Geo-Congress 2023: Soil Improvement, Geoenvironmental, and Sustainability

This paper presents the methodology and results of cradle-to-gate life cycle assessments (LCAs) performed for full-scale, root-inspired ground anchor (RIGA) prototypes, and conventional straight-shaft ground anchors (CGAs). LCAs performed in this study quantified the total environmental emissions of each ground anchor system in lb CO₂e emissions per anchor installed, for anchors anticipated to have equivalent ultimate capacities. Based on preliminary load-displacement pullout test results, comparison is made between a temporary 55-foot long CGA and a 38-foot-long RIGA. The CGA is estimated to emit 942 lb CO₂e, while the RIGA is estimated to emit 703 lb CO₂e per anchor, a 25% reduction. Material savings of 191 lb of cement and 28 lb of ferrous products per anchor are also expected. System boundary limits, manufacturing process assumptions, and assessment implications are discussed.

Alternative materials like biochar can be utilized to improve soil strength, while reducing the carbon footprint of soil stabilization through carbon sequestration. This paper studied the effect of various biochar/cement dosages on strength and stiffness of quick clay. Laboratory tests revealed that biochar quantities as low as 50 kg/m³ resulted in undrained shear strength, c_u, values (i.e., c_u = 2.8 kPa) greater than the 0.5 kPa threshold for remolded quick clay. Biochar amendment also enhanced c_u of cement-stabilized quick clay. For example, the c_u of quick clay samples stabilized with 25, 50, or 100 kg/m³ of cement increased between 20% and 40% when amending with 100 kg/m³ of biochar. Depending on the cement quantity, an optimum biochar dosage of 75–125 kg/m³ was identified. A sustainability assessment indicated that biochar amendments >30% of the used cement rendered the soil stabilization process carbon neutral. The current cost of biochar was, however, found to be greater than its benefits for soil stabilization. This may change in future because of higher carbon prices or lower biochar manufacturing costs.

Using alternative binders to traditional lime-cement mixtures in deep soil mixing is studied with the objective of reducing the carbon footprint of this ground improvement technique. Two by-products, bioashes and steel slag, combined with cement, were mixed with quick clay to investigate the strength and deformation properties of the stabilized material, as well as the leaching of contaminants for its environmental characterization. Bioashes and steel slag are residual products from the wood and steel industry, respectively. Results showed that after combining bioashes or steel slag with cement into quick clay, the strength and stiffness of the original material increased. The by-products were below the leaching limits for inert landfills following the European regulation, when tested both individually and combined with cement and quick clay. These findings reveal that bioashes and steel slag may provide sustainable alternatives to lime or cement in soil stabilization of quick clays.

Pervious oyster shell habitat (POSH) units are a novel method for oyster reef restoration and shoreline protection. POSH units have a similar function to traditional reef balls but are constructed from recycled oyster shells and cement. So far, POSH units have been deployed at multiple sites in Northeast Florida, including Kingsley Plantation, which is part of the Timucuan Ecological and Historic Preserve. The function of the POSH units at the Kingsley Plantation research site is to promote oyster growth/recruitment and attenuate wave energy from boat wakes in effort to mitigate shoreline erosion. The purpose of this study was to utilize computational fluid dynamics (CFD), specifically Siemens’ STAR-CCM+, to examine the effectiveness of the POSH units at reducing shoreline bed stress at the research site. A model with a single POSH unit was created and run under two wave scenarios. Results indicated that a single POSH unit may reduce bed stress, but this reduction is likely minimal. However, secondary effects that may influence shoreline erosion were also observed. These effects will be explored in future research. In addition, the CFD procedure outlined in this study may be used with multiple POSH unit configurations in the future to assess overall effectiveness.

The recent advances in the construction of tunnels and subways in urban cities involve the use of tunnel boring machines (TBM). The use of TBM in Riyadh, Saudi Arabia, resulted in huge quantities of crushed limestone powder (≈3 million cubic meters) and generally treated as waste. This work is aimed at utilizing the fine portion of the crushed limestone (powder) as a cement grout material and its possible use in shotcrete and lining of the tunnel works. The suggested mixture can be an efficient replacement for the sand cement grouts or lean concrete used in tunnel lining. This material is expected to be cost-effective and environmentally friendly as less cement and sand need to be used. The proposed mixture was subjected to geotechnical and material characterization as usually conducted for materials of similar applications. Mixtures of cement:powder of ratios 1:1, 1:1.2, and 1:1.4 were examined at a water-cement ratio of 0.6. Curing was carried out for 7, 14, and 28 days. Compressive strength tests were performed, and stress-strain relationships were established at early curing times and full-strength development to determine the crack initiation development as a key driven factor of a tunnel collapse. The results were compared to sand cement grout to measure performance improvement. The modes of failure and shear zones developed during tests were studied. Moreover, the impact of the crushed powder content on the strength and stress-strain relationship was evaluated. Characterization of the material, including particle size and shape description of the selected powder, was determined, and aggregate quality and durability tests were evaluated. The strength improvement due to the introduction of this material is attributed to the interlocking nature of the angular shape of particles. The workability of the mixture can be improved using additives of plasticizers, and this will enable using less water-cement ratio. More studies and examinations are suggested on the composition and gradation of the crushed limestone powder obtained from the tunnel-boring machine.

This life cycle assessment analysis in the present study compares energy consumption, carbon footprint, and environmental damages for the retaining wall backfilled with natural sand and used foundry sand (UFS). Utilization of UFS contributes toward lowering environmental impact in terms of waste management, ecological sustainability, and monetary benefits. This study consists of two sections, i.e., retaining wall design for modified backfill parameters, followed by a life cycle analysis (LCA) comparison study. Index and engineering properties of natural sand and UFS are determined for the retaining wall design based on codal specifications. As the study is aimed at evaluating life cycle assessment for construction instances where alternate materials like UFS are utilized, production, transportation, and utilization of conventional construction materials have been taken into consideration, along with the disposal of waste materials. The impact of variation in the height and type of wall is also studied. Environmental impact categories such as cumulative energy demand, human toxicity, and resource and ecosystem impact are evaluated for the cradle-to-gate variant. The software tool openLCA is used for environmental impact studies where the Ecoinvent database is considered with a mid-point approach. Factors of safety against external and internal stability of walls for different cases are considered and found to be above permissible limits. The impact categories are significantly affected and depict a loss in values when the UFS mixture is used as a retaining wall backfill. This is because UFS introduction in sand reduces earth pressure leading to savings in natural sand, concrete quantity, reinforcing steel, and fuel quantity consumed by building machines and vehicles transporting construction materials. The study concludes that in all examined impact categories, an alternative material provides a significant environmental benefit than the conventional material without compromising stability. The results demonstrate that the use of UFS is very effective as a sustainable alternative to natural sand for the backfill of retaining structures.

Various mitigation approaches have been proposed to decelerate CO₂ emissions to the atmosphere. CO₂ utilization for the carbonation treatment of recycled concrete aggregates (RCA) is a new strategy to consume CO₂ to improve the mechanical and environmental properties of waste concrete materials. During the RCA carbonation process, chemical reactions of CO₂ with residual cement paste produce calcium carbonate (CaCO₃) and silica (SiO₂), which can enhance the mechanical properties of RCA. The treatment also improves the environmental properties of RCA by reducing the concentration of heavy metals in the RCA leachate water. This method, however, requires a good understanding of the carbonation process and the main parameters that affect the efficacy of CO₂ utilization. In this manuscript, a laboratory study on the CO₂ utilization and sequestration potential of carbonation treatment of RCA at various treatment conditions is presented. Additionally, the potential impact of this technique on the carbon footprint is evaluated based on the CO₂ consumption data.

Landfills are a major source of carbon emissions in the US. Landfills are required to comply with certain federal and state regulations, including meeting requirements for final cover systems (FCSs). Significant weightage must be assigned to carbon emissions in selection of FCS. A detailed quantification of carbon emissions for three landfill FCSs—(1) soil cover, (2) soil-geosynthetic cover, and (3) an engineered turf cover—is performed. The life cycle boundaries employed in the study are cradle to end-of-construction. Emissions are classified into three categories: (1) production, (2) transportation, and (3) construction. Emissions in these categories for each component of the FCSs are estimated. A comparative analysis of the emissions for the three FCSs is performed, and findings and results are discussed. A sensitivity analysis is performed relative to transportation distances, and results are presented.

