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- All Subjects: Soils
- All Subjects: Soil moisture
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- Creators: Houston, Sandra
- Resource Type: Text
Description
The effect of earthquake-induced liquefaction on the local void ratio distribution of cohesionless soil is evaluated using x-ray computed tomography (CT) and an advanced image processing software package. Intact, relatively undisturbed specimens of cohesionless soil were recovered before and after liquefaction by freezing and coring soil deposits created by pluviation and by sedimentation through water. Pluviated soil deposits were liquefied in the small geotechnical centrifuge at the University of California at Davis shared-use National Science Foundation (NSF)-supported Network for Earthquake Engineering Simulation (NEES) facility. A soil deposit created by sedimentation through water was liquefied on a small shake table in the Arizona State University geotechnical laboratory. Initial centrifuge tests employed Ottawa 20-30 sand but this material proved to be too coarse to liquefy in the centrifuge. Therefore, subsequent centrifuge tests employed Ottawa F60 sand. The shake table test employed Ottawa 20-30 sand. Recovered cores were stabilized by impregnation with optical grade epoxy and sent to the University of Texas at Austin NSF-supported facility at the University of Texas at Austin for high-resolution CT scanning of geologic media. The local void ratio distribution of a CT-scanned core of Ottawa 20-30 sand evaluated using Avizo® Fire, a commercially available advanced program for image analysis, was compared to the local void ratio distribution established on the same core by analysis of optical images to demonstrate that analysis of the CT scans gave similar results to optical methods. CT scans were subsequently conducted on liquefied and not-liquefied specimens of Ottawa 20-30 sand and Ottawa F60 sand. The resolution of F60 specimens was inadequate to establish the local void ratio distribution. Results of the analysis of the Ottawa 20-30 specimens recovered from the model built for the shake table test showed that liquefaction can substantially influence the variability in local void ratio, increasing the degree of non-homogeneity in the specimen.
ContributorsGutierrez, Angel (Author) / Kavazanjian, Edward (Thesis advisor) / Houston, Sandra (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
A method for evaluating the integrity of geosynthetic elements of a waste containment system subject to seismic loading is developed using a large strain finite difference numerical computer program. The method accounts for the effect of interaction between the geosynthetic elements and the overlying waste on seismic response and allows for explicit calculation of forces and strains in the geosynthetic elements. Based upon comparison of numerical results to experimental data, an elastic-perfectly plastic interface model is demonstrated to adequately reproduce the cyclic behavior of typical geomembrane-geotextile and geomembrane-geomembrane interfaces provided the appropriate interface properties are used. New constitutive models are developed for the in-plane cyclic shear behavior of textured geomembrane/geosynthetic clay liner (GMX/GCL) interfaces and GCLs. The GMX/GCL model is an empirical model and the GCL model is a kinematic hardening, isotropic softening multi yield surface plasticity model. Both new models allows for degradation in the cyclic shear resistance from a peak to a large displacement shear strength. The ability of the finite difference model to predict forces and strains in a geosynthetic element modeled as a beam element with zero moment of inertia sandwiched between two interface elements is demonstrated using hypothetical models of a heap leach pad and two typical landfill configurations. The numerical model is then used to conduct back analyses of the performance of two lined municipal solid waste (MSW) landfills subjected to strong ground motions in the Northridge earthquake. The modulus reduction "backbone curve" employed with the Masing criterion and 2% Rayleigh damping to model the cyclic behavior of MSW was established by back-analysis of the response of the Operating Industries Inc. landfill to five different earthquakes, three small magnitude nearby events and two larger magnitude distant events. The numerical back analysis was able to predict the tears observed in the Chiquita Canyon Landfill liner system after the earthquake if strain concentrations due to seams and scratches in the geomembrane are taken into account. The apparent good performance of the Lopez Canyon landfill geomembrane and the observed tension in the overlying geotextile after the Northridge event was also successfully predicted using the numerical model.
