Matching Items (9)
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- All Subjects: Soil moisture
- All Subjects: Expansive Soils
- Creators: Kavazanjian, Edward
- Member of: Theses and Dissertations
- Member of: Barrett, The Honors College Thesis/Creative Project Collection
Description
In a laboratory setting, the soil volume change behavior is best represented by using various testing standards on undisturbed or remolded samples. Whenever possible, it is most precise to use undisturbed samples to assess the volume change behavior but in the absence of undisturbed specimens, remodeled samples can be used. If that is the case, the soil is compacted to in-situ density and water content (or matric suction), which should best represent the expansive profile in question. It is standard practice to subject the specimen to a wetting process at a particular net normal stress. Even though currently accepted laboratory testing standard procedures provide insight on how the profile conditions changes with time, these procedures do not assess the long term effects on the soil due to climatic changes. In this experimental study, an assessment and quantification of the effect of multiple wetting/drying cycles on the volume change behavior of two different naturally occurring soils was performed. The changes in wetting and drying cycles were extreme when comparing the swings in matric suction. During the drying cycle, the expansive soil was subjected to extreme conditions, which decreased the moisture content less than the shrinkage limit. Nevertheless, both soils were remolded at five different compacted conditions and loaded to five different net normal stresses. Each sample was subjected to six wetting and drying cycles. During the assessment, it was evident from the results that the swell/collapse strain is highly non-linear at low stress levels. The strain-net normal stress relationship cannot be defined by one single function without transforming the data. Therefore, the dataset needs to be fitted to a bi-modal logarithmic function or to a logarithmic transformation of net normal stress in order to use a third order polynomial fit. It was also determined that the moisture content changes with time are best fit by non-linear functions. For the drying cycle, the radial strain was determined to have a constant rate of change with respect to the axial strain. However, for the wetting cycle, there was not enough radial strain data to develop correlations and therefore, an assumption was made based on 55 different test measurements/observations, for the wetting cycles. In general, it was observed that after each subsequent cycle, higher swelling was exhibited for lower net normal stress values; while higher collapse potential was observed for higher net normal stress values, once the net normal stress was less than/greater than a threshold net normal stress value. Furthermore, the swelling pressure underwent a reduction in all cases. Particularly, the Anthem soil exhibited a reduction in swelling pressure by at least 20 percent after the first wetting/drying cycle; while Colorado soil exhibited a reduction of 50 percent. After about the fourth cycle, the swelling pressure seemed to stabilized to an equilibrium value at which a reduction of 46 percent was observed for the Anthem soil and 68 percent reduction for the Colorado soil. The impact of the initial compacted conditions on heave characteristics was studied. Results indicated that materials compacted at higher densities exhibited greater swell potential. When comparing specimens compacted at the same density but at different moisture content (matric suction), it was observed that specimens compacted at higher suction would exhibit higher swelling potential, when subjected to the same net normal stress. The least amount of swelling strain was observed on specimens compacted at the lowest dry density and the lowest matric suction (higher water content). The results from the laboratory testing were used to develop ultimate heave profiles for both soils. This analysis showed that even though the swell pressure for each soil decreased with cycles, the amount of heave would increase or decrease depending upon the initial compaction condition. When the specimen was compacted at 110% of optimum moisture content and 90% of maximum dry density, it resulted in an ultimate heave reduction of 92 percent for Anthem and 685 percent for Colorado soil. On the other hand, when the soils were compacted at 90% optimum moisture content and 100% of the maximum dry density, Anthem specimens heave 78% more and Colorado specimens heave was reduced by 69%. Based on the results obtained, it is evident that the current methods to estimate heave and swelling pressure do not consider the effect of wetting/drying cycles; and seem to fail capturing the free swell potential of the soil. Recommendations for improvement current methods of practice are provided.