Traditional construction of bridge approaches requires an enormous volume of aggregates. Because the materials needed for many of these projects require hauling from long distances, larger amounts result in increased construction costs and associated carbon footprint. Additionally, quarrying these huge volumes of aggregates has a destructive impact on the environment. As the push for sustainable construction increases, there is a need for more environmentally friendly construction materials. This study aims to assess the environmental benefits offered by using low-density cellular concrete (LDCC) as a substitute for granular fill materials for mechanically stabilized earth (MSE) walls used for bridge approaches. The life cycle assessment (LCA) technique is applied to appraise the global warming potential (GWP) for six LDCCs and two granular fill materials. LCA is conducted across three phases: material extraction, transportation, and construction of the selected fill material life cycle. The GWP is estimated for 250 cubic meters of fill materials. The estimated GWP of six LDCCs ranges from 46 to 118 tons of carbon dioxide equivalents (CO₂e), whereas the aggregates fill released 186 tons of CO₂e, and the soil fill caused 191 tons of CO₂e. Overall, the GWP reduction by substituting granular fill with LDCC is between 37% and 75%. LDCC construction requires lower transportation of raw materials to the construction site, resulting in a reduction of 80% of truck loads when compared to granular fills. The results from this work indicate that LDCC can be a sustainable replacement for the traditional granular fills; however, some design adjustments for MSE walls are necessary. The conclusions and outcomes generated from this paper will support practitioners in quickly assessing the environmental impacts of using different fill materials for MSE walls.

The use of water balance (WB) covers in landfills increased over the last decade because of its enhanced performance and low cost of construction. This type of cover system consists of a vegetated soil layer and a storage layer that stores precipitation until the stored water is either evaporated from the soil surface or transpired through vegetation. Water balance covers rely on the storage capacity of the soil layer, rather than the low permeability of the soil, to minimize percolation. The storage capacity of the soil largely depends on the cover thickness and the unsaturated soil properties of the cover soil. On top of that, the local climatic condition also affects the design of cover thickness. The objective of this study was to analyze the water balance components of the WB cover system and execute a performance prediction evaluation based on field monitoring results. To pursue the objective, six large-scale test sections (lysimeters) were constructed side-by-side with locally available fine-grained soil (CH), followed by field instrumentation including moisture and temperature sensors, tensiometers, dosing siphon, and a weather station at the city of Denton municipal solid waste landfill, Texas. From the field monitoring results, the required soil water storage (S_R) was determined. The results showed that percolation decreases with increasing cover thickness, and cover thickness is significantly influenced by the distribution of precipitation and the unsaturated properties of the cover soil. Based on the field monitoring results and laboratory investigation of the soil, the cover thickness varied approximately between 1,160 mm (3.8 ft) and 1,700 mm (5.6 ft) for widespread annual percolation for the covers constructed with fine-grained soil.

This study focuses on the coupled thermo-hydro-mechanical response of an advanced geothermal energy storage (AGES) system in a low temperature sedimentary basin. AGES systems are a relatively new sustainable and renewable energy approach, which can provide a cost-effective and reliable alternative to conventional geothermal systems by supporting grid flexibility. An AGES system operates by injecting heat from other renewable sources into the subsurface via existing wells to increase a target reservoir temperature. To investigate the heat storage properties of an AGES system, a two-dimensional model is developed using a two-dimensional numerical model based on finite element method where the fully coupled interactions of thermal, hydraulic, and mechanical processes are considered. A sensitivity analysis is performed to investigate the design parameters of the AGES system, including Young’s modulus, porosity, storage formation thickness, thermal conductivity, and injection rate on the operational performance. Results indicate that the thickness and injection rates are the most prevalent physical and design parameters influencing the operational response of the AGES system.

Chemico-osmotic diffusion tests have been widely used to determine the chemico-osmotic coefficient (ω) of soils and geosynthetic clay liners (GCLs). A modified device for chemico-osmotic testing has been developed, which offers the option to confine the specimen by a load cell to monitor the total stress, besides the commonly adopted approach (confinement by a blocked piston). Being the strain conditions slightly different between the two approaches (i.e., small-strain versus no-strain), comparative chemico-osmotic tests have been performed. A dense prehydrated GCL and a 20 mM KCl as source solution were used. Under the no-strain condition ω was 0.33. Under the small-strain condition ω was 0.31, and the total vertical stress changed from 59 kPa in equilibrium with deionized water to 22 kPa in equilibrium with 20 mM KCl. Therefore, very close osmotic coefficients were obtained, with the advantage of monitoring the vertical stress during the test when using the load cell.

Odor is a grave concern at the municipal solid waste (MSW) landfills. Hydrogen sulfide (H₂S) is one of the major odor causing components of landfill gas (LFG). Recently, a novel biogeochemical cover system has been proposed, which incorporates biochar amended soil to mitigate methane (CH₄) through biologic oxidation and basic oxygen furnace (BOF) slag to mitigate carbon dioxide (CO₂) and H₂S through geochemical reactions. Series of batch and small-scale column experiments were performed with BOF slag to evaluate the potential of slag to remove H₂S. In addition, large-scale column experiments were performed simulating biogeochemical cover profile consisting of BOF slag layer overlying biochar amended soil layer, exposed to continuous flow of synthetic LFG comprising 48.25% CH₄, 50% CO₂, and 1.75% H₂S (v/v). The BOF slag showed significant H₂S removal potential up to 30 g H₂S/kg BOF slag through batch and small column experiments. During large-scale column experiments, all the H₂S was removed in the biochar amended soil layer indicating significant H₂S removal potential in biochar amended soil. Since BOF slag also possesses significant H₂S removal potential, potential of biochar amended soil to remove H₂S adds to the overall H₂S removal potential of the novel biogeochemical cover system.

The high saline content of the incineration ash of the semi-aerobic landfill is one of the major geoenvironmental problems in Japan. The traditional way to reduce the salinity by washing with fresh water is not conceivable due to the high cost. In this research, an innovative bioremediation idea has been applied to reduce the salinity of landfill ash. Collective microorganisms have been equipped in the laboratory for bioremediation. A semi-aerobic landfill simulator has been used in the laboratory. It has been noticed that the electrical conductivity has reduced around 68% after two weeks of bioremediation. The pH value also reduced and became almost neutral (7) after two weeks. The generated gas during the bioremediation has been analyzed by using gas chromatography. A small amount of gas containing chloride has been detected during the bioremediation, which is thought to be the reason for reducing salinity.

In the present study, numerical analysis was carried out using the finite element method to investigate the effects of liquid injection on the slope stability of landfills for heterogeneous anisotropic waste conditions. The numerical model was validated with the previously published literature for homogeneous and heterogeneous anisotropic waste conditions. The leachate recirculation was simulated for two different methods, i.e., horizontal trenches and vertical wells, with varied injecting leachate recirculation pressures. Based on the analysis, the moisture distribution achieved by these two systems was evaluated using degree of saturation and pore water pressure, and their effects on slope stability were investigated. High-pressurized leachate injections have adverse effects on the stability of landfills. The pore pressure developed in the landfill due to leachate injection is greater for the horizontal trench system in comparison to the vertical wells. The degree of saturation in the top layers of the landfill was greater in the horizontal trench system as compared to the vertical well system. The recommended location of the leachate recirculation system is at about 30%–40% of the overall height of the landfill, measured from the top surface.

Microbially induced calcite precipitation (MICP) is a sustainable biological ground improvement technology that is capable of improving the engineering properties of soil. A laboratory study was conducted to investigate the influence of some key environmental parameters on the long-term engineering performance of MICP-treated sandy soil, including wet-dry cycles, freeze-thaw cycles, and acid rain conditions, and to study the effect of enhancement through fiber reinforcement and multiple MICP treatments. Scanning electron microscopy, unconfined compression strength test, CaCO₃ content, and mass loss measuring were conducted on treated samples. The results have shown that the strength of MICP-treated soil can be deteriorated by WD cycles. For FT cycle tests, the MICP-treated samples had better resistance at earlier stage, but the strength decreased severely along with more FT cycles. The MICP-treated samples were poor to resist acid rain erosion because of the dissolution of CaCO₃ in acid. Fiber reinforcement and multiple MICP treatments were conducted to improve the resistance of MICP-treated sandy soil under environmental deteriorations. Fiber reinforcement mainly enhanced the ductility of MICP-treated samples. The failure strain of fiber-reinforced samples reached 1.6% compared with unreinforced samples of 0.4% after five wet-dry cycles. Multiple treatments enhanced the durability of MICP-treated samples. The UCS of multiple MICP-treated samples had no significant reduction after wet-dry and freeze-thaw cycles. For quadruple MICP-treated samples, a 51.9% UCS still remained after 15 days immersed in acid rain solution with the pH of 3.5.

An investigation was conducted to systematically analyze the cation exchange characteristics of a conventional GCL as a function of time and concentration of hydration liquid under typical laboratory conditions. GCL specimens were hydrated using DI water and 2 mM, 50 mM, and 200 mM CaCl₂ solutions for 4 and 8 h, and 1, 2, 4, 8, 16, and 32 days. Significant and rapid variations occurred in the amount and relative proportions of the bound cations in the exchange complex of the bentonite for the relatively high concentration solutions (50 mM and 200 mM CaCl₂). The exchange complex was relatively unaffected in the tests with DI water and 2 mM CaCl₂ solution. The highest changes occurred in the Na⁺ and Ca²⁺ fractions with relatively low changes in K⁺ and Mg²⁺. The majority of the exchange processes were completed within days (approximately ≤8 days) at the high concentration hydration conditions.

