Geo-Congress 2020: Geo-Systems, Sustainability, Geoenvironmental Engineering, and Unsaturated Soil Mechanics

This paper focuses on experimental investigation of the effect of temperature on coupled thermo-hydraulic properties of glacial tills. During operation of a geothermal system, geomaterials are subjected to thermal gradients that may significantly affect the hydraulic properties. An accurate characterization of these properties under representative field conditions is essential to provide input parameters for an efficient design. Therefore, this study focuses on the effect of temperature on hydraulic properties of glacial tills. Core samples at different depths were collected from a borehole for a planned geothermal site on the University of Illinois at Urbana-Champaign campus. A core flooding apparatus was used to perform experiments on saturated samples to characterize hydraulic properties of glacial tills at different temperatures and representative in situ stresses. The results revealed that the intrinsic permeability and hydraulic conductivity significantly increased with increasing temperatures. The increase was more pronounced at lower lateral stresses. An accurate characterization of coupled thermo-hydraulic properties of glacial tills will allow to the development of constitutive relationships for saturated geomaterials.

The design of high-pressure high-temperature pipelines (HPHT pipelines) is mainly governed by pipe-soil interaction considerations. Over the past few years, a number of studies have set as their goal to reliably characterize the soil-pipeline interface behavior. Independent research groups utilized different test setups and methodologies to study this interface behavior, with the tilt table test and the interface direct shear test being the most common testing approaches. To date, there are no published efforts that show direct comparisons between results from these two testing systems. The objectives of this paper are to (1) design and fabricate tilt table and interface direct shear testing setups that are capable of measuring the drained interface resistance between pipelines and clays, (2) use these setups to study the effects of low effective normal stresses and type of pipeline coating on the drained clay-pipe interface response, and (3) compare the results from tilt table and interface direct shear tests under identical interface and soil conditions. The results allow for drawing conclusions on the adequacy of the two testing methodologies in determining interface strength properties that will aid the design of offshore pipelines in soft clays.

Once soil temperature reaches a critical temperature due to heat generated from a heat source (e.g., ground-based heat exchangers, buried electrical cables), moisture migration is initiated, which may result in a significant change in soil thermal conductivity. In this study, laboratory testing was performed to evaluate how initial moisture content affects soil critical temperature. Temperature and moisture contents of three sandy soils at 1% and 3% initial moisture contents were measured using a radial-based apparatus, including a centrally placed heating element. While discontinuities near the boundary between dry and wet zones were clearly observed in soils at 3% initial moisture content, the 1% initial moisture content cases had gradual temperature profiles instead of pronounced discontinuities. Temperature and moisture profiles were thus used with soil images to determine critical temperature. As initial moisture content increased from 1% to 3%, moisture migration decreased with an increase in critical temperature average from 31.6 °C to 44.7 °C. This experimental data supports the concept that soil critical temperature is not a constant for a soil compacted to the same density and that other mechanistic attributes are causative.

This paper presents an analytical model relating the thermally-induced pore water pressures to the volume changes in saturated soils. In fully drained conditions, normally consolidated clays subjected to elevated temperatures undergo thermally-induced volume contractions. On the other hand, the thermally-induced pore water pressure is generated under fully undrained conditions. Fully drained or fully undrained conditions are not practical for in situ conditions as the rates of applied temperature change varies with time. The developed analytical relation was validated against experimental results showing the ability of the model to predict the thermally-induced pore water pressure and volume change versus time.

The mechanical behavior of clays is altered when it is exposed to freezing-thawing cycles. Freezing-thawing results in volume change increasing the clay permeability. While there are numerous macroscale experiments to prove the evolution of the mechanical behavior of clay, limited amount of microscale experiments exist to evaluate the microfabric changes in clay. In this study, six specimens were subjected to temperature changes using a thermo-mechanical triaxial apparatus under single drainage and double drainage boundary conditions to mimic the natural drainage conditions of clay deposits. The specimens were then freeze-dried to preserve their microstructure before and after thermal paths. Moreover, the specific surface area of each specimen was approximated using N₂-gas sorption method and BET (Brunauer-Emmett-Teller) analysis. Finally, macro-scale behavior of frozen-thawed clays was justified by the evolution of microstructure. Experimental results suggest that access to free water has a significant impact on the thermal behavior of clays during freezing and thawing.

This paper introduces two novel methods of using waste materials i.e., steel furnace slag (SFS), coal wash (CW), and rubber crumbs (RC) in rail tracks. One method is to optimize the mixtures of SFS, CW, and RC (SFS+CW+RC matrix) compacted with the standard compaction energy to serve as a subballast material. The other one is to examine the potential usage of CW and RC mixtures (CW+RC matrix) which are compacted under adjusted compaction effort. To investigate the geotechnical properties of these waste mixtures, comprehensive laboratory tests have been conducted. Based on the test results, the stress-strain relationship is studied with special focus on the effect of rubber content on the ductility and energy-absorbing potential of the proposed mixtures. In addition, for the CW+RC matrix, the role of rubber content and compaction effort on the compaction and degradation characteristics of the material is examined.

Underground stormwater storage units molded from polymeric materials are increasingly popular because they can provide a cost-effective alternative to crushed stone, concrete, or pipe chamber stormwater detention and storage solutions. Because these units are buried underground, they are subjected to lateral and vertical loads from the surrounding soil. This paper presents the results of a series of experiments evaluating the strength and stiffness of one proprietary system composed of rugged, lightweight polypropylene panels and PVC structural columns under vertical, lateral, and combined loads. Experimental results are used to estimate the safety factors and deformations associated with in-service conditions and provide design recommendations. The laboratory testing program shows that the most critical mode of failure of the detention unit is the bending of the PVC columns resulting from lateral earth loading, typically a loading condition occurring at the perimeter of the system. Even when such a system is designed within specifications, its safety factor due to column bending is critically low. It was also found that deck compression deformations due to lateral earth pressures will create space between modules, allowing them to rack and can potentially lead to tension cracks in the adjacent soil, especially in longer installations. When the final grade above and adjacent to the installed units is sloping, a slope stability analysis may be necessary.