ContributorsRosenbalm, Daniel Curtis (Author) / Zapata, Claudia E (Thesis advisor) / Houston, Sandra L. (Committee member) / Kavazanjian, Edward (Committee member) / Witczak, Mathew W (Committee member) / Arizona State University (Publisher)
Created2013
Description
Unsaturated soil mechanics is becoming a part of geotechnical engineering practice, particularly in applications to moisture sensitive soils such as expansive and collapsible soils and in geoenvironmental applications. The soil water characteristic curve, which describes the amount of water in a soil versus soil suction, is perhaps the most important soil property function for application of unsaturated soil mechanics. The soil water characteristic curve has been used extensively for estimating unsaturated soil properties, and a number of fitting equations for development of soil water characteristic curves from laboratory data have been proposed by researchers. Although not always mentioned, the underlying assumption of soil water characteristic curve fitting equations is that the soil is sufficiently stiff so that there is no change in total volume of the soil while measuring the soil water characteristic curve in the laboratory, and researchers rarely take volume change of soils into account when generating or using the soil water characteristic curve. Further, there has been little attention to the applied net normal stress during laboratory soil water characteristic curve measurement, and often zero to only token net normal stress is applied. The applied net normal stress also affects the volume change of the specimen during soil suction change. When a soil changes volume in response to suction change, failure to consider the volume change of the soil leads to errors in the estimated air-entry value and the slope of the soil water characteristic curve between the air-entry value and the residual moisture state. Inaccuracies in the soil water characteristic curve may lead to inaccuracies in estimated soil property functions such as unsaturated hydraulic conductivity. A number of researchers have recently recognized the importance of considering soil volume change in soil water characteristic curves. The study of correct methods of soil water characteristic curve measurement and determination considering soil volume change, and impacts on the unsaturated hydraulic conductivity function was of the primary focus of this study. Emphasis was placed upon study of the effect of volume change consideration on soil water characteristic curves, for expansive clays and other high volume change soils. The research involved extensive literature review and laboratory soil water characteristic curve testing on expansive soils. The effect of the initial state of the specimen (i.e. slurry versus compacted) on soil water characteristic curves, with regard to volume change effects, and effect of net normal stress on volume change for determination of these curves, was studied for expansive clays. Hysteresis effects were included in laboratory measurements of soil water characteristic curves as both wetting and drying paths were used. Impacts of soil water characteristic curve volume change considerations on fluid flow computations and associated suction-change induced soil deformations were studied through numerical simulations. The study includes both coupled and uncoupled flow and stress-deformation analyses, demonstrating that the impact of volume change consideration on the soil water characteristic curve and the estimated unsaturated hydraulic conductivity function can be quite substantial for high volume change soils.
ContributorsBani Hashem, Elham (Author) / Houston, Sandra L. (Thesis advisor) / Kavazanjian, Edward (Committee member) / Zapata, Claudia (Committee member) / Arizona State University (Publisher)
Created2013
Description
The importance of unsaturated soil behavior stems from the fact that a vast majority of infrastructures are founded on unsaturated soils. Research has recently been concentrated on unsaturated soil properties. In the evaluation of unsaturated soils, researchers agree that soil water retention characterized by the soil water characteristic curve (SWCC) is among the most important factors when assessing fluid flow, volume change and shear strength for these soils. The temperature influence on soil moisture flow is a major concern in the design of important engineering systems such as barriers in underground repositories for radioactive waste disposal, ground-source heat pump (GSHP) systems, evapotranspirative (ET) covers and pavement systems.. Accurate modeling of the temperature effect on the SWCC may lead to reduction in design costs, simpler constructability, and hence, more sustainable structures. . The study made use of two possible approaches to assess the temperature effect on the SWCC. In the first approach, soils were sorted from a large soil database into families of similar properties but located on sites with different MAAT. The SWCCs were plotted for each family of soils. Most families of soils showed a clear trend indicating the influence of temperature on the soil water retention curve at low degrees of saturation.. The second approach made use of statistical analysis. It was demonstrated that the suction increases as the MAAT decreases. The statistical analysis showed that even though the plasticity index proved to have the greatest influence on suction, the mean annual air temperature effect proved not to be negligible. In both approaches, a strong relationship between temperature, suction and soil properties was observed. Finally, a comparison of the model based on the mean annual air temperature environmental factor was compared to another model that makes use of the Thornthwaite Moisture Index (TMI) to estimate the environmental effects on the suction of unsaturated soils. Results showed that the MAAT can be a better indicator when compared to the TMI found but the results were inconclusive due to the lack of TMI data available.
ContributorsElkeshky, Maie Mohamed (Author) / Zapata, Claudia E (Thesis advisor) / Houston, Sandra (Committee member) / Kavazanjian, Edward (Committee member) / Arizona State University (Publisher)
Created2011
Description
In geotechnical engineering, measuring the unsaturated hydraulic conductivity of fine grained soils can be time consuming and tedious. The various applications that require knowledge of the unsaturated hydraulic conductivity function are great, and in geotechnical engineering, they range from modeling seepage through landfill covers to determining infiltration of water under a building slab. The unsaturated hydraulic conductivity function can be measured using various direct and indirect techniques. The instantaneous profile method has been found to be the most promising unsteady state method for measuring the unsaturated hydraulic conductivity function for fine grained soils over a wide range of suction values. The instantaneous profile method can be modified by using different techniques to measure suction and water content and also through the way water is introduced or removed from the soil profile. In this study, the instantaneous profile method was modified by creating duplicate soil samples compacted into cylindrical tubes at two different water contents. The techniques used in the duplicate method to measure the water content and matric suction included volumetric moisture probes, manual water content measurements, and filter paper tests. The experimental testing conducted in this study provided insight into determining the unsaturated hydraulic conductivity using the instantaneous profile method for a sandy clay soil and recommendations are provided for further evaluation. Overall, this study has demonstrated that the presence of cracks has no significant impact on the hydraulic behavior of soil in high suction ranges. The results of this study do not examine the behavior of cracked soil unsaturated hydraulic conductivity at low suction and at moisture contents near saturation.