Bentonite-polymer composites (BPC) have been developed for use in geoenvironmental containment projects where sodium bentonite (NaB) is likely to undergo adverse chemical interactions that degrade barrier performance. Although numerous studies have investigated hydraulic conductivity of BPCs, very little is known about diffusion rates through BPC. Thus, this experimental study measured solute diffusion through different BPC materials for calcium chloride (CaCl₂) source solutions ranging in concentration (C_o) from 10 to 100 mM. The five materials evaluated in the study were NaB (without polymer amendment), BPC 1%–4% and BPC 1–8% (BPC type 1 with 4% and 8% polymer, respectively), and BPC 2%–4% and BPC 2%–8% (BPC type 2 with 4% and 8% polymer). For dilute CaCl₂ solutions, all four BPCs exhibited lower D_a values (by half an order of magnitude) than the unamended NaB. For higher CaCl₂ concentrations (C_o = 100 mM) the BPC2 mixes still exhibited superior performance (lower D_a) relative to NaB, whereas the BPC1 mixes exhibited similar or in some cases higher D_a values than the unamended NaB. The results of the study enhance our ability to consider and predict the expected performance of containment barriers comprising either NaB or BPC for a range of ionic strengths.

The current paper evaluates the applicability of vetiver grass for water balance final covers (WBFC) in Texas. There has been limited research and application of vetiver grass for landfill WBFC although it is an approved final cover system for landfills. The objective of the paper is to simulate vetiver grass for the WBFC in arid and semi-arid regions in Texas, using computer program UNSAT-H. The paper evaluates the applicability of vetiver grass and estimates percolation through the landfill cover. The paper illustrates WBFC with vetiver grass provides adequate storage capacity in both arid/semi-arid regions in Texas. WBFC with vetiver grass for north Texas (semi-arid) has a storage capacity of 16.32 in. (415 mm), where the maximum required storage is 9.96 in. (253 mm); for west Texas (arid region) it has a storage capacity of 15.10 in. (384 mm), where the maximum required storage is 2.84 in. (72 mm).

Compacted soil is widely used as liners and covers in waste containment systems owing to its low hydraulic conductivity (k < 1 × 10^–9 m/s). The hydraulic conductivity is often measured in laboratories using flexible-wall parameters or in fields using a lysimeter or infiltrometer, which all require weeks or months to reach equilibrium. In this study, a machine-learning-based predictive model was developed to determine the saturated hydraulic conductivity of compacted soil using the random forest (RF) algorithm. A database was created to train and validate the RF model, which contains the hydraulic conductivity and 12 impact factors of 329 soil samples in North America. The 12 impact factors, covering soil physical properties, hydration characteristics, and compaction conditions, were used in the RF model. A multiple linear regression model was also constructed as a comparison, using the same database and impact factors. The RF model validation indicated that 92% of the predicted hydraulic conductivity has a discrepancy with the measured hydraulic conductivity of fewer than 10 times, and 100% fewer than 100 times. RF model has a higher precision in predicting the hydraulic conductivity of compacted soil than the multiple linear regression model.

Direct and indirect climate forcing emissions of 65 non-methane volatile organic compound (NMVOC) species, grouped into 10 chemical families, were quantified from five solid waste landfills in California over dry and wet seasons. Tests and analyses were conducted for various daily, intermediate, and final cover systems. Correlations were developed between direct climate forcing emissions and site-specific geotechnical properties. Direct and indirect NMVOC emissions across all landfills were significant, ranging from –1.62 × 10^–1 to 1.33 × 10² and from –4.53 × 10¹ to 8.53 × 10² Mg CO₂-eq./year, respectively. Direct and indirect NMVOC emissions were highest for the alkane chemical family. Strong correlations were observed between calculated NMVOC emissions and cover soil geotechnical properties, demonstrating that NMVOC emissions decreased with increasing clay content, total cover solids, composite void ratio, and composite gas-phase tortuosity. The test results can be used to develop strategic cover design and operational aspects to mitigate adverse climate impacts of MSW landfills.

Oil spills can cause significant negative impacts on the environment, economy, and society. Bio-remediation is recognized as the most sustainable and environmentally friendly remediation method. However, two problems limit its application: (1) oxygen is required and (2) treatment is slow. Biochar can solve these problems perfectly: (1) absorb oil from soil for immediate oil removal and (2) stimulate the growth of oil degrading microorganisms without oxygen. In this study, a series of lab-scale lab tests were conducted to investigate the effects of depth of the biochar barrier and test duration on the oil removal efficiency. After each test, the bacteria number was counted to understand the bacteria growth with and without biochar in oil-contaminated soils. Test results demonstrate (1) the absorptivity of biochar is 900%, (2) oil removal rate increases with the increase of barrier depth and elapsed time, and (3) biochar could stimulate the growth of bacteria by 3–10 times.

Soil pollution is one of the main causes of the declination of shells and other sea creatures that live in the tidal flat area in Japan. The geotechnical approach to clean the polluted soil by mixing it with sand and recycled waste glass is difficult as it can cause some problems to the natural habitat of the living creatures. In this study, the microbial fuel cell, which is a bioelectrochemical device, has been used to remediate the pollution. It has been observed that the acid volatile sulfide (AVS) of polluted soil has been significantly decreased by using the microbial fuel cell. The application of the microbial fuel cell has been increasing the flow of electrons inside the anode area and thus enhancing the activity of the sulfate-reducing bacteria and other geobacteria. The voltage generation has been monitored during the process and has been noticed a significant increase of the voltage with duration. Thus, microbial fuel cells can be used to solve the problem of soil pollution and make suitable inhabitants for living creatures, and at the same time, it can generate some bioelectricity to power the environmental monitoring sensors.

Microbially induced calcite precipitation (MICP) is a sustainable and naturally occurring biological process that harnesses the metabolism capabilities of bacteria to produce a cementation agent known as calcite (CaCO₃). This study is to examine the effects of different reaction environments on the mechanical behaviors of MICP-treated sand. The mechanical behaviors will be evaluated through unconfined compression stress (UCS) experimenting with samples at 3, 7, and 14 days of curing in positive pressures at three different magnitudes (0, 50, and 100 kPa) or negative pressures at four different pressures (0, –5, –15, and –25 in-Hg). The results showed that the UCS of MICP-treated samples decreased with the increase of positive pressure. As for the samples with negative pressure, a better mechanical performance was observed when the negative pressure is –5 in-Hg. The SEM image clearly illustrated the change of CaCO₃ crystal morphology under different treatment conditions.

Stone columns have been increasingly adopted as an environmentally friendly and cost-effective method for stabilizing and reinforcing soft ground embankments. This paper presents a coupled modelling using the discrete element method and continuum modeling approach to study the load-deformation responses of stone columns. In the coupled discrete-continuum model, a soft soil domain under an embankment is simulated by the continuum method (i.e., finite difference method—FDM), while a stone column is simulated by the discrete element method (DEM). A series of interface elements are introduced to facilitate the force-displacement transmission of both domains. The DEM transfers moment and contact forces to the FDM, and then the FDM moves displacements back to the DEM. The model is calibrated and further validated by experimental data. Contact force distributions and shear stress contours developed in the stone column and surrounding clay are captured to provide a better understanding of the load-deformation responses of the stone column from a micromechanical perspective.

The abundance of granular waste materials coupled with their successful reuse in construction fills has provided sustainable alternatives to a rather expensive quarried natural rock aggregate. This study focuses on the application of coal wash (CW) as an admixture to mitigate the undesirable shrink and swell characteristics of expansive black soils under unconfined compression loading. CW is a by-product of the coal industry that requires an enormous area of landfill for storage. These landfills pose a serious environmental problem because coal is still being produced in many parts of the world. A series of unconfined compression tests were conducted on CW-soil mixtures with and without wet and dry cycles; these wet and dry cycles mimic the shrink and swell characteristics of expansive soil observed in the field. Our findings show that cracking and shrinking impact the fabric of CW-soil over time, which reduces their shear strength. The incorporation of CW into black soil reduces its susceptibility to shrinkage and swelling during wet and dry cycles. The relationship between the shear strength reduction after repeated wetting and drying are proposed for consideration in the design. The study shows that the addition of CW can improve the geotechnical properties of expansive soils under unconfined compression and curtail the degradation of the areas used to store the CW.

The Georgia Ports Savannah Container Terminal is an approximately 430-acre new container terminal planned on Hutchinson Island. Hutchinson Island, located in the middle of the Savannah River, is a low-lying marshland known for weak soils and engineering challenges caused by the weak soils. The soil stratigraphy comprises 30–40 ft of very soft clays underlain by sands of variable thickness and density and stiff clay locally called the marl. The engineering challenges include large settlements, ground instability for slope and bulkheads, and down-drag loads on piles. To study the behaviors of the soft clays for the design of the planned development, we constructed two test embankments with wick drains. The instrumentation included settlement plates, settlement sensors in different strata, magnetic extensometers, standpipe piezometers, and embedded pore pressure sensors. The data from the instrumentation provides insights into the consolidation process of the soft clay layer. The paper presents the construction and instrumentation plans of the two test embankments and data from the monitoring. The field test results were used to calibrate the empirical correlations of soil compressibility and rate of consolidation from cone penetration testing (CPT) and laboratory consolidation testing.