ContributorsArab, Mohamed G (Author) / Kavazanjian, Edward (Thesis advisor) / Zapata, Claudia (Committee member) / Houston, Sandra (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation describes development of a procedure for obtaining high quality, optical grade sand coupons from frozen sand specimens of Ottawa 20/30 sand for image processing and analysis to quantify soil structure along with a methodology for quantifying the microstructure from the images. A technique for thawing and stabilizing frozen core samples was developed using optical grade Buehler® Epo-Tek® epoxy resin, a modified triaxial cell, a vacuum/reservoir chamber, a desiccator, and a moisture gauge. The uniform epoxy resin impregnation required proper drying of the soil specimen, application of appropriate confining pressure and vacuum levels, and epoxy mixing, de-airing and curing. The resulting stabilized sand specimen was sectioned into 10 mm thick coupons that were planed, ground, and polished with progressively finer diamond abrasive grit levels using the modified Allied HTP Inc. polishing method so that the soil structure could be accurately quantified using images obtained with the use of an optical microscopy technique. Illumination via Bright Field Microscopy was used to capture the images for subsequent image processing and sand microstructure analysis. The quality of resulting images and the validity of the subsequent image morphology analysis hinged largely on employment of a polishing and grinding technique that resulted in a flat, scratch free, reflective coupon surface characterized by minimal microstructure relief and good contrast between the sand particles and the surrounding epoxy resin. Subsequent image processing involved conversion of the color images first to gray scale images and then to binary images with the use of contrast and image adjustments, removal of noise and image artifacts, image filtering, and image segmentation. Mathematical morphology algorithms were used on the resulting binary images to further enhance image quality. The binary images were then used to calculate soil structure parameters that included particle roundness and sphericity, particle orientation variability represented by rose diagrams, statistics on the local void ratio variability as a function of the sample size, and the local void ratio distribution histograms using Oda's method and Voronoi tessellation method, including the skewness, kurtosis, and entropy of a gamma cumulative probability distribution fit to the local void ratio distribution.
ContributorsCzupak, Zbigniew David (Author) / Kavazanjian, Edward (Thesis advisor) / Zapata, Claudia (Committee member) / Houston, Sandra (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
As a prelude to a study on the post-liquefaction properties and structure of soil, an investigation of ground freezing as an undisturbed sampling technique was conducted to investigate the ability of this sampling technique to preserve soil structure and properties. Freezing the ground is widely regarded as an appropriate technique to recover undisturbed samples of saturated cohesionless soil for laboratory testing, despite the fact that water increases in volume when frozen. The explanation generally given for the preservation of soil structure using the freezing technique was that, as long as the freezing front advanced uni-directionally, the expanding pore water is expelled ahead of the freezing front as the front advances. However, a literature review on the transition of water to ice shows that the volume of ice expands approximately nine percent after freezing, bringing into question the hypothesized mechanism and the ability of a frozen and then thawed specimen to retain the properties and structure of the soil in situ. Bench-top models were created by pluviation of sand. The soil in the model was then saturated and subsequently frozen. Freezing was accomplished using a pan filled with alcohol and dry ice placed on the surface of the sand layer to induce a unidirectional freezing front in the sample container. Coring was used to recover frozen samples from model containers. Recovered cores were then placed in a triaxial cell, thawed, and subjected to consolidated undrained loading. The stress-strain-strength behavior of the thawed cores was compared to the behavior of specimens created in a split mold by pluviation and then saturated and sheared without freezing and thawing. The laboratory testing provide insight to the impact of freezing and thawing on the properties of cohesionless soil.
ContributorsKatapa, Kanyembo (Author) / Kavazanjian, Edward (Thesis advisor) / Houston, Sandra (Committee member) / Zapata, Claudia (Committee member) / Arizona State University (Publisher)
Created2011
Description
The infrastructure is built in Unsaturated Soils. However, the geotechnical practitioners insist in designing the structures based on Saturated Soil Mechanics. The design of structures based on unsaturated soil mechanics is desirable because it reduces cost and it is by far a more sustainable approach. The research community has identified the Soil-Water Characteristic Curve as the most important soil property when dealing with unsaturated conditions. This soil property is unpopular among practitioners because the laboratory testing takes an appreciable amount of time. Several authors have attempted predicting the Soil-Water Characteristic Curve; however, most of the published predictions are based on a very limited soil database. The National Resources Conservation Service has a vast database of engineering soil properties with more than 36,000 soils, which includes water content measurements at different levels of suctions. This database was used in this study to validate two existing models that based the Soil-Water Characteristic Curve prediction on statistical analysis. It was found that although the predictions are acceptable for some ranges of suctions; they did not performed that well for others. It was found that the first model validated was accurate for fine-grained soils, while the second model was best for granular soils. For these reasons, two models to estimate the Soil-Water Characteristic Curve are proposed. The first model estimates the fitting parameters of the Fredlund and Xing (1994) function separately and then, the predicted parameters are fitted to the Fredlund and Xing function for an overall estimate of the degree of saturation. Results show an overall improvement on the predicted values when compared to existing models. The second model is based on the relationship between the Soil-Water Characteristic Curve and the Pore-Size Distribution of the soils. The process allows for the prediction of the entire Soil-Water Characteristic Curve function and proved to be a better approximation than that used in the first attempt. Both models constitute important tools in the implementation of unsaturated soil mechanics into engineering practice due to the link of the prediction with simple and well known engineering soil properties.
