This thesis focuses on large-scale direct simple shear (LDSS) testing to analyze the behavior of coarse mine tailings subject to cyclic loading. The motivation behind this research stems from recent failures of tailings dams, prompting mine owners globally to reassess the safety of their tailing’s impoundments. Testing was carried out at the Arizona State University (ASU) Enamul and Mahmuda Hoque geotechnical laboratory using a unique LDSS device. Cyclic shearing, at different levels of strains, under constant normal stress test was carried out to investigate the modulus reduction and damping behavior of the tailings. Constant volume tests were conducted to simulate the undrained behavior of the tailings and provide insight to the tailings’ liquefaction potential. In both the constant normal stress and constant volume tests the tailings were sheared to the strain limit of the device to assess the post-cyclic shear behavior of the tailings. Testing was also conducted on tailings from the same parent material after screening the larger particle to evaluate the effect of the particle size. The thesis also includes recommendations for improving future test results. This thesis provides valuable insights on the behavior of coarse mine tailings which ultimately contributes to enhancing safety and environmental sustainability in the mining industry.

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.

This Master's thesis presents an experimental testing program conducted to assess the properties of coarse tailings from two Arizona copper mine heap leach pads. This testing program was motivated by recent failures in tailings impoundments, which has prompted a re-evaluation of tailings deposit stability worldwide. The testing was conducted using a unique large-scale Direct-Simple Shear (LDSS) device at Arizona State University (ASU). Prior to testing the tailings, the LDSS device had to be rehabilitated, as it had not been used for several years. The testing program included one-dimensional compression testing, shear wave velocity measurement, and monotonic shearing under constant volume conditions. The test results demonstrate the effectiveness of the LDSS device in obtaining representative data for tailings under monotonic loading. Recommendations for future improvements of the LDSS include enhancing the connection of monitoring instruments, utilizing more sophisticated software for shear wave velocity measurements, and optimizing the control system. The thesis contributes to geotechnical engineering by improving understanding and evaluation of tailings properties, thereby enhancing safety and environmental sustainability in the mining industry.

Some subterranean animals, such as mole-rats, can burrow underground, sense the environment around them, and communicate with each other. Inspired by the mole-rats, this dissertation is dedicated to developing an active wireless underground sensor network (WUSN) for active underground exploration. Special attention is paid to two key functions: wireless underground data transmission, and underground self-burrowing. In this study, a wireless underground communication system based on seismic waves was developed. The system includes a bio-inspired vibrational source, an accelerometer as the receiver, and a set of algorithms for encoding and decoding information. With the current design, a maximum transmission bit rate of 16–17 bits per second and a transmission distance of 80 cm is achieved. The transmission range is limited by the size of container used in the laboratory experiments. The bit error ratio is as low as 0.1%, demonstrating the robustness of the algorithms. The performance of the developed system shows that seismic waves produced by vibration can be used as an information carrier and can potentially be implemented in the active WUSNs. A minimalistic horizontal self-burrowing robot was designed. The robot mainly consists of a tip (flat, cone, or auger), and a pair of cylindrical parts. The robot can achieve extension-contraction with the utilization of a linear actuator and have options for tip rotation with an embedded gear motor. Using a combined numerical simulation and laboratory testing approach, symmetry-breaking is validated to be the key to underground burrowing. The resistance-displacement curves during the extension-contraction cycles of the robot can be used to quantify the overall effect of asymmetries and estimate the burrowing behavior of the robots. Findings from this research shed light on the future development of self-burrowing robots and active WUSNs.