In nature, not all soils readily meet specifications for engineering use. Therefore, improvement of soil engineering properties is one of the main concerns of a civil engineer. The results of an optimal experimental design of stabilization concept for clay and sandy clay for use as subgrade material in road construction are presented. Two soils classified as A-7-6 (29) and A-6 (2) in the American Association of States Highways and Transportation Officials (AASHTO) classification system, which have fair to poor performance characteristics for use as subgrade, were mixed with 2% ordinary Portland cement (OPC) as an additive with stepped concentration of a viscous liquid known as Base-Seal (LBS) that has calcium oxide content of 57% (i.e., 0%, 20%, 40%, 60%, 80%, and 100% BS) used as replacement of the determined optimum moisture content (OMC) for the untreated soil using the British Standard light (BSL) or standard Proctor (SP) compactive effort. The compacted treated soil was cured for seven days under laboratory condition at a temperature of 30 ± 2^o C before immersion in water for 48 h as recommended by the Nigerian General Specifications (NGS) for Roads and Bridges. The result of the X-ray diffraction (XRD) analysis showed kaolinite as the dominant clay mineral in both soils. The silica-sesquioxide ratios for the soils are 1.86 and 1.79, which are within the range of 1.33–2.00 specified for lateritic soils. The surface morphology of the treated soil using scanning electron microscopy (SEM) depicts some coating of soil particles by the LBS and OPC. The plasticity index values decreased from 36% to 16% and from 13% to non-plastic for clay and the sandy clay after treatment, respectively. California bearing ratio (CBR) value increased from 1% to 22% for the clay treated with 40% LBS–2% OPC mixture and from 3% to 31% at 20% LBS–2% OPC treatment for the sandy clay. Based on the results obtained it is recommended that 40% and 20% LBS mixed with 2% OPC be used for the treatment of A-7-6(29) and A-6(2) soils, respectively, for subgrade in low-volume road construction.

In this study, the effect of different calcium sources on microbial calcium carbonate precipitation (MICP) was investigated. Three calcium sources, including calcium chloride, calcium nitrate, and calcium acetate, were selected based on their applicability and solubility. The fall cone tests and triaxial consolidated-drained tests were performed at the same proportion of calcium to urea, 1:1, with the concentration 0.5 M, and single-phase injection. The results indicated that the uniformity of specimen was increased by controlling the pH value of MICP treatment solution at 8.50–8.70 before injecting the solution into the specimen. Calcium nitrate exhibits the highest calcite content in treated specimens. On the consolidated-drained triaxial tests, peak strength is positively correlated with calcite content at confining pressure 100 kPa. However, calcium chloride specimens showed the lowest penetration depths in the fall cone test, which may be due to the matric suction under partially saturated condition. It may be concluded that saturation affects the effectiveness of improvement of different calcium sources.

In practice, pile foundation installation is accompanied by vibration and noise. Furthermore, structural faults along the pile may emerge if the surrounding ground has greater strength and damping than expected. Due to its sufficient strengthening and low environmental impact, biopolymer-based soil treatment (BPST) has recently been recognized as a new ground improvement technology. Because most biopolymer hydrogels have a shear thinning rheology, we conducted an experiment to see whether biopolymer hydrogels could mitigate pile penetration resistance when driving piles after installation. A pile model (40 mm in diameter × 740 mm in length) capable of measuring total resistance and tip resistance simultaneously has been fabricated for laboratory experiments. A biopolymer hydrogel spraying system, which consists of a two-way nozzle near the pile-ground interface on the surface, tubing for hydrogel transport, and a precision syringe pump for flow rate-controlled injection, has been introduced in this study. The pile model was penetrated into a pluviated sand chamber (380 mm in diameter × 900 mm in depth), with and without biopolymer hydrogel spraying during pile penetration. After pile installation tests were conducted at various times to determine when the injected biopolymer hydrogels should smear into the surrounding ground and improve pile-soil interaction. As a result, it was confirmed that the resistance to penetration of the model pile was reduced by about 17%.

Partial drainage occurs because of inevitable radial flow from the clay to the columns during foundation loading. Ignoring the positive effect of partial drainage on the short-term stability of foundations on reinforced clay may lead to over-conservative design. The objective of this study is to investigate the impact of partial drainage on the triaxial response of soft clays reinforced with sand column groups. Three partially drained tests were performed on large-diameter reinforced clay specimens under different strain rates to model different levels of partial drainage. The soft clay specimens were reinforced with a group of four dense sand columns. The drainage conditions were designed to restrict the dissipation of pore water pressure to radial flow. Results of the partially drained tests are compared to the baseline fully drained and fully undrained counterparts. Results focus on the effect of partial drainage on the stress-strain response, excess pore water pressure, and volumetric strain during shearing, in addition to the stress concentration ratio between the granular columns and the matrix clay layer. It was realized that the partially drained tests were bracketed between the fully drained and the fully undrained tests that served as upper and lower bounds for the strength of the composite, respectively. Interestingly, the results showed that a ratio of t_failure/t₅₀ of 15 seems to be a practical ratio at which the drained strength is mobilized in partially drained tests. Stress concentration ratio results for partially drained tests showed response also bounded between the drained and undrained scenarios, with an average stress factor in between 2.0 and 5.0. The results from the test program will improve the current understanding of reinforced clay systems response and potentially improve existing design methodologies.

Efforts to minimize energy loss during soil improvements have resulted in the emergence of environmentally friendly and sustainable biological process, termed biocalcificaion (or microbial induced calcite precipitation, MICP). Biocalcification technique was applied on a loose and wind-susceptible semi-arid zone soil of low strength for fugitive dust control process. The soil was treated with varying non-pathogenic urease positive Bacillus megaterium (B. megaterium) suspension densities (i.e., 1.5 × 10⁸, 6.0 × 10⁸, 1.2 × 10⁹, 1.8 × 10⁹, and 2.4 × 10⁹ cells/ml) and cementation reagent concentrations (i.e., 0.25, 0.5, 0.75, and 1 M) using different treatment cycles of 1, 2, and 3 and at a mix ratio of 50:50 (bacteria:cementation). Peak unconfined compressive strength (UCS) value of 453 kN/m² was obtained for soil compacted with standard Proctor energy and treated (in three cycles) with B. megaterium suspension density of 1.8 × 10⁹ cells/ml and 1 M cementation reagent. The urease activity and calcite content increased with higher bacteria/cementation contents that indicates the potential of the biocalcification technique for the improvement of the semi-arid zone soil considered in the study.

During the past 40 years, ground improvement has become a valuable tool for the geotechnical community, as the number of sites with suitable bearing soils becomes fewer and farther between. Similarly, as time moves on, more sites come into focus for development that have received any number of various landfill materials, be it municipal solid waste (MSW) from households, construction and demolition (C&D) debris from construction activities, or simply soil materials exported from another site. As a result, the challenges to engineers and contractors to design and construct new developments within budget and on time continue to increase. Dynamic compaction is a ground improvement technique that has been used more frequently to improve in-place landfill materials to a point where vertical construction can proceed without excessive long-term settlements. On sites where dynamic compaction is used, alternative methods of post-improvement evaluation have become more common, given the number of below-grade obstructions at a site that typically prohibit standard drilling approaches. Embankment load testing, plate load testing, and where applicable, post-improvement drilling are all techniques that have been used successfully to evaluate the effectiveness of dynamic compaction programs, as outlined by the three case studies discussed herein.

Biopolymer-based soil treatment (BPST) research has recently gotten much attention for environmentally friendly and sustainable soil treatment and ground improvement. The xanthan gum (XG) biopolymer, for example, has a high level of competitiveness due to its effective soil strengthening and hydraulic conductivity control properties. Even though XG improves soil strength by building tensile biofilms among soil grains, its high hydrophilicity causes rehydration of biofilms, resulting in a loss in strength in the presence of water. In this study, we used trivalent chromium cation (Cr³⁺) induced XG cross-linking to improve the strength and durability of XG-Cr³⁺-treated sands. The unconfined compressive strength and cohesion of sand are all increased by the time-dependent gelling effect in XG-Cr³⁺. Furthermore, XG-Cr³⁺ cross-linking shows sufficient improvement of the XG resistance to water exposure, resulting in increased durability even under long-term submergence. This study found that Cr³⁺ induced cross-linking enables to overcome challenges of pure XG-soil treatment, and XG-Cr³⁺-soil treatment can be utilized as grouting material since long-term strength can be achieved even underground without further dehydration and heat treatment.

Due to the changing climate, the rainfall duration and intensity increase each year. Especially in urban areas, the increased impervious surfaces (roofs, pavements) augment the surface runoff. Therefore, it is desirable to examine ways of increasing the soil hydraulic conductivity in a controlled manner and of reducing the runoff. In this study, we investigate the impact of the poly-vinyl alcohol (PVA) on soil hydraulic conductivity. The examined soil is poorly graded sand with clay (SP-SC). We use mixtures with 3% and 10 % PVA and employ a field test method for the measurements. We examine the suitability of the method for our measurements. The trends of the hydraulic conductivity observed match those found in literature for soil without PVA. Our preliminary results show that although the PVA does not significantly increase the overall soil’s hydraulic conductivity, that is the ability of water to pass through soil, the hydraulic conductivity increases at the early stages of the PVA’s dissolution.