Shallow geothermal energy systems (SGES) are becoming more common due to their ability to assist in efficient heating and cooling of buildings. These heat exchanger systems can also be integrated within building foundations, thus creating energy geostructures, which do not require the additional installation costs of a borehole field. Despite the popularity of SGES, several challenges remain. One challenge is subjecting SGES to unbalanced heating and cooling loads during the year. If more energy is required for either heating or cooling, the in situ ground temperature could potentially change over time, thus negatively affecting the efficiency of the system. This is especially challenging in heating or cooling dominated climates such as Chicago, Miami, or Houston, and when energy demand profiles are such that they only require energy for heating, such as bridge deck deicing or grain drying. Furthermore, energy foundations cannot be optimized with respect to geometry for heat exchange with the ground as the design is primarily governed by geotechnical design. This paper explores selective utilization of energy piles within a typical energy pile grid to minimize the amount of energy lost in the ground. The study utilizes a calibrated numerical model to investigate different combinations of heat injection and extraction alternatives. The findings from the analyses are evaluated to establish a practical solution to the problem that would not require an advanced control system or significant oversight from a system operator.

Little attention has been paid to the environmental impacts of site characterization even though it is a necessary part of every geotechnical project. A life cycle assessment (LCA) was performed to evaluate the impacts of two commonly implemented site characterization methods: cone penetration testing (CPT) and mud rotary drilling. For each testing type, indicators of total energy consumption, climate change, acidification, eutrophication, respiratory inorganics, and smog formation were evaluated. The potential impacts were computed to provide normalized results for mobilization (per mile traveled), testing operations (per meter borehole depth), sampling (per hour sampling), and borehole sealing (per meter borehole depth). The life cycle impacts of site characterization are also exemplified through scenario modeling of three different testing programs (i.e., a single sounding, a single sounding with sampling, and an industry-representative site investigation program for a medium sized project). Furthermore, the results obtained provide a baseline for comparison against other site investigation methods, including sonic drilling, hollow stem auger drilling, and others.

This study was performed to show the effects of incorporating different percentages of recycled crushed shingles into the local soil found in Memphis, TN, and the surrounding area. Fiberglass-based asphalt shingles are the most common roofing material used for residential roofing in the United States. Over time, roof shingles begin to deteriorate due to weathering and are typically disposed of in landfills. The time for a shingle to completely decompose is typically longer than 300 years. In an effort to be more environmentally conscientious and remediate material waste, shingles have been recycled and used in a variety of roadway and parking lot paving projects. In this study, compaction and permeability tests are performed on loess, the primary soil found in the Memphis area. To gain insight on the use of recycled crushed shingles as a fill material, different percentages of recycled crushed shingles are mixed with the local loess to form a basis of comparison. Results are presented that show the effect of different amounts of recycled crushed shingles on the maximum dry unit weight and coefficient of permeability of Memphis loess.

Compressed air energy storage (CAES) technology has been reemerging as one of viable energy storage options to address challenges coming from the intermittency of renewable energy sources, such as solar and wind energy. CAES is believed to have several distinct merits, including low cost, long lifespan, being environmentally benign, and the flexibility of scale and location. The novel concept of pipe-pile-based micro-scale CAES (PPMS-CAES) was proposed by the authors in which the pipe-pile foundations of a building are actively used as air storage vessels as well as load-bearing elements. But to date, the study of the PPMS-CAES has been limited to analytical and numerical research. In this work, the PPMS-CAES idea is examined further by using a model pile that is scaled down from the actual size of a closed-ended pipe pile for a building foundation. During the experiment, the model pile, embedded in a soil chamber, is subjected to a repeated cycle of compressed air charge-discharge for an extended period. Additionally, the test pile with and without a structural load is monitored to investigate its behavior under the different boundary condition. In particular, strain, temperature, and displacement of the test pile are closely monitored during the air pressurization-depressurization cycles. It is confirmed that the repeated operation of compressed air storage does not compromise the mechanical integrity of the pile. The vertical displacement at the pile head is likely to be accumulated during the extended cycle of air storage and discharge, but the rate of displacement gradually decreases during the cycle. And, the presence of a structural load makes a difference in the magnitude of the accumulated vertical displacement. Furthermore, thermodynamic and energy analysis are conducted with the actual measurement data. The analysis shows that the actual operation is close to the isothermal process and demonstrates that the anticipated storage efficiency is very competitive with the tolerable temperature fluctuation during the air storage and discharge. Finally, the energy analysis calculated that the proposed PPMS-CAES concept can be applied to an actual condo, and potentially various other types of residential buildings.

Coal gangue is the largest residues produced during the mineral processing phase of coal mining. Owing to their ever-increasing production, coal gangue utilization is a matter of great concern due to the carbon emissions and costs associated with its disposal. Therefore, its utilization in geotechnical engineering applications allows bulk consumption. However, understanding the leaching behavior of trace elements prior to its application is essentially. Accordingly, in the present study, the leaching characteristics of coal gangue were analyzed with varying the sizes of the specimen. The coal gangue was pulverised and the fraction passing 0.425 mm, 1 mm, and 4.75 mm sieve sizes was considered for the study. The toxicity characteristic leaching procedure (TCLP) has been adopted for studying the leaching phenomenon of selected trace elements like As, Cu, Se, and Ni. The study has revealed that the rate of leaching of these elements was observed to vary with size of the specimen and higher amount of leaching was noticed for smaller size specimen (0.425 mm). The decrease in pH of the extracted leachate for smaller size fraction enables the amenable mobilisation of trace elements. Further, the increase in interaction time also contributed for greater mobilisation.