ContributorsJacquemin, Sean Christopher (Author) / Zapata, Claudia (Thesis advisor) / Houston, Sandra (Committee member) / Kavazanjian, Edward (Committee member) / Arizona State University (Publisher)
Created2011
Description
The influence of temperature on soil engineering properties is a major concern in the design of engineering systems such as radioactive waste disposal barriers, ground source heat pump systems and pavement structures. In particular, moisture redistribution under pavement systems might lead to changes in unbound material stiffness that will affect pavement performance. Accurate measurement of thermal effects on unsaturated soil hydraulic properties may lead to reduction in design and construction costs. This thesis presents preliminary results of an experimental study aimed at determining the effect of temperature on the soil water characteristic curve (SWCC) and the unsaturated hydraulic conductivity function (kunsat). Pressure plate devices with volume change control were used to determine the SWCC and the instantaneous profile method was used to obtain the kunsat function. These properties were measured on two fine-grained materials subjected to controlled temperatures of 5oC, 25oC and 40oC. The results were used to perform a sensitivity analysis of the effect of temperature changes on the prediction of moisture movement under a covered area. In addition, two more simulations were performed where changes in hydraulic properties were done in a stepwise fashion. The findings were compared to field measured water content data obtained on the subgrade material of the FAA William Hughes test facility located in Atlantic City. Results indicated that temperature affects the unsaturated hydraulic properties of the two soils used in the study. For the DuPont soil, a soil with high plasticity, it was found that the water retention was higher at low temperatures for suction levels lower than about 10,000 kPa; while the kunsat functions at the three temperatures were not significantly different. For the County soil, a material with medium plasticity, it was found that it holds around 10% more degree of saturation at 5°C than that at 40°C for suction levels higher than about 1,000 kPa; while the hydraulic conductivity at 40°C was at least one order of magnitude higher than that at 5°C, for suction levels higher than 1,000 kPa. These properties were used to perform two types of numerical analyses: a sensitivity analysis and stepwise analysis. Absolute differences between predicted and field measured data were considered to be acceptable, ranging from 4.5% to 9% for all simulations. Overall results show an improvement in predictions when non-isothermal conditions were used over the predictions obtained with isothermal conditions.
ContributorsLu, Yutong (Author) / Zapata, Claudia E (Thesis advisor) / Kavazanjian, Edward (Committee member) / Houston, Sandra L. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Expansive soils in the United States cause extensive damage to roadways, buildings, and various structures. There are several treatment or methods of mitigation for these expansive soils. These treatments can be physical or chemical treatments that serve to provide more suitable building qualities for foundations and roadways alike. The main issue with expansive soils, is the volumetric variations, which are known as swelling and consolidation. These behaviors of the soil are usually stabilized through the use of lime solution, Portland Cement Concrete, and a newer technology in chemical treatments, sodium silicate solutions. Although the various chemical treatments show benefits in certain areas, the most beneficial method for stabilization comes from the combination of the chemical treatments. Lime and Portland cement concrete are the most effective in terms of increasing compressive strength and reduction of swell potential. However, with the introduction of silicate into either treatment, the efficacy of the treatments increases by a large amount lending itself more as an additive for the former processes. Sodium silicate solution does not lend itself to effectively increase the compressive strength of expansive soils. The sodium silicate solution treatment needs extensive research and development to further improve the process. A proposed experiment plan has been recommended to develop trends of pH and temperature and its influence on the effectiveness of the treatment. Nonetheless, due to the high energy consumption of the other processes, sodium silicate solution may be a proper step in decreases the carbon footprint, that is currently being created by the synthesis of Portland Cement Concrete and lime.
ContributorsMeza, Magdaleno (Author) / Zapata, Claudia (Thesis director) / Kavazanjian, Edward (Committee member) / Civil, Environmental and Sustainable Eng Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2018-12
Description
Currently conventional Subtitle D landfills are the primary means of disposing of our waste in the United States. While this method of waste disposal aims at protecting the environment, it does so through the use of liners and caps that effectively freeze the breakdown of waste. Because this method can keep landfills active, and thus a potential groundwater threat for over a hundred years, I take an in depth look at the ability of bioreactor landfills to quickly stabilize waste. In the thesis I detail the current state of bioreactor landfill technologies, assessing the pros and cons of anaerobic and aerobic bioreactor technologies. Finally, with an industrial perspective, I conclude that moving on to bioreactor landfills as an alternative isn't as simple as it may first appear, and that it is a contextually specific solution that must be further refined before replacing current landfills.