Biocementation using microbial induced calcite precipitation (MICP) is a newly introduced and promising soil stabilization technique. In this process, ureolytic bacteria hydrolyze urea to give carbonate ions, which when combined with calcium-rich solution produces calcium carbonate that binds the soil particles together. The amount of calcite precipitate formed depends upon the pore size and hydraulic conductivity of the soil (keeping other factors the same). As the particle size decreases, the pore size and hydraulic conductivity both decrease, and hence the amount of induced calcite precipitate reduces. But the efficiency of this process not only depends on the amount of calcite precipitated but also depends upon how these precipitates bind the soil particles. In this study, the effectiveness of MICP on sand-clay mixtures of different proportions is investigated to find out the optimum gradation of sand-clay mixture for maximum efficiency of MICP treatment. A series of experiments were conducted to determine the unconfined compressive strength and induced calcium carbonate content of both treated and untreated clay-sand mixtures at various proportions. Test results indicated that as the amount of clay content increased in sandy soil, the size of the pore and hydraulic conductivity both reduced, leading to a reduction in the amount of induced calcium carbonate precipitation. The UCS of the treated samples showed better strength than the untreated samples. A post-treated sample with 20% clay soil shows 200 kPa more than an untreated sample of the same clay percentage. The improvement in strength between treated and untreated samples was reduced significantly after increasing the percentage of clay in sandy soil. At a higher amount of clay content, the MICP is restricted due to the improper growth of ureolytic bacteria and a lack of pores. The test results from this study provide an opinion about the applicability of the MICP on soil containing a significant amount of clay.

The objective of this study is to conduct a laboratory-based assessment of microbially induced calcium carbonate precipitation (MICP) as a viable approach to improving substructures beneath existing asphalt and concrete roadways. This was evaluated through unconfined compressive strength (UCS) testing, which can be correlated with the resilient modulus for subsurface samples to assess the degree of strength improvement achievable by the treatment. The calcium carbonate (CaCO₃) distribution is a critical component of this study. Three different injection methods were adopted to investigate the effect of injection method on (1) the treatment efficiency of soil specimens and (2) UCS and failure mechanism of bio-cemented sand, using Sakrete medium commercial sand. The efficiency of the different injection strategies was tested using an acid digestion method, used to determine the CaCO₃ content at different locations of the treated samples. Results concluded that samples injected in a top-to-bottom direction had better efficacy in terms of strength and uniformity over the alternatives.

One of the difficulties for the application of microbial induced carbonate precipitation (MICP) or enzyme induced carbonate precipitation (EICP) for soil treatment is to ensure uniformity in the treatment across the whole soil sample or soil profile. Methods that can be adopted to improve the uniformity of MICP or EICP treatment are reviewed and compared. Experimental data are presented to demonstrate that a newly proposed one-phase-low-pH injection method enables better uniformity to be achieved among different methods. Other factors affecting the uniformity of treatment are discussed. Measures to be adopted to enhance the uniformity of MICP or EICP treatment in sand are suggested.

The resilient modulus (M_R) of subgrade soil is a key parameter for mechanistic-empirical pavement design of flexible pavements. Generally, M_R is determined by conducting repeated load triaxial (RLT) tests in the laboratory and is used to characterize the subgrade soil behavior under repeated traffic loading conditions. This research study investigated the influence of compaction energy and moisture exposure on the resilient moduli of untreated and cement-treated cohesive soil. For RLT tests, untreated and cement-treated cylindrical specimens were prepared at respective optimum moisture contents and maximum dry unit weights, obtained from both standard and modified Proctor compaction tests. Compacted cement-stabilized soil specimens were cured in a humid room for seven days before they were subjected to RLT tests. Three-parameter universal model constants (k₁, k₂, and k₃) were determined by performing statistical regression analysis on RLT test results. Test results indicate that the compaction energy has a major impact on both the resilient moduli and stress hardening/softening behavior of untreated and cement-treated soils. The untreated soil specimens of standard Proctor compaction energy exhibited stress softening behavior with an increase in deviator stress, whereas the untreated specimens with modified Proctor compaction energy exhibited stress hardening behavior. In contrast, the cement-treated specimens showed stress hardening behavior with an increase in deviator stress, irrespective of the compaction energy. This might be because specimens tend to get hardened when subjected to higher axial loading, which resulted in low axial strains and exhibited high resilient modulus. Results show a slight decrease in resilient moduli of cement-treated soil after 4 h of submerging in water.

Microbial-induced calcite precipitation (MICP) is one of the bioengineering approaches explored in the last decades for engineering applications such as slope stabilization, liquefaction, and soil erosion. The bio-cementation and bio-clogging properties in MICP-treated soil depend on the treatment sequence (TS) strategies and composition of MICP solutions, which can affect the uniformity of calcium carbonate precipitation and soil properties. The current study compared the seven treatment sequences (TS) for the MICP process with the surface percolation method for soil strength improvement. Results revealed that soil samples followed TS 1 through TS 7 demonstrated bio-cementation properties and showed suitable pH after the treatment. However, the degree of bio-cementation is significantly affected by the treatment sequence. The samples followed by TS 4 and TS 6 have shown adequate bio-cementation and higher unconfined compressive strength compared to other treatment sequences. The microscopic investigations on the specimens extracted from soil samples of TS 1 through TS 7 revealed that TS 4 and TS 6 have more uniform and effective CaCO₃ precipitation.

Many researchers have suggested lime treatment of class F fly ash to achieve the desired strength and durability for its use as fill material in geotechnical applications. However, stress-strain and pore pressure response of lime-treated fly ash under a saturated state has not been explored. In this study, shear strength, pore water pressure response, and durability of lime-treated class-F fly ash have been evaluated. Unconfined compressive strength of lime-treated fly ash was determined for different curing time periods (7–84 days). A series of consolidated undrained (CU) triaxial tests were performed, and a new procedure for saturation of lime-treated specimens was developed to ensure its B (saturation value) to be 0.95. This study was further extended to conduct the durability analysis for two cases: soaking under water and wetting-drying cycles. Lime-treated specimens exhibited improved strength and durability response. In addition, lime-treated specimens under saturated state showed higher dilative behavior and brittle response than untreated fly ash.

This study aimed to evaluate the potential of microbially induced desaturation (MID) to improve the compactibility of silty sands. Conventional soil compaction techniques for saturated silty sands often require either high compaction effort to achieve the desired results or even fail to reach aspired relative densities outright. A lab study was conducted on silt-sand mixtures with increasing amount of fines. The objective was to assess whether biogenic gas formation could be used as a pretreatment to increase the effectivity of soil compaction techniques. A two-stage method was carried out in which, firstly, a soil sample was desaturated by means of microbially induced desaturation (MID) through denitrification and, secondly, dynamically compacted using a vibrating table. The results of this method were compared to results acquired from dynamically compacting the same soil without pretreatment. The treated samples showed a considerable amount of swelling during the first stage as a result of gas formation. All treated soils were able to desaturate below the optimum water content. After compaction, the relative density of all treated samples with 15%–25% of fines was a factor 1.5 to 2 times higher compared to untreated samples using the same amount of compaction effort. At higher or lower fines content the MID pretreatment was less effective. The results of the lab tests provide proof of concept that MID through denitrification can be used as a pre-treatment method to achieve higher degrees of compaction on silty sands. Further scale-up is still required to evaluate the full potential of this method at field scale.

This paper presents a novel, bio-treated solution to mitigate and control ice formation in frost-susceptible soils. Cold shock proteins (CSPs), which can be found in specific organisms like bacteria, fishes, insects, and plants, have the potential to lower the non-equilibrium freezing temperature of their bodily fluid. Silt, a very high frost susceptible soil, and three different strains of psychrophilic microbes, which release CSPs, were selected to test the hypothesis that the phase changes of porous media in silt can be controlled using the inherent survival mechanisms of psychrophilic microbes. Basic soil and CSP characterization tests were performed. Non-equilibrium freezing point depression and thermal hysteresis (TH) were measured for every treated and untreated soil to understand the effect of the CSPs. It was observed that a significant amount of freezing point depression had taken place with a concentrated number of psychrophilic microbes provided. Varying thermal hysteresis was also found in the samples, which also proves that the CSPs are contributing to controlling the ice crystal growth. Optical microscopic image analysis shows that the use of different psychrophilic microbes also changes the shape of ice formation. This research highlights a novel, bio-mediated approach to controlling the phase changes of porous media in frost-susceptible soils.