Seed awns (Erodium and Pelargonium) bury themselves into ground for germination usinghygroscopic coiling and uncoilingmovements. Similarly,wormlizards (Amphisbaenia) create tunnels for habitation by oscillating their heads along the long axis of the trunks. Inspired by these burrowing strategies, this research aims to understand these mechanisms from a soil mechanics perspective, investigate the factors influencing penetration resistance, and develop a self-burrowing technology for subterranean explorations. The rotational movements of seed awns, specifically their coiling and uncoiling movements, were initially examined using the Discrete Element Method (DEM) under shallow and dry conditions. The findings suggest that rotation reduces penetration resistance by decreasing penetrator-particle contact number and the force exerted, and by shifting the contact force away from vertical direction. The effects of rotation were illustrated through the force chain network, displacement field, and particle trajectories, supporting the "force chain breakage" hypothesis and challenging the assumptions of previous analytical models. The factors reducing penetration resistance were subsequently examined, both numerically and experimentally. The experimental results link the reduction of horizontal penetration resistance to embedment depth and penetrator geometry. Notably, both numerical and experimental results confirm that the reduction of penetration resistance is determined by the relative slip velocity, not by the absolute values. The reduction initially spikes sharply with the relative slip velocity, then increases at a slower rate, leveling off at higher relative slip velocities. Additional findings revealed a minimal impact of relative density, particle shape, and inertial number on penetration resistance reduction. Conversely, interface friction angle appeared to increase the reduction, while penetrator roundness and confining pressure decreased it. The investigation also extended to the effect of rotational modes on the reduction of penetration resistance. Reductions between cone-continuous rotation (CCR) and cone-oscillatory rotation (COR) cases were i comparable. However, whole-body-continuous rotation (WCR) yielded a higher reduction under the same relative slip velocities. Interestingly, the amplitude of oscillation movement demonstrated a negligible effect on the reduction. Lastly, a self-burrowing soft robot was constructed based on these insights. Preliminary findings indicate that the robot can move horizontally, leveraging a combination of extensioncontraction and rotational movements.

It has been found that certain biological organisms, such as Erodium seeds and Scincus scincus, are capable of effectively and efficiently burying themselves in soil. Biological Organisms employ various locomotion modes, including coiling and uncoiling motions, asymmetric body twisting, and undulating movements that generate motion waves. The coiling-uncoiling motion drives a seed awn to bury itself like a corkscrew, while sandfish skinks use undulatory swimming, which can be thought of as a 2D version of helical motion. Studying burrowing behavior aims to understand how animals navigate underground, whether in their natural burrows or underground habitats, and to implement this knowledge in solving geotechnical penetration problems. Underground horizontal burrowing is challenging due to overcoming the resistance of interaction forces of granular media to move forward. Inspired by the burrowing behavior of seed-awn and sandfish skink, a horizontal self-burrowing robot is developed. The robot is driven by two augers and stabilized by a fin structure. The robot’s burrowing behavior is studied in a laboratory setting. It is found that rotation and propulsive motion along the axis of the auger’s helical shape significantly reduce granular media’s resistance against horizontal penetration by breaking kinematic symmetry or granular media boundary. Additional thrusting and dragging tests were performed to examine the propulsive and resistive forces and unify the observed burrowing behaviors. The tests revealed that the rotation of an auger not only reduces the resistive force and generates a propulsive force, which is influenced by the auger geometry, rotational speed, and direction. As a result, the burrowing behavior of the robot can be predicted using the geometry-rotation-force relations.

Environmentally harmful byproducts from solid waste’s decomposition, including methane (CH4) emissions, are managed through standardized landfill engineering and gas-capture mechanisms. Yet only a limited number of studies have analyzed the development and composition of Bacteria and Archaea involved in CH4 production from landfills. The objectives of this research were to compare microbiomes and bioactivity from CH4-producing communities in contrasting spatial areas of arid landfills and to tests a new technology to biostimulate CH4 production (methanogenesis) from solid waste under dynamic environmental conditions controlled in the laboratory. My hypothesis was that the diversity and abundance of methanogenic Archaea in municipal solid waste (MSW), or its leachate, play an important role on CH4 production partially attributed to the group’s wide hydrogen (H2) consumption capabilities. I tested this hypothesis by conducting complementary field observations and laboratory experiments. I describe niches of methanogenic Archaea in MSW leachate across defined areas within a single landfill, while demonstrating functional H2-dependent activity. To alleviate limited H2 bioavailability encountered in-situ, I present biostimulant feasibility and proof-of-concepts studies through the amendment of zero valent metals (ZVMs). My results demonstrate that older-aged MSW was minimally biostimulated for greater CH4 production relative to a control when exposed to iron (Fe0) or manganese (Mn0), due to highly discernable traits of soluble carbon, nitrogen, and unidentified fluorophores found in water extracts between young and old aged, starting MSW. Acetate and inhibitory H2 partial pressures accumulated in microcosms containing old-aged MSW. In a final experiment, repeated amendments of ZVMs to MSW in a 600 day mesocosm experiment mediated significantly higher CH4 concentrations and yields during the first of three ZVM injections. Fe0 and Mn0 experimental treatments at mesocosm-scale also highlighted accelerated development of seemingly important, but elusive Archaea including Methanobacteriaceae, a methane-producing family that is found in diverse environments. Also, prokaryotic classes including Candidatus Bathyarchaeota, an uncultured group commonly found in carbon-rich ecosystems, and Clostridia; All three taxa I identified as highly predictive in the time-dependent progression of MSW decomposition. Altogether, my experiments demonstrate the importance of H2 bioavailability on CH4 production and the consistent development of Methanobacteriaceae in productive MSW microbiomes.

