Matching Items (4)
Filtering by
- All Subjects: Geotechnology
- Creators: van Paassen, Leon
Description
Enzyme-induced carbonate precipitation (EICP) is a biogeotechnical soil improvement method that involves the precipitation of calcium carbonate via hydrolysis of urea (ureolysis) catalyzed by free urease enzyme in a calcium chloride solution. When this reaction takes place in the pore space of a sand, the precipitated calcium carbonate may bind soil grains together, thereby improving strength. Three studies on EICP are presented in this dissertation. In the first study, chemical equilibrium modeling via PHREEQC is used to develop a method for evaluating urease activity from electrical conductivity (EC) measurements in a closed reactor containing urea and urease. It is shown that a commonly used correlation to estimate urease activity from EC measurements overestimates the initial urea hydrolysis rate (thereby overpredicting the urease activity as well). In the second study, the crystal structure and mechanical properties of calcium carbonate minerals formed by EICP are studied. It is shown that a “modified” precipitate synthesized by the inclusion of nonfat dry milk in the EICP solution is more ductile than a “baseline” precipitate synthesized from an EICP solution without nonfat milk. Additionally, in sands biocemented using the modified EICP solution, precipitation occurs preferentially at the grain contacts. This may contribute to relatively high unconfined compressive strengths at low carbonate contents in some EICP-treated sands. The third study discusses the role of some sand characteristics on the strength following modified EICP treatment. Three batches of Ottawa 20-30 sand from different sources were treated identically using the modified EICP solution. Subsequent testing showed large differences in their unconfined compressive strengths. It is shown that this variation in unconfined compressive strength is due to differences in the surface microtexture and surface mineralogy of the sands.The fundamental studies presented in this dissertation provide a deeper understanding of some aspects of the EICP process.
ContributorsLakshminarayanan, Vinaykrishnan (Author) / Kavazanjian, Jr., Edward (Thesis advisor) / van Paassen, Leon (Committee member) / Khodadadi Tirkolaei, Hamed (Committee member) / Arizona State University (Publisher)
Created2022
Description
The Atlantic razor clam burrows underground with effectiveness and efficiency by coordinating shape changings of its shell and foot. Inspired by the burrowing strategy of razor clams, this research is dedicated to developing a self-burrowing technology for active underground explorations by investigating the burrowing mechanism of razor clams from the perspective of soil mechanics. In this study, the razor clam was observed to burrow out of sands simply by extending and contracting its foot periodically. This upward burrowing gait is much simpler than its downward burrowing gait, which also involves opening/closing of the shell and dilation of the foot. The upward burrowing gait inspired the design of a self-burrowing-out soft robot, which drives itself out of sands naturally by extension and contraction through pneumatic inflation and deflation. A simplified analytical model was then proposed and explained the upward burrowing behavior of the robot and razor clams as the asymmetric nature of soil resistances applied on both ends due to the intrinsic stress gradient of sand deposits. To burrow downward, additional symmetry-breaking features are needed for the robot to increase the resistance in the upward burrowing direction and to decrease the resistance in the downward burrowing direction. A potential approach is by incorporating friction anisotropy, which was then experimentally demonstrated to affect the upward burrowing of the soft robot. The downward burrowing gait of razor clams provides another inspiration. By exploring the analogies between the downward burrowing gait and in-situ soil characterization methods, a clam-inspired shape-changing penetrator was designed and penetrated dry granular materials both numerically and experimentally. Results demonstrated that the shell opening not only contributes to forming a penetration anchor by compressing the surrounding particles, but also reduces the foot penetration resistance temporally by creating a stress arch above the foot; the shell closing facilitates the downward burrowing by reducing the friction resistance to the subsequent shell retraction. Findings from this research shed lights on the future design of a clam-inspired self-burrowing robot.
ContributorsHuang, Sichuan (Author) / Tao, Junliang (Thesis advisor) / Kavazanjian, Edward (Committee member) / Marvi, Hamidreza (Committee member) / Zapata, Claudia (Committee member) / van Paassen, Leon (Committee member) / Arizona State University (Publisher)
Created2020
Description
Enzyme induced carbonate precipitation (EICP) treatment is a stabilization method of dust mitigation that applies a spray-on treatment to form a soil crust and increase the wind erosion resistance of a disturbed soil surface. The purpose of this work was to evaluate the EICP treatment with multiple field and laboratory test methods for measuring the wind erosion resistance of EICP treated soil. The threshold friction velocity (TFV) is defined as the minimum wind speed required to initiate continuous particle movement and represents the wind erosion resistance of a soil surface. Tested soil type and textures included a clean fine sand to a loamy sandy soil that contained a significant amount of fines. Dry untreated soil and disturbed field soil surfaces were compared to a chloride salt solution treatment and an EICP treatment solution in both laboratory and field testing to evaluate the wind erosion resistance of the treatments.
ContributorsWoolley, Miriam Arna (Author) / Kavazajian, Edward (Thesis advisor) / van Paassen, Leon (Committee member) / Khodadaditirkolaei, Hamed (Committee member) / Hamdan, Nasser (Committee member) / Arizona State University (Publisher)
Created2023
Description
Microbially- and enzyme-induced carbonate precipitation (EICP and MICP) offer potentially sustainable and cost-effective mitigation methods for fugitive dust by forming an erosion-resistant crust on the soil through precipitation of a natural calcium carbonate (CaCO3) cement. While there have been isolated studies on the efficacy of the carbonate precipitation process, there are few systematic studies of the influence of the properties of the soil being treated (e.g., gradation, salt content) on the precipitation and the resulting wind erosion resistance. Moreover, the influence of environmental conditions on the durability of the crust formed by the induced carbonate precipitation has not been systematically investigated. In this research program, the efficacy and durability of EICP and MICP for dust mitigation were investigated for a variety of soil types and in different environmental conditions. Soil samples from seven sites with fugitive dust problems were treated with MICP or EICP and subjected to lab or field testing. The results of these tests showed that the effectiveness of biocementation treatment varies depending on the grain size distribution of soil and mineralogical composition. Testing on iron ore tailings materials demonstrated that treating by application of EICP solutions at lower concentrations (i.e., 0.5M and 0.75M of urea and calcium chloride) yielded effective results for poorly graded fine sand-sized tailings but the same solutions were ineffective for the well graded sand-sized tailings that contained large gravel-sized particles. Additionally, the application of MICP and EICP on sediments adjacent to a shrinking lake (the Salton Sea) with different salt contents exhibited enhanced performance in soils with lower salt content. The effect of temperature during deployment and precipitation cycles are shown to be significant environmental factors by simulating wetting-drying and freeze-thaw cycles in the laboratory. A dust-resistance crust formed through biocementation remained mostly intact after undergoing multiple cycles of wetting-drying. However, the durability of a dust-resistance crust formed through biocementation to multiple cycles of freeze-thaw depended on treatment solution concentration and soil grain size. Additionally, high temperature during field deployment of MICP adversely effected crust formation due to rapid evaporation that inhibited the complete hydrolysis of urea and the precipitation of carbonate.
ContributorsEhsasi, Farideh (Author) / Kavazanjian, Edward (Thesis advisor) / van Paassen, Leon (Committee member) / Khodadaditirkolaei, Hamed (Committee member) / Arizona State University (Publisher)
Created2023