The present research has made an effort to support the subgrade strength performance of polyvinyl alcohol fiber-reinforced (PAF) soft soil stabilized with an alkali-activated stabilizer (AAS). The research compares the subgrade stiffness parameters (resilient modulus, penetration, and flexural resistance) between hydrated lime and alkaline stabilizer mixed PAF-soil at various slag/bagasse ash (BA) proportions. The influences of slag, BA, and PAF changing percentages in the AAS-soil matrix on the California Bearing ratio (CBR) and soil-beam flexural strength (Sf) are evaluated. The study also proposes an optimum dosage of slag-BA-PAF in alkaline stabilized soft subgrade soil. It is observed that PAF-AAS soil exhibits higher interfacial interactions and inter-bonding density than lime-PAF-soil under low tensile cracking. The combined PAF (0.6%) with 20% BA replacement with slag in the alkaline stabilizer strengthens the CBR and flexural strength by around 45% over lime soil-fiber mixtures. Moreover, a detailed reliability index (β) was also conducted to evaluate further the impact of uncertainties in the PAF-AAS-soil mixture on subgrade performance. The research study shows that the higher percentage of PAF-slag in a BA-based AAS mixture can substantially improve the stiffness and durability of soft subgrade soil.

The effectiveness of the biopolymer Rhizobium tropici for use a soil additive to improve vegetation drought resistance is described. Rhizobium tropici (ATCC 49672) is a gram-negative, aerobic, rod-shaped bacterium that attaches to plant roots and is responsible for nitrogen fixation. The bacterium uses plant sugars to produce an extracellular polymeric substance (EPS), or biopolymer that can form a hydrogel. The EPS was produced using 111 Rhizobium X Medium (ATCC). The structure of the biopolymer was observed using SEM cryo-microscopy imaging. Dependencies of the spatial properties of the gel network were observed. Hydrogel structures with coiled structure providing reinforcement and a bimodal distribution of mesh sizes were typical. The bulk soil properties of plastic limit and compactibility were measured for biopolymer modified and non-biopolymer amended soils, and the presence of biopolymer in these systems resulted in changes to these properties. The change in the bulk soil property compactibility resulting from biopolymer amendment showed significant changes at biopolymer loading rates as low as 0.0025% by dry weight. The hydroscopic property of the biopolymer hydrogel was observed through thermogravimetric analysis to show a fraction of strongly adsorbed water. Modification of the bulk soil properties plastic limit and compactibility using biopolymer indicate that this biopolymer may be well suited to improve slope stability, surface erosion resistance, and vegetation drought resistance.

Lime stabilization is used worldwide to enhance the engineering properties of problematic clayey soils; however, exposure to moisture has a detrimental impact on the longevity of lime-stabilized soils. A research study was designed and conducted to investigate the impact of stabilizer dosage and curing time before moisture intrusion on the durability and recuperative properties of lime-treated expansive soils. The soil was treated at optimum and optimum + 2% lime dosages. The stabilized soils’ behavior, before and after capillary soaking, was studied based on the strength and volume change properties of the specimens cured for 0 (6 h), 3, 7, and 28 days. The unconfined compressive strength tests were performed to study strength characteristics after moisture exposure. Furthermore, the soaked specimens were air-dried to pre-soaking moisture contents, cured again, and then tested for strength properties to study the stabilized soils’ recuperative properties. These results were also corroborated by supplementary mineralogical and microstructural studies. Test results indicate that the stabilized soils were able to completely recover from the moisture-induced damage only when exposed to moisture intrusion within a specific time window after treatment, the duration of which was governed by the stabilizer dosage.

In this work, the mechanical properties of three frost susceptible soils are investigated after treatment with organosilanes (OS). Compaction and strength characteristics tests are carried out on treated and untreated samples by means of a Harvard miniature compaction apparatus and a pocket penetrometer, respectively. The soils were treated with TerraSil, initially diluted at a ratio of 1:100 (OS:water) batched gravimetrically. It was determined that there was an overall decrease in optimum moisture content (from 1.07% to 2.26%) with samples treated with TerraSil. The influence on density varied with soil type, with modest increases (from 1,776 kg/m³ to 1,808 kg/m³) for one soil (Keokuk County) with a measurable plasticity index. The penetrometer results showed similar trends for the treated and untreated samples. The treated samples had slightly lower compressive strength overall. The most significant strength decrease (from untreated to treated for the same moisture content) for Ashe County was from 5 kg/cm² to 3.167 kg/cm², Hanover from 5 kg/cm² to 4.5 kg/cm², and Keokuk County from 2.75 kg/cm² to 2 kg/cm². These results are expected to be useful for engineering applications of TerraSil.

Erosion causes severe damage to the structural integrity of infrastructure; hence, the erosion resistance of soils is one of the most crucial design requirements for the construction of water-nearby facilities. This research suggests using biopolymers, organically oriented polymers, to reduce the surface erosion of soils caused by flowing water due to their potential to improve the hydraulic and mechanical properties of soils. Using the erosion function apparatus (EFA), which replicates a laminar flow velocity of 0–5 m/s, we determined the resistance of biopolymer-treated soils to flowing water, with embedded P-wave reflection sensors recording the eroded height to flow durations. The experimental results revealed that biopolymers significantly affected erosion control by enhancing particle contact, decreasing permeability, and filling pore spaces. In addition, biopolymer treatment significantly improved the critical shear stress and decreased the erodibility coefficient of soils. This research established a significant basis for suggesting biopolymers as stabilizers for river and seabed soil.

The wet method of deep mixing constructs soil-cement columns by mixing soft soil with cement-water slurry to improve the ground. A research project is underway to investigate factors that control the strength of soil improved by cement and to develop a framework for quantitatively accounting for these factors. As a first step of the project, this paper presents unconfined compressive strength (UCS) test results for cement-treated soil with different mix proportions cured at various constant temperatures. A fabricated low plasticity clay (CL) was blended with cement-water slurry and cured in an environmental chamber at low temperatures (–5, 0, and 5°C); other samples were cured inside a temperature-controlled water bath at a high temperature (45°C). Reference samples were cured in a humidity-controlled room at room temperature (21.1°C). UCS tests were conducted on the cured samples at curing times of 3, 7, 14, and 28 days. The test results show that when a curing temperature is 0°C or higher, an increase in temperature increases the strength of cement-treated soil. Furthermore, the strength rapidly increases at early curing stages and slowly increases at later curing stages. The strength development trends are affected not only by curing time and temperature but also by mix proportions. Cement-treated soil with more cement and less water had a concave curve in the curing temperature and UCS relationship, such that strength increases with increasing curing temperature rapidly at a low-temperature range and slowly at a high-temperature range, while a convex curve was observed for the mixture with less cement and more water. At a freezing temperature (–5°C), the strength development with curing time was not remarkable, and strength drops and relatively significant scatters were observed from the mixtures with more cement and less water.

With the advancement of civilization, building structures on weak foundation soil has become essential nowadays. When structures are built on weak foundation soil, they are subjected to bearing failure and excessive settlement. Most of the conventional ground improvement techniques are expensive, and they use virgin materials. The use of recycled plastic pins (RPPs) is a low-cost solution that can reduce the environmental effect of using virgin material and enhance sustainable waste management systems. The objective of this study is to quantify the increase of the strength behavior of weak foundation soil reinforced by RPPs. RPPs having two different cross-sections (100 mm × 100 mm, and 150 mm × 150 mm) were installed in the field at different spacings. Since RPPs were driven into the soil, the surrounding in situ soil got displaced and compacted. Dynamic cone penetrometer (DCP) and soil penetrometer were used to evaluate the material properties of the in situ soil. The strength properties of the improved soil were determined by laboratory investigation and also using the correlation between the shear strength of soil and dynamic cone penetration index. It was observed that the shear strength of the reinforced soil increased significantly compared to that of the unreinforced soil due to particle densification. This indicates an upward shift of the failure line of the reinforced soil. On the other hand, being stiffer material, RPPs carried a higher load, and the soil between RPPs was subjected to less stress due to soil arching action. Therefore, the stress paths shift downward, and the factor of safety of the reinforced ground against failure increases.

The use of recycled materials such as iron filings in soil improvement has become a growing interest due to the improved sustainability and decreased cost over the use of new materials. Currently, materials are mixed with soil or pressure injected to create chemical reactions (i.e., bio-remediated or lime-treated soils); however, there is little control over the resulting soil fabric. Magnetic fields have been used to align single-wall carbon nanotubes and graphene to create membranes and films and to reinforce synthetic composites, however, have not been previously used in soil improvement. This research investigated the effect of mixing ferrous particles (iron filings) in sand and using a magnetic field to rotate the particles to resist loads by increasing the soil strength. A series of consolidated drained triaxial compression tests were conducted to investigate the sand-particle mixtures by controlling the magnetic particle orientation. Two different relative densities (50% and 70%), two particle concentrations (5% and 7%), and five magnetic field strengths were used to create the iron filing particle mixture specimens. Results indicated that the 7% iron filing particles reinforced sand specimen prepared at 50% relative density had a strength increased by 25.1% compared to the non-rotated/randomly distributed iron filing particle reinforced sand specimens.