In recent times, fly ash and scrap tires are being utilized extensively in geotechnical applications as a fill material due to their favourable properties. Many studies are reported indicating the suitability of soil-tire waste mixtures as geomaterials. In the present study, the viability of using a mixture of granular rubber and fly ash is explored. Granulated rubber of nominal size equal to 9.5 mm, and fly ashes collected from different thermal power plant sources in India are used in the study. Granulated rubber is mixed with fly ash particles in different proportions, i.e., 0%, 9%, 23%, and 37%, and 100% (granulated rubber with respect to the total weight of the mixture). The optimum mix of granulated rubber and fly ash is proposed based on the minimum void ratio obtained on compacted mixtures. The optimum content of granulated rubber is found to be in the range of 35–65% of the mixture (by weight). The shear strength of fly ash-granulated rubber mixtures is tested in large-size direct shear apparatus (size equal to 300 mm x 300 mm x 200 mm; in length, in width, and in width). The shear strength of the mixture is found to increase with the increase in percentage of granulated rubber. In the present study, the variation in the shear strength of mixtures in relation with the volumetric strain response of the mixtures is discussed. The transition of volumetric response from dilative to contractive is observed for the range of granulated rubber-fly ash mixtures tested and is discussed based on granular void ratio.

In this study, the particle breakage and fines generation of due to compaction were investigated for recycled concrete aggregates (RCA). RCA samples containing two common aggregate types, i.e., sedimentary versus igneous, were selected and compacted with a modified Proctor compaction procedure. Sieve analyses pre- and post-compaction showed that both types of RCA were more susceptible to particle breakage when compared to virgin dolomite aggregates. In particular, the sedimentary RCA sample containing dolomite aggregates exhibited significant levels of breakage and fines generation. Degradation of such RCA materials due to compaction may lead to reduced drainage performance and heightened clogging potential, and therefore should be evaluated before they are used as fill materials.

The Americans with Disabilities Act (ADA) includes specific accessibility guidelines. In the case of unpaved trails however, the requirements are less defined; an ADA accessible trail surface must be firm, stable, and slip-resistant. If an unpaved surface could be improved with the use of an additive, more trails can be ADA accessible. A study has been conducted using a naturally occurring pozzolan from the eruption of Mt. Mazama as a binder applied topically to gravel surfaces. Tests included innovative pour tests to determine depth of penetration of binder in various gradations of aggregate and included a comprehensive study of the unconfined compressive strength of mortar cubes created with Portland cement, lime, volcanic ash, and oyster shells. Bench scale trails were also created in the laboratory to determine the firmness and stability of trail surfaces. In addition to the naturally occurring pozzolans, varying percentages of Portland cement, lime, and crushed oyster shells were used as binding materials. Results indicate that Portland cement must be used in conjunction with naturally occurring pozzolans to create a firm and stable surface. Firmness and stability are measurements provided by the beneficial designs rotational penetrometer that convey how prone a surface is to indentation or material removal due to twisting, downward loads. Through application of a cementitious mix including Portland cement and Mt. Mazama volcanic ash, a surface’s firmness and stability can be improved to within acceptable standards.

Alternate wetting and drying of soils arise as a result of seasonal moisture fluctuations which in turn lead to the volume change in soils. An increase in volume caused by an intake of water is termed as swelling, and a reduction in volume occurring due to loss of water is defined as shrinkage. Shrinkage poses a much more serious problem than the swelling and depends on many factors including the sand content. This paper mainly focuses on understanding the role of sand fraction on the swell-shrink pattern of expansive soil. To achieve this objective, the laboratory swell-shrink tests were conducted on both expansive soil (C100) and expansive soil mixed with 50% sand (C50-S50). Digital camera image analyses were performed for identification of cracks during drying cycles. The experimental results show that the vertical, lateral, and volumetric deformations decreased for C50-S50 specimen during each wet-dry (W-D) cycle with reference to the C100 specimen. This is attributed to the reduction in the amount of clay, swelling of clay particles in the inter-void spaces between clay and sand, and encapsulation offered by the sand particles. For C50-S50 specimen, mostly surface cracks were observed and the volume of cracks formed were much lesser compared to C100 specimen.

Municipal solid waste (MSW) landfills are the third largest anthropogenic source of methane (CH₄) emissions in the United States. Part of the CH₄ generated in landfills is converted to carbon dioxide (CO₂) by CH₄-oxidizing bacteria (MOB) present in the landfill cover soil, whose activity is controlled by various environmental factors including temperature. As landfill temperature fluctuates substantially due to seasonal variations and series of reactions during waste decomposition, which may affect the microbial activity and thus, the rates of CH₄ oxidation. This study aims at analyzing the effect of temperature on CH₄ oxidation potential and microbial community structure of methanotrophs in laboratory-based microcosm studies on landfill cover soil. Landfill cover soil samples were incubated at selectively two temperatures 23°C and 50°C, and rates of CH₄ oxidation were measured, and microbial community structure was analyzed using shotgun metagenome sequencing. CH₄ oxidation occurred at both temperatures in soil microcosm tests with highest activity at 23°C. A corresponding shift in the soil microbiota was observed, with a transition from mesophilic to thermophilic methanotrophs with increased incubation temperature. The study shows that temperature is a critical factor affecting rates of CH₄ oxidation in landfill cover soil, and the changing rates of CH₄ oxidation are in part driven by shift in the methylotroph community.

Taconite tailings are the by-product ore-bearing rocks of iron mining, predominantly consisting of silicate and fine magnetite crystals. In recent years, the use of taconite tailings in pavement construction has increased considerably due to their superior mechanical properties. However, an environmental impact assessment of taconite tailings is required before their potential use in construction purposes. Taconite tailings may leach heavy and toxic metals, which could contaminate the soil, surface, and groundwater. Coarse, sand, fine, and composite sized taconite tailings were subjected to pH-dependent leaching tests in the pH range of 2 to 13 to investigate the leaching behavior of aluminum (Al), chromium (Cr), magnesium (Mg), and sulfate (SO₄). In addition, toxic characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), water leach test (WLT), and U.S. Geological Survey (USGS) leach tests were performed to evaluate the leaching behavior of taconite tailings in different environmental conditions. The test results showed the highest concentrations of metals were leached from fine sized taconite, whereas the lowest amounts of metal leached from composite taconite tailings. Al and Cr demonstrated amphoteric leaching patterns, whereas Mg showed a cationic leaching pattern. The leached concentrations of SO₄ were found to be pH-independent at the pH range of 4 to 13. Except for Al, the leached concentrations of other elements were below the U.S. EPA specified maximum contaminant levels (MCLs) for drinking water. Taconite tailings leached the highest metal concentrations in TCLP effluent; therefore, it is recommended as the most conservative test procedure to evaluate the leaching of these metals from taconite tailings.