ContributorsTorres Hernández, Gustavo (Author) / Zapata, Claudia (Thesis advisor) / Houston, Sandra (Committee member) / Witczak, Matthew (Committee member) / Arizona State University (Publisher)
Created2011
Description
The goal of this project was to develop criteria to signify when a soil specimen is just on the verge of failure when tested in a consolidated-drained triaxial test. By identifying the imminent failure of the specimen, a multi-stage triaxial test can be automated, allowing for soil strength properties to be determined from a single specimen. The purpose of identification of imminent failure of the specimen is for purposes of development of automated multi-stage test operation of a single specimen for determination of soil properties. Currently, shear strength parameters for a soil could either be calculated from at least three separate triaxial tests or a multi-stage test where each stage would end based on the operator's judgement. By developing generalized criteria that would signify failure, and therefore the need to move on to the next stage of a multi-state test, a computer program could be used to automatically end one loading stage and begin the next. This automation would allow for a wider use of multi-stage tests, which are faster and therefore less expensive to run than three standard triaxial tests. Triaxial tests were performed on loose and dense sand specimens. During standard testing, the loose sand had a friction angle of 29.61o and the dense sand had a friction angle of 38.63o. Using a zero tangent modulus as the stage-end criteria, the loose sand had a friction angle of 27.69o and the dense sand had a friction angle of 37.03o. Using the maximum volumetric strain as the stage-end criteria, the loose sand had a friction angle of 25.16o. The multi-stage shear strength parameters were reasonable compared to the single-stage test parameters, if slightly conservative. This suggests that computer automation of multi-stage triaxial tests will produce results that can be used in analysis and design by geotechnical engineers. However, more research will be required to confirm this initial assumptions for a wider range of sand gradations as well as for other soil types and testing conditions.
ContributorsPhillips, Zachary Ryan (Author) / Houston, Sandra (Thesis director) / Lawrence, Christopher (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The purpose of this research was to introduce unsaturated soil mechanics to the undergraduate geotechnical engineering course in a concise and easy to understand manner. Also, it was essential to develop unsaturated soil mechanics teaching material that merges smoothly into current undergraduate curriculum and with sufficient flexibility for broad adaptation by faculty. The learning material consists of three lecture modules and a laboratory module. The lecture modules introduced soil mechanics for the general 3-phase medium condition with the saturated soil as a special case. The three lecture modules that were developed are (1) the stress state variables for unsaturated soils, (2) soil-water characteristic curves, and (3) axis translation. A PowerPoint presentation was created to present each module in an easy to understand manner so that the students will enjoy the learning material. Along with the lecture modules, a laboratory module was developed that reinforced the key aspects and concepts for unsaturated soil behavior. A laboratory manual was created for the Tempe Pressure Cell and Fredlund SWC-150 device (one-dimensional oedometer pressure plate device) in order to give the instructor and institution a choice of which testing equipment best fits their program. Along with the laboratory manuals, an analysis guide was created to help students with constructing SWCCs from their laboratory. A soil type recommendation was also researched for use in the laboratory module. The soil ensured acceptably short equilibrium times along with a wide range or suction values controllable by both testing equipment (Tempe Pressure Cell and Fredlund SWC-150). A silt type soil material was recommended for the laboratory module. As a part of this research, a smooth transition from unsaturated to saturated condition was demonstrated through laboratory volume change experiments using a silt soil tested in an oedometer-type pressure plate device. Three different experiments were conducted: (1) volume change for unsaturated soils in response to suction and net normal stress change, (2) volume change for saturated soils in response to effective stress change, as determined using unsaturated soils testing equipment, and (3) traditional consolidation tests on saturated soil using a conventional consolidometer device.
ContributorsRamirez, Eddy F (Author) / Houston, Sandra (Thesis advisor) / Zapata, Claudia (Thesis advisor) / Savenye, Wilhelmina (Committee member) / Arizona State University (Publisher)
Created2013
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