The use of industrial waste in civil applications can result in a sustainable and cost-effective alternative for the waste management of these steel by-products, provided that the engineering properties of these materials are comparable with those of other soil improvement additives. Recent studies in ground improvement have focused on using waste/by-products as additives to improve soils, decrease costs, and improve sustainability of projects. This study investigates the influence of randomly distributed ferrous particles (steel slag, iron fillings, and graphene flakes) within Ottawa sand specimens. Direct shear tests were performed on the samples prepared with pure Ottawa sand and the mixture of Ottawa sand with ferrous particles. Four particle concentrations (0%, 3%, 5%, and 7%) and two relative densities (50% and 70%) were used to prepare soil-particle samples. Results indicated that the addition of randomly distributed steel slag and iron fillings increased the shear strength up to 18%; however, the use of graphene flakes decreased the strength of the mixtures.

Enzyme induced calcite precipitation (EICP), as a bio-cementation technique, has been used to improve the strength and stiffness of unstable soils. In this paper, the influence of key treatment conditions for EICP soil treatment such as curing temperatures (at 5°C, 25°C, 30°C, and 50°C) as well as post-treatment conditions such as “oven-dried” (at 60°C) or “wet” (at room temperature, ~22°C) on the strength of EICP-treated sand were evaluated. The results from this study indicate that unconfined compressive strength (UCS), splitting tensile strength (STS), CaCO₃ content (C_C), the mass of precipitated CaCO₃ (${\mathrm{M}}_{{\mathrm{CaCo}}_3}$), and CaCO₃ precipitation ratio (PR) increased with increasing curing temperatures during EICP soil treatment possibly due to the increase in urease enzyme activity at high temperatures. For similar C_C, the “oven-dried” samples showed a significantly higher strength (i.e., UCS and STS) compared to the “wet” samples, possibly due to the transformation of unstable vaterite to a more stable form (i.e., calcite) during oven-drying. Scanning electron microscopy images and X-ray powder diffraction analysis showed that the “oven-dried” sample mainly produced calcite crystals, while the “wet” sample produced a mixture of calcite and vaterite crystals. The results indicate that thermodynamically unstable vaterite crystals formed at low temperatures may be transformed into a more stable polymorph of CaCO₃ (e.g., calcite) at high temperatures (~40°C to 60°C), an indication of the higher strength achieved for the “oven-dried” samples.

Organic matter in the soil makes a deep mixing project challenging since these organics interfere with cementitious reactions. It reduces the strength of cement-stabilized soil and/or delays the strength development, thereby requiring more cement to achieve the target strength of the project. A research program is ongoing to investigate the influence of organic matter on the strength of cement-stabilized organic soil and develop a framework for quantitative prediction of the strength of cement-stabilized organic soil. In our previous research, the effect of six organic compounds on the strength of cement-water slurry was tested, and tannic acid showed the strongest negative effect on the strength. This paper presents the finding of a laboratory study into the influence of organic matter on the strength of cement-stabilized fabricated clay with tannic acid. A fabricated lean clay (CL) and tannic acid at various concentrations were mixed with water and then blended with a cement-water slurry at various mix designs. The mixture was placed into a plastic mold and cured in plastic containers of water in the humidity-controlled room at room temperature for 3, 7, 14, and 28 days. After curing, unconfined compressive strength (UCS) test or laboratory miniature vane shear test was performed on cured samples. The test results show that the strength of cement-stabilized soil with tannic acid increases with curing time and the amount of cement added to the mixture, while it decreases with the increasing concentration of tannic acid. In this study, tannic acid proved its detrimental effect on strength development in cement-stabilized soil as well as cement-water slurry. In other words, tannic acid reduces the strength, but the negative effect of tannic acid is reduced by adding more cement or applying a longer curing time. Additionally, a threshold to overcome the negative effect of tannic acid was observed, and it was controlled by not only the amount of cement but also curing time and tannic acid concentration.

This paper presents unconfined compressive strength (UCS) test results of cement-treated soil cured under different curing conditions. During curing in water at different temperatures (21.1°C and 45.0°C), the samples for short-term curing were demolded at different times and then placed into the water again to continue the curing. UCS tests were conducted on all the short-term curing samples after an entire curing time of 28 days. On the other hand, for long-term curing, some samples were demolded at seven days and exposed to the water for further curing, while the other samples were sealed by a plastic mold during the entire curing period without any exposure to the water. The entire curing times for the long-term curing were between 100 and 400 days. The UCS test results showed that for the short-term curing, a sample demolded later and exposed to water for a short period was stronger than the sample exposed to water early. This trend was more evident at a high temperature (45.0°C), but the differences in the strength were small. For the long-term curing, a sample cured in the mold at room temperature (21.1°C) for the entire curing time had a higher UCS than the sample demolded at seven days and exposed to water for further curing, while there was no demolding effect at 45.0°C. The test results implied that a cement-treated soil sample cured in the mold can have a higher strength than a soil-cement column for the wet method of deep mixing that is exposed to materials around the column depending on curing conditions.

Trackbed stabilization (TBS) refers to engineering works to improve the railway trackbed stiffness in areas affected by poor load bearing capacity from soft subgrade. There are a variety of TBS techniques available to improve soft subgrades; however, many conventional approaches require a full renewal of the ballast which is disruptive and requires lengthy track possession time. This paper documents the improvements of a soft subgrade site in the UK using micropiles, installed between sleepers during overnight possession methods, thus allowing daytime rail traffic to run as normal. A non-contact vision-based monitoring (VBM) system developed by the authors and consisting of a high-speed camera was used to quantify the track bed deflection before and after the remedial works. The VBM system records displacement–time response of the rail and its foundation system during train passage. The results obtained from the experiments indicate that the post-rehabilitation trackbed modulus was increased.

Coastal bluff erosion and recession are among the common mechanisms altering the geomorphology of the coastline in California. The accelerated erosion rate increasingly threatens the stability of structures located on these bluffs. Previous researchers have investigated the effect of material properties and strength on the generation of the shear plane and failure modes of coastal bluffs and cliffs. Monitoring the morphology of the moderately cemented coastal bluffs with time has indicated that a comparison of material strength with the expected in situ minor principal stress distribution can be used as a criterion to assess bluff stability. However, the effect of varying factors such as cementation levels and bluff geometry and dimensions on stress distribution patterns and material properties that determine bluff failure susceptibility requires further investigation. While bond breakage and disturbance during sampling and transportation undermine the quality of recovered soil samples, artificial cementation methods (e.g., Portland cement) may not properly replicate the natural formation processes. Instead, microbially induced carbonate precipitation (MICP) is a ground improvement method that simulates the cementation processes that occur in natural geological settings. This method harnesses the activities of bacteria to generate cementitious precipitation among soil particles. The formation of the cementing agent improves the mechanical properties of the soil. In the past two decades, extensive studies have been devoted to understanding the cementation formation mechanism and the improvement of mechanical properties that can be used as a proxy for natural cemented soil for stability analysis. In the study presented herein, a series of FEM models were developed in SIGMA/W software. The effect of the different cementation levels and variation of bluff geometry on minor principal stress distribution was investigated. Results of the study demonstrated that although the cementation level of the materials determines the failure mode, the stress distribution mainly depends on the bluff geometry. The obtained results offer further insights into the failure mechanism of coastal bluffs as well as MICP-treated slopes for future field implementation of this soil improvement method.

Case studies of slopes experiencing unstable behavior under drained conditions below the stress level that would cause a traditional failure have been reported in the literature. Here, unstable behavior refers to a sudden collapse of soil resulting from a small change in stress conditions. This response, which is known as drained (diffuse) instability, is quite different from the widely recognized static liquefaction mechanism of failure for sand under undrained conditions. Microbially induced carbonate precipitation (MICP) as a soil improvement technique has a promising effect on the shear strength of soils and has potential to be used to reduce the potential of instability in granular slopes. To provide a better understanding of this collapse mechanism, a series of monotonic triaxial tests on treated and untreated specimens have been carried out to evaluate the effect of bio-cementation improvement on the instability under drained conditions. The experiments were conducted in two stages. Different stress conditions, including stress-induced anisotropy, were used for the first stage of loading. After that, a constant shear-drained (CSD) stress path was used in the second stage of the test as the mean effective stress was continuously reduced by decreasing confining pressure with a constant rate until instability was reached. The onset of instability in treated and untreated samples was investigated in this study.

The study sets out to investigate the use of rubber granules from used tires as solid (elastic) particles (without steel wires) mixed with conventional ballast aggregates for enhanced track performance (i.e., a rubber intermixed ballast stratum, or RIBS). The study evaluates the performance of RIBS subjected to both monotonic and cyclic loads by conducting large-scale triaxial tests for a range of rubber contents (0%–15%) under different confining pressures (10–60 kPa). It is evident from the results that rubber particles ranging from 9.5 to 19 mm with similar angularity to ballast aggregates are advantageous because they reduce the breakage of load-bearing larger aggregates, thus effectively controlling ballast fouling within the granular matrix while providing adequate resiliency. This project also demonstrated that particle densification at the conditioning phase can cause a reduction in permanent strains during the cyclic loads, thereby increasing track longevity.