In this study, an intensive field-testing program was conducted to quantify non-methane volatile organic compound (NMVOC) emissions from five municipal solid waste (MSW) landfills in California. Field measurements in this study were conducted during the dry season. Flux measurements for 64 NMVOC species across different cover systems at the landfills were obtained using the static flux chamber method. Negative (net uptake) and positive (net emissions) NMVOC fluxes ranging from -6.54×10⁻⁴ to 1.81×10⁰ g/m²-day were measured across all landfills. NMVOC surface fluxes decreased from daily to intermediate to final cover systems for the majority of the sites investigated. Quantified surface fluxes were greatest for the alcohol, aldehyde/alkyne, monoterpene, alkane, and ketone NMVOC chemical families. Scaled-up NMVOC emissions for the sites ranged from 0.024 to 2.22 Mg/year, which were lower than scaled-up methane emissions (0.035 to 1,002 Mg/year). For NMVOCs, the highest emissions were measured at the landfill with the highest and lowest percentages of daily and final covers, respectively.

The impact of benzene leakage on underlying unsaturated zone and nearby subsurface drainage concrete pipe is investigated. Work in the paper considers mass transfer into subsurface concrete pipe located in unsaturated profile. The 3D numerical simulations were implemented using the T2VOC code with the Petrasim2018 graphical user interface to analyze multiphase migration in the vadose zone and the impact on the concrete pipeline installed in a trench. The contaminant’s gas, aqueous, and free product phases are assessed based on the model physical properties of soil and concrete materials. A case study is presented with data from a site located in the coastal plain physiographic region of North Carolina (NC). The site is a gas station located near the town of Jacksonville, NC. The analyses consider the effect of depth to groundwater table and volatilization into the atmosphere. The results illustrate the transport of the three phases in unsaturated soil domain and the potential of having the gas and aqueous phases breakthrough the subsurface concrete pipe.

Type and concentration of pore fluids, nature, and quantity of clay minerals, play a major role in inducing alterations in the clayey soil. Moreover, alkali type and its concentration on mineral dissolution and neogenic formations are scanty for specified conditions (temperature, volume of reacting solution, and duration of interaction). In the present study, to clearly perceive the significant impact of alkalis (NaOH/KOH) with varying concentration (0.1–8 N) on dissolution of existing mineral and evolution of new minerals under specified conditions, micro level investigations have been carried out on kaolin. The samples were investigated to bring out the changes in specific surface area (SSA) and cation exchange capacity (CEC). The detailed analysis of the results has corroborated that, original mineral dissolution and neogenic formations largely depend on alkali concentration and its type at a given hydrothermal condition for a particular volume of solution and duration of interaction. Furthermore, at higher concentration of the interacting solutions, complete dissolution of kaolinite mineral is observed. Variations observed in SSA and CEC values of the samples due to NaOH/KOH interactions are well supported by micro level changes.

Landfill gas (LFG) is not only the third largest source of methane gas in the U.S., but also includes hazardous and strongly odorous gas that is often a nuisance to landfill neighbors, resulting in strained relationships with the community, regulatory actions, and, in some cases, costly litigation. As one of the alternatives controlling LFG during the operation of a landfill, a co-extruded geomembrane (GM) with an ethylene vinyl-alcohol (EVOH) layer sandwiched between two inner low-density polyethylene (LLDPE) layers have been introduced to reduce the flux of organic contaminants in the barrier systems of a landfill. In this study, field emissions of methane among LFGs from composite intermediate cover consisting of soils with conventional LLDPE or co-extruded EVOH GM were comparatively evaluated. The field pilot testing site in an operating landfill located in Nebraska was designed and constructed based on minimizing the boundary effect of the cover. The results show significant reduction of methane transport through the EVOH cover. To compare the emission through LLDPE, intermediate cover with EVOH GM reduces the release of gas into the chamber by approximately 85, 73, and 65% after three weeks, two months, and three months, respectively.

During diamond grinding operations for smoothing concrete pavement surfaces, water is used to cool the diamond blades. This water, combined with cutting residue, generates a high pH and high alkaline slurry byproduct referred to as concrete grinding residue (CGR). Although spreading CGR along roadsides is one of the most commonly used disposal methods, it is always of concern because of its potential effect on roadside soil properties. A field study was therefore conducted in 2016 on two roadside slopes beside Highway I-90 in Minnesota on which CGR slurries were offloaded in 2009 and 2013, respectively. The chemical properties of soils that received this CGR were measured and compared with those of adjacent soils that had not received CGR. The areas after receiving CGR slurry exhibited that pH reduced by 0.78 while electrical conductivity (EC) and calcium concentration increased by 0.48 ds m^-1 and 97 mg kg^-1, respectively. Because spreading of CGR did not cause any perceptible reduction in soil quality, CGR was not deemed to be of long-term concern with respect to roadside environments.