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.

Two challenges in the implementation of enzyme induced carbonate precipitation(EICP) are the cost of enzyme and the variability of the enzyme. Urease enzyme costs can be lowered drastically with the use of crude extract from plant materials, but experience has shown variability in the source of the crude urease enzyme, the crude urease enzyme extraction methods, and the concentration of the EICP solution can cause significant variability in the efficacy of the EICP solution. This thesis examines the variability in the efficacy of crude enzyme derived from jack beans (Canavalia ensiformis) and sword beans (Canavalia gladiata), two of the most commonly used sources of urease enzyme for EICP. The sources of variability investigated herein include the crude extraction method (including the effect of the bean husks on extraction) and different chemical constituent concentrations. These effects were assessed using enzyme activity measurements and precipitation efficiency tests. The activity tests were performed via spectrophotometry using Nessler's reagent. The precipitation tests looked at the influence of chemical constituent concentrations of 0.67 M calcium chloride and 1 M urea with non-fat dry milk in the EICP solutions and a higher concentration solution with chemical constituent concentrations of 2 M for both calcium chloride and urea with non-fat dry milk. The high concentration solution was selected based on preliminary testing results to maximize carbonate precipitation in one cycle of treatment. Significant sources of a decline in activity (and increase in variation) of the crude urease enzyme were found in extraction from sword beans with husks, high chemical constituent concentrations, and juicing instead of cheesecloth filtration. This thesis also examines the accuracy of commonly used correlation factors for converting electrical conductivity to urease enzyme activity. Crude jack bean and sword bean urease enzyme activity measurement via electrical conductivity was found to have a correlation coefficient that differed from the previously reported correlation when compared to activity measured via the more accurate spectrophotometry using Nessler’s reagent measurements.

The climate-driven volumetric response of unsaturated soils (shrink-swell and frost heave) frequently causes costly distresses in lightly loaded structures (pavements and shallow foundations) due to the sporadic climatic fluctuations and soil heterogeneity which is not captured during the geotechnical design. The complexity associated with the unsaturated soil mechanics combined with the high degree of variability in both the natural characteristics of soil and the empirical models which are commonly implemented tends to lead to engineering judgment outweighing the results of deterministic computations for the basis of design. Recent advances in the application of statistical techniques and Bayesian Inference in geotechnical modeling allows for the inclusion of both parameter and model uncertainty, providing a quantifiable representation of this invaluable engineering judgement. The overall goal achieved in this study was to develop, validate, and implement a new method to evaluate climate-driven volume change of shrink-swell soils using a framework that encompasses predominantly stochastic time-series techniques and mechanistic shrink-swell volume change computations. Four valuable objectives were accomplished during this research study while on the path to complete the overall goal: 1) development of an procedure for automating the selection of the Fourier Series form of the soil suction diffusion equations used to represent the natural seasonal variations in suction at the ground surface, 2) development of an improved framework for deterministic estimation of shrink-swell soil volume change using historical climate data and the Fourier series suction model, 3) development of a Bayesian approach to randomly generate combinations of correlated soil properties for use in stochastic simulations, and 4) development of a procedure to stochastically forecast the climatic parameters required for shrink-swell soil volume change estimations. The models presented can be easily implemented into existing foundation and pavement design procedures or used for forensic evaluations using historical data. For pavement design, the new framework for stochastically forecasting the variability of shrink-swell soil volume change provides significant improvement over the existing empirical models that have been used for more than four decades.