Railways are an important part of infrastructure that work to deliver materials and people quickly across far distances with fewer emissions than transportation through vehicles in traffic. Damage to railways from seismic events can lead to train derailments due to deformation of the railway embankment. Previous experimental studies have shown that addition of tire derived aggregates (TDA) in the sub-ballast layer of railway embankments decreases the displacement of the embankment due to seismic loading. In this study, a finite element model is created to determine the optimum amount of TDA that can be added to the sub-ballast layer in order to improve the seismic behavior of railway embankments. Four models, conventional (100% sand), sand with 15% TDA, sand with 20% TDA, and sand with 25% TDA, are considered. The models are subjected to an earthquake loading, and the displacement and acceleration results of three points on the embankments are recorded. The obtained results indicated that addition of TDA in the sub-ballast layer reduces the maximum acceleration and maximum displacement of the railway embankment under seismic loading. As the optimum percentage of TDA, values around 20%–25% can be proposed for practical uses.

In recent years, there has been a push to incorporate sustainability metrics into geotechnical design decisions. Life cycle assessment (LCA) has become more broadly implemented in the field, as this allows practitioners to quantitatively evaluate environmental impacts associated with projects. This paper summarizes a comprehensive review of recent publications applying this method to various geotechnical systems, including deep foundations, ground improvement, earth retaining structures, and others. Results from each of these categories are discussed, with emphasis on exemplary studies conducted. Based on this analysis of recent geotechnical LCAs, current limitations are identified, and recommendations for future studies are made.

This research will investigate the use of a ground-source bridge deck deicing system, to remove snow and ice and mitigate temperature fluctuations within concrete bridge decks for Montana weather conditions. Temperature fluctuations lead to the deterioration of concrete. Damage from these fluctuations is especially prevalent in concrete bridge decks in Montana where there are many freeze-thaw cycles throughout the year. Time histories of weather data from 73 road weather information system stations throughout the state were collected over the period of 2015 to 2020 and used to develop a range of winter events to replicate in a numerical model. The numerical model of a bridge deck with embedded heat exchanger pipes was constructed in COMSOL Multiphysics and used to evaluate the feasibility of using a geothermal bridge deck deicing system when exposed to severe winter events. Results from a series of model bridge deck heating experiments available in literature were used to validate the numerical model. Preliminary results show that a geothermal bridge deck deicing system can successfully bring the bridge deck surface temperature above freezing during severe Montana winter events. However, ground-source bridge deck deicing systems will likely not eliminate the need for other snow and ice removal and prevention strategies. The most effective solution will likely include a combination of available methods.

This study provides insight into the application of geothermal energy to prevent thermal cracking in concrete pavements and bridge decks that may occur due to the high-temperature gradient. Two full-scale shallow geothermal boreholes were installed on the University of Louisville campus. U-shaped heat exchanger tubes were embedded inside both boreholes, and two demo bridge decks have been cast with concrete. Both geothermal boreholes are connected through a small trench to the demo bridge decks. A water/antifreeze mixture is circulated inside the heat exchanger tube, and the system solely depends on the constant ground temperature. Unlike the severe changes in ambient air temperature, the embedded tube showed an almost stable temperature. Temperature variations of the demo bridge deck connected to the geothermal borehole were limited and close to a near-constant ground temperature. Results confirm that a geothermal system can be used to cool the pavement surface even during hot summer days by reducing the temperature gradient in concrete, which may, in turn, reduce the risk of thermal cracking.

In this paper, the effect of hydraulic conductivity of RAP on drainage time and minimum required thickness of highway base layers was evaluated via DRIP (Drainage Requirement in Pavements), a US FHWA software. Seven RAP materials collected from various places within the state of Maryland were used in the analyses. In addition, their performance as a highway base material were compared with a traditional graded aggregate base material (GAB) and stone no. 57. The time-to-drain approach was employed to evaluate the drainage capability of RAP as well as the control materials. DRIP software helps to categorize the base material as poor, fair, good, and excellent based on the required time for 50% drainage of the infiltrating water. A series of analysis was performed to investigate the influence of drainage percentage U, base thickness H, and hydraulic conductivity k on time-to-drain. The results indicate that the fines content and hydraulic conductivity significantly affect the time to drain, particularly after 40% drainage. Furthermore, increasing the base thickness results in a drastic decrease in time to drain. When compared with the traditional base materials, it can be concluded that RAP materials yield satisfactory results for utilization as a highway base material in terms of drainage capabilities.

Hydrous and quick lime is utilized in various types of food processing operations to remove impurities from agricultural products. During this process, the waste that is produced consists of precipitated calcium carbonate, organic debris, and trace amounts of soil and contaminants. When used in large-scale operations, the waste can exceed 100,000 tons of waste per year per site. This waste material is not compostable due to its chemical composition and is of too large of volume to be sent to landfills. Hence, the waste is typically stockpiled on land adjacent to food processing facilities, which is not an environmentally or economically sustainable solution. Finding an environmentally and economically sustainable solution to utilize this waste material has the potential to save capital on construction projects as well as significantly save in land investment by food processing facilities. The food-processing waste described above usually contains commercially available unspent lime products, which are viable for construction applications. Lime stabilization using relatively pure quick or hydrous lime has been successfully used to improve the strength and swelling properties of expansive clays. This paper studies the utilization of the above-mentioned waste in construction where the organic content by weight is consistently measured at lower than 5%. Using a series of geotechnical and environmental laboratory testing procedures, several engineering properties (e.g., swell potential, permeability, leachate potential) are measured to find the right series of tests and appropriate target blends of construction material and food processing waste. Preliminary testing points to reduced swelling potential and increased density when a sample of the food-processing waste is mixed with an expansive clay. Once procedures have been standardized, using these materials in construction applications may also produce a secondary revenue stream for certain food processing facilities.

Sustainability is an inclusive concept that seeks to balance the three main pillars of economic, environmental, and social conditions. Today’s infrastructure needs require all architects, engineers, and contractors to make a concerted effort to select materials and construction practices that minimize carbon emissions. One widely accepted geotechnical fill material that can contribute to the sustainability of any project is low-density cellular concrete, or LDCC. LDCC is an engineered mixture of Portland cement, water, and preformed foam that results in a hardened material having an oven-dry density of 50 lb/ft³ (800 kg/m³) or less. LDCC can be selected to not only optimize performance in the field but also reduce the adverse CO₂ impacts often associated with its use. This paper will introduce emerging and traditional LDCC technologies as well as examine the vital role LDCC plays in the cement and concrete industries’ efforts to reach carbon neutrality by 2050.

The main objective of this study is to gain insights into the soil-water-vegetation-biopolymer interaction and how those interactions control soil hydro-mechanical properties. Four different sample types were prepared, including plain soil, rooted soil, biopolymer-amended soil, and biopolymer-amended rooted soil. After the development of a complete root system, several different hydraulic and mechanical tests were conducted to determine the effect of soil type on engineering properties. In particular, the hydraulic behavior of all samples was investigated by determining the saturated permeability, evaporation, and infiltration rates. Vegetated-biopolymer specimens showed lower permeability and infiltration rates compared to other soils. Finally, direct shear tests were performed to evaluate the shear strength characteristics. The results showed that any combination of the soil treatment led to a slight decrease in the cohesion values leading to deteriorated shear strength. These results are beneficial to engineers in better understanding of vegetation and bio-augmentation techniques and their implementations, especially in severe drought environments.

Lightweight structures founded on expansive soils can be affected by soil-atmospheric boundary interaction. For example, soils can go through significant volume change when subjected to changes in moisture content, causing ground movement. One of the approaches to incorporate the effect of atmospheric boundary interaction in geotechnical design is the Thornthwaite Moisture Index (TMI), which can be correlated with the depth of suction change (H_s), which is an important input to the estimation of ground movement. In this study, the long-term weather data and outcomes of global climate models were used to quantify expected changes in TMI, and then a series of H_s maps were developed for South Australia for different emissions scenarios. Under all scenarios, the state is likely to have a significant increase in H_s (an average increase of up to 0.7 m was observed under different future climate scenarios), and designs that are considered safe under the current climate may become insufficient and may even lead to ultimate failure.

The sustainability and resilience of geotechnical structures are essential to the performance of infrastructure systems. Objective assessment of sustainable and resilient practices requires quantitative approaches to measure vital characteristics of geotechnical materials and construction methods. Professional and engineering entities have proposed numerous frameworks for such measures, like environmental product declarations (EPD). This paper investigates the employment of EPDs in the appraisal of geotechnical structures like retaining systems. The proposed framework involves a life cycle approach to applying lightweight backfill using rotary-kiln manufactured aggregates. The life cycle analysis addresses significant phases of the project, beginning with mining, progressing through construction, maintenance, and retrofit, and ending with recycling and reuse. Elements of calculations include materials, equipment, and labor required for various phases. Discussions include a critical analysis of the results compared with other assessment techniques. Outcomes provide practitioners and scholars guidelines for employment, customization, and development of EPDs for geotechnical projects.