This paper aims at studying the influence of acid and alkali solutions on the swell behavior of a non-expansive soil. Sulphuric acid (acidic medium); sodium hydroxide (alkaline medium) of 1 N and 4 N concentrations were used as pore fluids to understand the influence of acid and alkali pore fluids on the swell behavior of kaolin clay relying on one-dimensional free swell tests. Results showed that kaolin clay exhibits maximum equilibrium swelling of about 41% in acidic medium and 22% when interacted with alkaline medium. It is further observed that the magnitude of induced swell in clays is dependent on dispersion of clay particles leading to the formation of new minerals under both acidic and alkaline media. In order to better understand the mechanism responsible, the contaminated soil was investigated for changes in mineralogy and microstructure relying on x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) at the end of interaction. The formation of zeolite minerals viz. sodalite in alkaline media and aluminum sulphate hydrate hydroxide in acidic media were noted from XRD results. Furthermore, SEM studies revealed rosette-type morphological structure(s) in case of 4N NaOH and needle-like structures in H₂SO₄.

Disposal of the increasing amounts of fly ash from coal-fired thermal power plants is a serious concern to the geo-environmentalists. The generated fly ash being disposed in ash ponds acts as source for heavy metal, which leads to soil and water contamination in the vicinity of power plants. In the present study, an attempt was made to measure heavy metal contamination of soil samples, surface water, and ground water around the Kakatiya Thermal Power Plant, Warangal. Soil samples from two locations and water samples from different water sources in the vicinity of thermal plant were analyzed for heavy metal contamination using microwave plasma-atomic emission spectroscopy. Results highlighted that the presence of heavy metal contamination in water samples found to be more than the permissible limits whereas in soil samples, no traces of heavy metals were found. The water drawn from selected sites was largely contaminated by lead (Pb) and mercury (Hg), whose permissible limits were above the WHO and BIS drinking water standards. It was also noted that high concentration of Pb was witnessed. Furthermore, adsorption studies were carried out to lower the concentration of observed metal ions within the drinking water standards. Biochar, a cost-effective material derived from agricultural waste, is used as an adsorbent in this study. Adsorption studies highlighted that the concentration of Pb was successfully brought within the drinking water standards whereas biochar was ineffective with Hg.

Disposal of high-water content sludge wastes can pose problems in landfill operations due to trafficability of compaction equipment, long-term slope stability, and generation of odors. As sludge wastes become increasingly solidified with binding agents, such as cements and fly ashes to improve strength characteristics, the corresponding hydration process of calcium oxide generates heat. The study presents the use bench-scale semi-adiabatic tests to estimate the time required for the heat to dissipate from solidified sludge waste stockpiles. Calorimeters used in hydration testing were made from Dewar flasks which greatly minimizes heat loss to the environment. Heat loss to the environment was estimated using resistor wires. Semi-adiabatic test results are converted to adiabatic time temperature curves using the heat loss estimated from the calorimeter. Materials used in the study include various industrial sludge wastes and ashes. Heat generation of ash and waste mixtures at various ash to waste ratios were performed. A numerical model was developed to estimate the period of heat loss in waste stockpiles so it can be safely landfilled. Climate data was incorporated as boundary conditions in the numerical model.

This study evaluates the comparative unconfined compressive strength (UCS) of compacted lateritic soil improved with Sporosarcina pasteurii (S. pasteurii)-induced calcite precipitate. The soil was treated with varying S. pasteurii suspension densities of 0, 1.50×10⁸, 6.0×10⁸, 1.20×10⁹, 1.80×10⁹, and 2.40×10⁹ cells/ml. Samples were prepared at -2% and +4% moulding water contents relative to optimum (OMC) before compaction using British standard light, BSL (or standard proctor) and west African standard, WAS (or Intermediate) energies, respectively. Results obtained show that higher UCS values were recorded for specimens prepared at -2% relative to OMC regardless of the S. pasteurii suspension density considered. The lower BSL compactive effort gave higher strength values. Peak UCS values of 2,232 kN/m² and 1,808 kN/m² were recorded for specimens treated with S. pasteurii suspension density of 1.20×10⁹ cells/ml when compacted with BSL and WAS energies, respectively. The results from this study has also demonstrated that treatment of compacted lateritic soil with varying S. pasteurii suspension densities prepared at water content of between -2% to +4 % relative to optimum resulted in improvement of the strength characteristics of the soil.

In situ assessment of waste settlements is a critical consideration for the operation, closure, and post-closure development of municipal solid waste (MSW) landfills. Settlement evolution is influenced by the biodegradation processes underway in the waste mass. Presently, the measurement of such settlements involves instrumentation at specific locations on a landfill, or aerial surveys that are generally expensive and not conducted often. An alternative approach is presented herein that involves the use of unmanned aerial vehicles (UAVs) to collect overlapping imagery and create 3D models of landfills using the structure-from-motion technique. Repeated surveys allow for differencing between 3D models to calculate settlement and compute secondary compression indices that can be used in subsequent landfill development. Main advantages of the technique include the generation of cm-level data resolution, the scalability of the approach that allows assessments throughout the entire landfill, and the ability to execute repeated flights for continuous, inexpensive monitoring of spatially resolved settlement. This approach was tested at an MSW landfill in Midland, Michigan, from May 2018 to April 2019, where spatial profiles of the modified secondary compression index were successfully derived from UAV aerial imagery.

Effective recycling and reuse of waste tires can play an important role in addressing environmental and health issues with scrap tire landfills. In New Zealand, gravel-rubber mixtures have been considered as seismic-isolation foundation systems for medium-density low-rise buildings. In this context, this paper, unlike previous studies where sand-rubber mixtures were investigated, gravelly soil is mixed with rubber crumbs with various volumetric proportions of 10%, 25%, and 40%. These gravel-rubber mixtures were tested using a medium-size direct shear apparatus under three vertical stress levels: 30 and 60 kPa, and 100 kPa. The effect of rubber crumbs content on the peak shear strength, friction angle, and dilatancy behaviour of gravelly soil is studied. The results indicate a decrease in shear strength and increase in vertical strain corresponding to peak shear stress with increasing rubber content. A significant reduction in dilatancy was also observed with increasing proportion of rubber crumbs in the mixtures.

