while significantly increasing As and Pb exposure risks to the developing young.Item Laboratory investigation of explosives degradation in vadose zone soil using carbon source additions(2005-05) Radtke, Corey William; Cobb, George P.; Anderson, Todd A.; Dickerson, Richard L.; Roberto, Francisco F.Explosives contamination in vadose zone soil presents difficulties in remediation. Because vadose zone contamination can extend deep into the subsurface and underneath existing buildings and utilities, excavation is often infeasible. In response, this dissertation focuses on the development and testing of a practical system to enhance the remediation of vadose zone explosives contamination. Soil at the DOE Idaho National Engineering and Environmental Laboratory field area was characterized for explosives contamination. Of the soil tested, the particulate TNT retained on a 3 mm screen contributed approximately 2000 ppm (96.4%) of the overall soil contamination, compared to the soil that passed through the sieve, which averaged 75 ppm TNT. Contributing significantly to the contamination profile, heterogeneously dispersed, and likely point sources of contamination, the particulates thereby present difficulties in estimating the extent, risk, and treatability of explosives contamination in the soil. For monitoring soil gases, a method was developed and validated using solid phase microextraction coupled with gas chromatography and mass selective detection (SPME-GCMS). The within-run precision (repeatability) was 3.5X tighter than the between-run precision (reproducibility) in the 4 days. The esters gave the best repeatability from 50 to 80 ppmv while the corresponding alcohols gave the best results at 10 to 20 ppmv. The method was applied to monitor gases in laboratory and field studies testing explosives remediation in vadose zone soil. Anaerobic and microaerobic batch and column studies using soil from the DOE Pantex Facility contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-trinitrobenzene (TNB) were performed using gaseous carbon source additions. In the anaerobic batch study, over 99 days, flasks periodically receiving headspace pulses of 330 to 570 ppmv n-propyl acetate yielded 97.5±0.3% TNB and 66.7±43.2% RDX removal. Using ethanol in place of n-propyl acetate yielded similar results. Two column studies were performed using throughputs of oxygen, nitrogen gas, and organic carbon combinations. The columns supported less robust HE degradation than the batch systems. This difference in HE degradation between batch and column work may indicate that a key factor accumulated in the headspace of batch flasks, but was continually removed in the columns.Item Management system effects on water infiltration and soil physical properties(2005-05) Halfmann, Deanna M.; Zobeck, Ted M.; Zartman, Richard E.; Ramsey, Ralph H.Soil and water conservation are important issues on the Southern High Plains because of limited rainfall and windy conditions. Alternative management styles of ranching and farming may help conserve our natural resources by allowing for increased water infiltration and improving soil physical properties. The management system effects on water infiltration and soil physical properties were analyzed at two locations. A clay loam soil consisting of an integrated livestock-cropping system was analyzed near New Deal, TX. No-till dryland and irrigated cotton systems, a conventional tillage dryland cotton system, CRP, and native range were analyzed on a loamy fine sand near Wellman, TX. The testing methods included soil bulk density, soil moisture, soil penetration resistance, double-ring infiltrometers to measure water infiltration rates under saturated conditions at both sites, and tension infiltrometers to measure unsaturated hydraulic conductivity at the Wellman site. The results at New Deal indicated that the penetration resistance and bulk density are associated by depth, not management system. The penetration resistance increased with each depth, reached its maximum value at the 15 cm depth, then lowered slightly at 20 cm and remained fairly constant throughout the bottom 20 to 30 cm depth. The bulk density increased though the top 15 cm depths, and then lowered through the 15 to 30 cm depth. The water infiltration rates seemed to be independent of the penetration resistance and bulk density because the management systems with the highest resistance and bulk densities did not have the lowest infiltration rates. At the Wellman site, a trend seemed to develop among cropping systems. The native range had the lowest penetration resistance and bulk density, and the highest infiltration rate under saturated conditions. The conventional tillage dryland cotton system had the highest penetration resistance and bulk density, and the lowest infiltration rate under saturated conditions. The no-till and CRP systems seemed to fall in the middle tier for penetration resistance, bulk density, and infiltration rates. The no-till irrigated cotton and CRP systems were more comparable to the native range, while the no-till dryland cotton system was more comparable to the conventional tillage dryland cotton system.Item Simulation of ice wedge polygon geomorphic transition, Prudhoe Bay, Alaska(2015-08) Abolt, Charles Joseph; Young, Michael H.; Johnson, Joel P; Sharp, John MA numerical model is presented to simulate the changes in topography associated with ice wedge polygon transition from low-centered to high-centered form. The model applies a hillslope diffusion equation to an eroding polygon using a finite-difference approach. It is calibrated using a LiDAR dataset from a site where low-centered polygons exist within meters of high-centered polygons, whose formation appears to have been triggered by construction of the Dalton Highway. The loss of hydrologic storage and the transport of soil from the polygon center into polygon troughs during transition are estimated from model simulations. Optimized values of the hillslope diffusion coefficient suggest that multiple physical processes, including frost heave and continuous soil creep, may drive lateral soil transport at the site. The optimized parameters, furthermore, capture the decreasing influence of anthropogenic disturbances (in this case, the Dalton Highway) on polygon form at distances greater than 35 meters. Overall, a match between the topography of simulated and observed high-centered polygons confirms that the hillslope diffusion paradigm approximates much of the complexity of polygon transition. Future refinements to the model should include more process-based treatment of the mechanisms that drive soil transport and control rates of polygon erosion.Item Soil stabilization using optimum quantity of calcium chloride with Class F fly ash(Texas A&M University, 2006-10-30) Choi, Hyung JunOn-going research at Texas A&M University indicated that soil stabilization using calcium chloride filter cake along with Class F fly ash generates high strength. Previous studies were conducted with samples containing calcium chloride filter cake and both Class C fly ash and Class F fly ash. Mix design was fixed at 1.3% and 1.7% calcium chloride and 5% and 10% fly ash with crushed limestone base material. Throughout previous studies, recommended mix design was 1.7% calcium chloride filter cake with 10% Class F fly ash in crushed limestone base because Class F fly ash generates early high and durable strength. This research paper focused on the strength increase initiated by greater than 1.7% pure calcium chloride used with Class F fly ash in soil to verify the effectiveness and optimum ratio of calcium chloride and Class F fly ash in soil stabilization. Mix design was programmed at pure calcium chloride concentrations at 0% to 6% and Class F fly ash at 10 to 15%. Laboratory tests showed samples containing any calcium chloride concentration from 2% to 6% and Class F fly ash content from 10% to 15% obtained high early strength however, optimum moisture content, different mix design, and mineralogy deposit analysis are recommended to evaluate the role and the effectiveness of calcium chloride in soil stabilization because of the strength decreasing tendency of the samples containing calcium chloride after 56 days.