ContributorsWhitten, George Avery (Author) / Kavazanjian, Edward (Thesis director) / Allenby, Braden (Committee member) / Houston, Sandra (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / Barrett, The Honors College (Contributor)
Created2013-05
Description
The presence of expansive soils underneath pavement structures is considered one of the most common sources of pavement distresses, due to differential settlements caused by differential moisture distribution attributed to soil heterogeneity and seasonal climatic fluctuations. The cost of the repairs to the infrastructure caused by expansive soils is estimated to exceed 10 billion dollars annually in the US, as reported by Puppala and Cerato (2009). Although many studies have been developed to better understand the volume change of unsaturated soils and incorporate the effect of swelling/shrinkage behavior into pavement design procedures, current methodologies are still based on simple correlations with index properties or other empirical methods. Such solutions lead to poor or uneconomical design practices. The objective of this study was to calibrate and implement a new mechanistic, stochastic model that predicts pavement distresses caused by the presence of expansive soils. Three major tasks were completed to fulfill the objective of this study: 1) a laboratory research program performed to estimate the volume change of compacted specimens, with different expansion potential, due to the simultaneous application of suction and net normal stresses, 2) the calibration of a new mechanistic free-swell model for expansive soils tailored to pavement structures, based on elevation information collected from the Long Term Pavement Performance (LTPP) program, and 3) the incorporation and calibration of the free-swell stochastic model results into the current Pavement Mechanistic-Empirical (ME) Design procedure using the International Roughness Index (IRI) models.
The results presented includes: 1) an empirical model to estimate volume change due to the coupled effect of suction, and net normal stresses, for soils with different soil index properties, 2) a calibrated model to adjust the free-swell results of the mechanistic-stochastic model developed by Olaiz et al. (2021), and 3) an updated IRI equation for asphalt concrete pavements to account for volume change fluctuations due to changes in suction stress conditions. The models presented can be easily implemented into currently available pavement design procedures and greatly improves over the existing empirical models that have been used for more than four decades.
ContributorsMosawi, Mohammad (Author) / Zapata, Claudia E (Thesis advisor) / Kavazanjian, Edward (Committee member) / Kaloush, Kamil E (Committee member) / Arizona State University (Publisher)
Created2022
Description
Zero-Valent Metals (ZVM) are highly reactive materials and have been proved to be effective in contaminant reduction in soils and groundwater remediation. In fact, zero-Valent Iron (ZVI) has proven to be very effective in removing, particularly chlorinated organics, heavy metals, and odorous sulfides. Addition of ZVI has also been proved in enhancing the methane gas generation in anaerobic digestion of activated sludge. However, no studies have been conducted regarding the effect of ZVM stimulation to Municipal Solid Waste (MSW) degradation. Therefore, a collaborative study was developed to manipulate microbial activity in the landfill bioreactors to favor methane production by adding ZVMs. This study focuses on evaluating the effects of added ZVM on the leachate generated from replicated lab scale landfill bioreactors. The specific objective was to investigate the effects of ZVMs addition on the organic and inorganic pollutants in leachate. The hypothesis here evaluated was that adding ZVM including ZVI and Zero Valent Manganese (ZVMn) will enhance the removal rates of the organic pollutants present in the leachate, likely by a putative higher rate of microbial metabolism. Test with six (4.23 gallons) bioreactors assembled with MSW collected from the Salt River Landfill and Southwest Regional Landfill showed that under 5 grams /liter of ZVI and 0.625 grams/liter of ZVMn additions, no significant difference was observed in the pH and temperature data of the leachate generated from these reactors. The conductivity data suggested the steady rise across all reactors over the period of time. The removal efficiency of sCOD was highest (27.112 mg/lit/day) for the reactors added with ZVMn at the end of 150 days for bottom layer, however the removal rate was highest (16.955 mg/lit/day) for ZVI after the end of 150 days of the middle layer. Similar trends in the results was observed in TC analysis. HPLC study indicated the dominance of the concentration of heptanoate and isovalerate were leachate generated from the bottom layer across all reactors. Heptanoate continued to dominate in the ZVMn added leachate even after middle layer injection. IC analysis concluded the chloride was dominant in the leachate generated from all the reactors and there was a steady increase in the chloride content over the period of time. Along with chloride, fluoride, bromide, nitrate, nitrite, phosphate and sulfate were also detected in considerable concentrations. In the summary, the addition of the zero valent metals has proved to be efficient in removal of the organics present in the leachate.
ContributorsPandit, Gandhar Abhay (Author) / Cadillo – Quiroz, Hinsby (Thesis advisor) / Olson, Larry (Thesis advisor) / Boyer, Treavor (Committee member) / Arizona State University (Publisher)
Created2019