A relatively new solution to reduce nitrate export from agricultural drainage is to use existing riparian buffer zones along the field edge as media to provide storage volume by distributing drainage water to saturate the soil, commonly referred to as a “saturated riparian buffer” (SRB). Though previous research has proven the effectiveness of SRBs to reduce nitrate export, uncertainties about long-term impacts prevent widespread adoption of the practice. One significant uncertainty is the stability of the streambank after saturation, raising concerns about slope instability and erosion. Current design standards use conservative guidelines for minimum buffer width and maximum bank height to prevent bank failure from occurring, thereby limiting site eligibility for installation of SRBs. This study investigated the impact of SRB design parameters on the stability of the streambank at a site in Hamilton County, Iowa. Installation of the SRB did not substantially decrease the factor of safety against failure. Additionally, our model shows that a moderate reduction in buffer width decreases the factor of safety but does not lead to slope failure.

BTEX is one of the hazardous organic contaminants available in produced water. Since it has high toxicity, and causes numerous environmental problems, it should be removed up to a limit complying with environmental standards. The objective of this study is to analyze the feasibility of BTEX removal, as the oil pollution index, from produced water by using organoclay as the adsorbent of oil contaminants compared to typical clay. To produce organoclay, CTAB surfactant was used and tested with different cation capacities. The obtained results reveal that organoclay, due to its microstructures, high effectiveness, simplicity, and low cost, is a viable solution to expensive and complicated systems for BTEX removal. Furthermore, organoclay is capable of adsorbing 95.6% BTEX from produced water in the order of ethylbenzene, xylene, toluene, and benzene, respectively.

This work is part of a multi-disciplinary project investigating the use of alternative media for biofiltration systems in Minnesota. Over the last thirty years, the Minnesota Department of Transportation (MnDOT) has implemented biofilters along roadways as a stormwater control measure. These systems must be able to infiltrate and treat the first inch of rainfall onsite to meet state and national regulations. The performance of a biofilter is largely based on its media’s ability to infiltrate water, sustain vegetation, and capture pollutants. To date, MnDOT has relied on sand and compost mixtures for biofilter media amendments. An early phase of this work identified peat as having similar performance characteristics as compost, making it an ideal alternative. A laboratory testing program was also developed during the early phase of work to determine media properties that could be used to predict biofilter performance. Current work focused on characterizing existing biofilters using in situ testing and comparing results to laboratory testing. The comparison of the two methods has enabled an analysis of the predictive capabilities of the laboratory regime. This work also included the instrumentation and monitoring of field sites including a newly constructed peat amended biofilter. Findings from this work have validated the use of peat as a biofilter amendment and shown the developed laboratory testing regime to be a good indicator of field performance. The characterization regime developed through this project and instrumentation methods will be used in the future to identify other beneficial alternative biofilter medias.

Alternative final covers have been increasingly permitted due to the financial benefits and environmental sustainability offered by the use of native soils. However, often due to lack of validated transpiration models, practitioners ignore plants (or transpiration) when equivalency analysis is carried out for permitting. This study focused on evaluating the effect of plants on evapotranspiration (ET) and on the water balance of a 91-cm-thick earthen cover. Two 11 m×11 m (35 ft×35 ft) test sections were built side by side (one planted by Vetiver grass, the other was bare representing control). One-year field data showed that there was no significant difference between overall water balance and ET of the two test sections. The Vetiver plants reached 50% of their specified matured height at end of the first year.

Seismic compression is defined as the accrual of contractive volumetric strains in soils when subjected to earthquake shaking and has been recognized as a crucial cause of seismically induced damage to geotechnical structures. In earthquake-prone areas, seismic compression of unsaturated backfill soils is critical to predict as small settlements may have significant impacts on the performance of overlying infrastructure like bridge decks, roadways, or railways. Accordingly, the goal of this paper is to describe the results from a series of fully undrained cyclic simple shear tests on unsaturated sand specimens subjected to an intermediate shear strain of 1% with separate measurements of pore air and pore water pressures. Sand specimens having a similar initial relative density representative of the backfill used in a recent set of mechanically-stabilized earth (MSE) bridge abutment shaking table experiments were tested, with the initial degrees of saturation and matric suctions in the funicular regime controlled using the hanging column approach. Test results showed a nonlinear relation between the volumetric strains and the degrees of saturation, with the maximum value for an intermediate degree of saturation around 0.3. This was found to be due to the reduction in mean effective stress during cyclic shearing.

This paper presents an elastoplastic solution for undrained expansion of a cylindrical cavity in unsaturated soils. The classical Barcelona basic model has been used to model the mechanical behaviour of the unsaturated soil. The hydraulic behaviour of the soil during cavity expansion coupling with the mechanical behaviour is modeled through a void ratio dependent soil-water characteristic curve. With aid of an auxiliary variable, the problem is finally formulated as a system of first-order ordinary differential equations, and solved as an initial value problem. A parametric study is performed to investigate the effects of suction on the distributions of the stress variables and the expansion responses at the cavity wall during cavity expansion. The results show that the suction has significant effects on the expansion responses of the soil around the cavity. The proposed solution is expected to be able to better interpret the corresponding pressuremeter test data and pile installation effects in unsaturated soils.

Railroad ballasts are poorly graded aggregates that transfer the dynamic weight of railcars from the ties to the subgrade. The ballast section allows for rapid drainage of water through and around the track structure. Fouling is the filling of ballast voids with particles finer than 9.52 mm. Fouling is caused by natural breakdown of ballast during normal track operations, as well as pumping of subgrade from below and capture of falling/flowing materials from above. There is a need for improving the fundamental understanding of ballast degradation characteristics so fouled ballast can be identified in the field more rapidly and reliably. Ballast fouling compromises railway integrity by impeding drainage, and altering the ballast strength. These losses can lead to ballast failure and, ultimately, train derailment. Current state of practice methods for identifying fouled ballast are time intensive, destructive testing methods (e.g., excavation and sieve analysis). Recent advances have been made in nondestructive techniques for ballast fouling detection; however, many of these methods remain unreliable. Fouled ballast is an unsaturated geomaterial; therefore, the objective of this paper is to provide valuable insight into the key relationships between suction and fouling material. Soil water characteristic curves (SWCCs) were measured for five samples of ballast fouling materials using the transient water release and imbibition method. The results indicate that SWCCs from breakdown of ballast were similar to sandy soils and likely did not differ greatly from clean ballast. SWCCs from infiltration of fine grained soil increased the air entry as the percent of fines increased. The SWCC of ballast fouled with coal dust had high air entry and hydraulic conductivity, with lower percent of fines, which was unexpected. These samples present the worst-case scenario of ballast water retention. The long-term goal of this research is to establish the suction and strength characteristics of fouled ballast (including the ballast aggregate) in correlation to ballast fouling and moisture content to improve the assessment of ballast with non-destructive methods, such as ground penetrating radar.

Soil cover systems such as capillary barriers and compacted covers experience cyclic drying and wetting induced by evaporation and infiltration. These wetting and drying cycles have hysteretic effect on hydraulic properties of unsaturated soils. Numerous studies on hysteresis in soil water characteristic curve (SWCC) have been reported in the literature but only a limited number of studies deal with hysteretic unsaturated permeability of compacted sand-clay mixtures. In the present study, a series of laboratory permeability tests have been carried out to investigate the effect of fines on hysteretic hydraulic conductivity of unsaturated soil. The coefficient of unsaturated hydraulic conductivity of sand-kaolin mixtures containing 0%, 10%, and 30% kaolin by dry weight was determined for both drying and wetting cycles. A modified triaxial apparatus was used to apply suction and hydraulic head to measure the unsaturated permeability at different values of matric suction. Test results show that the hysteresis effect on permeability increases considerably with an increase in fines content in sand-clay mixtures.

Temperature variations in low permeable soil (e.g. clay) induce pore pressure, which is known as thermal pressurization. Previous research showed that thermal pressurization highly depends on thermal pressurization coefficient. This coefficient depends on the soil type and changes with temperature due to temperature dependency of thermal expansion coefficient of water. Thermal pressurization is often investigated through thermo-hydro-mechanical (THM) numerical modeling. THM process, with respect to thermal loading, has been examined in the literature to justify the field observations by incorporating advanced thermo-mechanical constitutive models. However, result of numerical simulations using advanced thermo-elastoplastic models still show some discrepancies with experimental and field observations. In this study, the assessment of thermal pressurization in Boom clay is scrutinized through employing a relatively simple while practical thermo-poroelastic finite element model with careful consideration of the temperature-dependent thermal, hydraulic, and mechanical properties of the medium and saturating fluid (i.e. water). The numerical model is carried out using COMSOL Multiphysics and the results of the numerical simulations are compared and validated with the ATLAS project, a large-scale experimental facility in Belgium. The results confirm that thermal and hydraulic coupling parameters are the key factors to change thermal pressurization.

Heat and mass transfers in unsaturated porous media have not been thoroughly investigated in previous studies as most of them assumed that conduction is the only heat transfer mechanism in soil, neglecting convection and phase change while considering constant soil thermal properties. Thermal gradient from a heat source reduces moisture content of the surrounding soil. The dry-out process along with coupled heat and mass transfer can directly affect thermo-hydro-mechanical behavior of soil which has not been previously investigated in the literature. The aim of this study is to evaluate the effect of coupled heat and mass transfer in unsaturated soil and assess the moisture content variation in proximity of a heat source. Hence, a non-equilibrium multiphase flow model is adopted to numerically simulate heat and mass transfer. Different scenarios are defined by changing initial moisture content and heat flux. Results show significant dependency of soil moisture variation to initial conditions.

Key engineering properties of unsaturated soils such as volume change and shear strength can be defined using the effective stress principle. Several problems like prolonged drought, high-level radioactive waste, buried high voltage cables can subject surface and near-surface unsaturated soils to elevated temperatures. Such elevated temperatures can affect the hydraulic and mechanical behavior of unsaturated soils. It is very important to develop a closed-form model that can reasonably estimate the effective stresses under different elevated temperatures. For this purpose, the current study incorporates the temperature effect into a suction stress-based representation of Bishop’s effective stress. The proposed model accounts for the effect of temperature on matric suction and degree of saturation. A temperature-dependent soil water retention curve is used to account for thermal effects on surface tension, contact angle, and enthalpy of immersion per unit area. The proposed effective stress model is then used to calculate the effective stress for two soils, Pachapa loam, and Seochang sandy clay, at various temperatures ranging from 25°C to 100°C. The validity of the model is examined by comparing the predicted effective degree of saturation and suction stress values against the experimental data reported in the literature for GMZ01 bentonite. At a constant net normal stress, the results for both soils show that the impact of temperature on effective stress can be significant. The proposed model can be used for studying geotechnical and geoenvironmental engineering applications that involve elevated temperatures.

Lateral swelling pressure (LSP) develops in silty or clayey soil when the volume expansion of soil is constrained in the horizontal direction. Determination of LSP is important in designing geotechnical structures in expansive soils. Existing methods for derivation of LSP requires several empirical parameters, which are hard to obtain. Furthermore, the majority of the existing models determine LSP assuming the soil is fully saturated which may lead to an over conservative design. Considering the aforementioned limitations, this paper presents an analytical solution for determination of LSP in unsaturated soils. The proposed method attributes the soil expansion to changes in suction stress during infiltration and uses the effective stress-strain relationship to quantify LSP. The proposed model only needs a limited number of soil properties such as the soil water retention curve (SWRC) and Poisson’s ratio along with initial and final soil water contents. The method is compared against an alternative solution and is then used in a set of parametric study to evaluate LSP for four soils. Results suggest that the proposed model can reasonably predict LSP in expansive soils.

Studying the hydro-mechanical behavior of the unsaturated soils is one of the critical challenges in the geotechnical engineering field. Many researchers developed elastoplastic models for unsaturated soils in which special attention was paid to the water phase modeling. However, most of these models have limitations in terms of compatibility of the elastoplastic behavior of the soil skeleton, water phase, and air phase. Neglecting the compatibility between these three phases led to conflicting predictions for the behavior of the unsaturated soil. The coupling effect between the mechanical and hydraulic behavior of unsaturated soils can be clearly seen under undrained loading conditions since the soil suction variations is not externally controlled, but internally determined by the coupling requirement that water content is constant. Therefore, a constitutive model is required to predict the coupled hydro-mechanical behavior of unsaturated soils under undrained loading conditions in a consistent way. The modified state surface approach (MSSA) was first developed to study the unsaturated soils’ mechanical behavior only. Later, it was extended to consider the hydro-mechanical behavior. In this paper, the ability of the MSSA to predict the soil behavior under undrained loading condition was demonstrated. Therefore, the coupled MSSA is evaluated by comparing its predictions against the experimental results for unsaturated soils collected from the literature. A very good agreement (coefficient of determination is greater than 99%) was reached between the measured and predicted void ratios and degree of saturation.

Existing methods for measuring volume changes of unsaturated soil specimens during triaxial tests have several limitations. Recently a photogrammetry-based method has been proposed to overcome these limitations. Although this method has many advantages over existing methods, such as low-cost, high-accuracy, no requirements for camera positions, and so on, it relies on a commercial software PhotoModeler to detect coded targets which involves tedious manual correction of coded target IDs and thus is not efficient to use. The objective of this study is to make the abovementioned photogrammetry-based method simpler, faster, and more automated to use. To this end, deep learning aided detection method has been proposed for the automatic detection of coded targets. Image processing technique has been proposed to automatically correct coded target IDs without manual operation. Based on the coded target detection results, a photogrammetric computer vision 3D reconstruction approach also has been proposed to reconstruct the 3D models of the cylindrical soils sample. Validation tests have been performed to validate the proposed approach. It is shown that it has accuracy comparable to commercially available software, and the average difference between results obtained from the proposed method and commercially available software is 0.01 mm.

Triaxial tests have been widely used for evaluating the stress-strain behavior of both saturated and unsaturated soils, in which, the volume measurement is a very important component; however, existing methods can only measure relative volume changes during triaxial testing. Recently a photogrammetry-based method has been proposed to measure volume changes of both saturated and unsaturated soil. Although this method has many advantages over conventional methods, it still has one drawback: the incapability to determine the top and bottom boundaries of the soil sample in the triaxial testing. In order to overcome this limitation, a least-square optimization approach and 3D reconstruction of triaxial testing were performed using the photogrammetry-based method. Many validation tests have been performed to calculate the distance between the top and bottom boundaries that confirmed the accuracy of the proposed method. This proposed method demonstrated very high accuracy by comparing the results and the measured distance with a difference of 0.0807 mm.

Recent developments of energy piles and soil borehole thermal energy storage have increased the concern of the behavior of soils under thermal loads. Laboratory heating and cooling tests of soils are subject to the ambient temperature effect due to inadequate thermal insulation. Thus, the test data are prone to errors due to such boundary effects. A double-column soil test cell was developed, and the test results of dry sand showed 1-D heating was obtained in the inner soil column. In this study, the heat cell was modified that a hydronic heating exchanger was attached to the bottom of the column. The dry fine-grained sand was first tested to validate the measured temperature field with theoretical predictions. Then the coarse-grained sand was then tested to investigate its temperature performance. The results showed that both fine/coarse-grained sand can maintain 1-D heat transfer in the inner column cell. This test cell is promising to study the soil thermal and hydro behavior under controlled 1-D thermal gradients.

Visual approaches of interpreting travel time in bender element experiments may not yield the accurate interpretations in noisy signals, which are often the case in sandy specimens and unsaturated states due to a smaller area of contact between soil particles and the presence of air voids, respectively. Therefore, analysis of received signals in such cases is significantly challenging, requiring knowledge of the effective range of parameters that control the quality of signals. For this purpose, comprehensive sets of bender element experiments are conducted in a modified triaxial device on silty and sandy specimens to monitor the changes in signals clarity with the evolution in unsaturated condition. Experimental results indicate that signals transmitted through more uniformly graded sand specimens carry a higher amount of noise, which is due to the quality of contact between bender elements and soil particles. Regarding the degree of saturation, it is observed that unlike silty specimens, as sandy specimens become drier, the output signals tend to be increasingly distorted.

Dilatancy significantly influences the shear strength of soils, which is of paramount importance for geotechnical engineers, which is commonly measured in the form of dilatancy angle. Only a very limited number of studies have examined the factors influencing dilatancy of unsaturated soils. In this research, the results from a series of suction-controlled triaxial tests following conventional triaxial compression (CTC) stress paths at different suction levels and net confining pressures were utilized to study the variation of dilation angle of compacted silty soil specimens with matric suction and net confining pressure. It was also observed that for all selected approaches, an increase in matric suction resulted in an increase in peak dilation angle. An increase in net confining pressure resulted in a decrease in dilation angle. These experimental findings would aid in calibrating advanced constitutive models capable of accurately incorporating the effect of various stress states on the dilatancy angle.

Coal has been used for electrical power generation for decades. There are several hundred unlined coal ash ponds in the United States that require closure. Federal regulations passed in 2015 also mandate assessment of the risk of leaching of coal ash constituents to the groundwater. Groundwater modeling is often required to assess such risk and requires a proper characterization of the saturated and unsaturated hydraulic properties of fly ash. This experimental study involved carrying out unsaturated hydraulic conductivity testing using the instantaneous profile method of fly ash collected from a coal ash pond located in southeastern United States. The unsaturated hydraulic conductivity function predicted by the van Genuchten-Mualem equation underestimated K(_ψ) at suctions greater than 10⁴ cm. The prediction function was relatively accurate at matric suctions up to 10⁴ cm. Thus, use of predicted unsaturated hydraulic function may underestimate the risk to groundwater.