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Coal gangue is a mine waste generated during the mineral processing phase of coal production. With the surge in demand for coal in thermal power, steel and cement generation industries, the rate of coal gangue generation has reached unprecedented heights. With the realisation of potential threat posed by coal gangue, researchers have made attempts to explore many new avenues of applications for its bulk utilisation. Unfortunately, the implications of coal gangue utilisation on the surrounding environment have not been taken into consideration. In the present study, an attempt has been made to perform carbon footprint analysis on coal gangue to assess the CO2emissions in utilising it as an embankment material. A similar analysis is done to evaluate the emissions in its disposal process. The results obtained from both the analysis have been compared to assess the feasibility of utilising coal gangue in targeted geotechnical engineering applications. The studies corroborate the fact that the utilisation of coal gangue can lead to a significant decrease in the carbon footprints generation, thus leaving a positive impact on the environment.

The hydro-mechanical behavior of a material is an imminent criterion for assessing the performance of a liner and sub-base material. Several materials have been explored in the past including waste-derived products such as gypsum-treated fly ash, bentonite sand mixtures, and biopolymer-modified cohesive soils. The nonavailability of cohesive soils has shifted the focus on the amelioration of sandy soils to suit liner and sub-base requirements. This has prompted researchers to undertake the effect of fine contents on sands. The current study investigates the prospective of utilizing three Artificial Intelligent (AI) techniques to forecast the compressive strength (U) and coefficient of permeability (k) of the sand using the collected database. The techniques employed were Genetic Programming (GP), three models of Artificial Neural Networks (ANN), and Evolutionary Polynomial Regression (EPR). Among the three techniques, ANN exhibited a better performance in the prediction of compressive strength and permeability compared to GP and EPR with more than 77% and 97% of accuracy. Among the influencing parameters, gravel content did not pose a considerable effect on the prediction of permeability values. The research findings will aid practicing engineers to come up with better design mixes of finer fraction mixed sands for liner and sub-base material applications and monitoring and assessment of the performance of constructed liners and sub-bases for a healthy environment.

In this study, enzyme-induced calcite precipitation (EICP)-based treatment for tropical soils contaminated with divalent heavy metals such as cadmium (Cd), nickel (Ni), and lead (Pb) were evaluated for their sorption and desorption capabilities. Heavy metals were taken in three different combinations: a single metal and a combination of two and three metals. They were mixed with locally available kaolinite and montmorillonite soils. EICP-treated soil retained the maximum quantity of Cd among all the heavy metals studied. The Cd retention exceeded Ni and Pb retention. The same was confirmed with desorption studies, relying on aggressive chelants such as ethylene diamine tetra acetic acid (EDTA) and citric acid. Before subjecting the kaolinitic soil to EICP treatment, it was found that the sorption capacity for Cd and Ni was 2.124 and 1.974 mg/g for Cd and Ni, respectively. The sorptive values increased to 3.457 and 4.418 mg/g for Cd and Ni, respectively, after EICP treatment. The retention is attributed to the formation of CdCO3 and NiCO3 in the soil matrix, which exhibits very low values of solubility product even in the presence of aggressive chelants. The study establishes that EICP treatment is a prospective method for remediation of soils laced with heavy metal ions.

Biochar, a carbon-rich material derived from biomass through controlled or oxygen-limited pyrolysis, possesses remarkable resistance to biodegradation. Its versatile physicochemical properties have led to its widespread use in soil remediation, wastewater treatment, carbon sequestration, energy generation, and environmental mitigation. This critical review on select biochars highlights biochar production, considering factors such as temperature, residence time, heating rate, and feedstock type, which influence its properties. It is observed that for biochar production, utilizing abundant biomass resources is cost-effective and environmentally friendly. Furthermore, any biochar sourced from various materials like agricultural, industrial, and crop waste, wood, animal manure, and sewage sludge exhibits high porosity, specific surface area, and surface functional groups, facilitating its efficacy in addressing various challenges for diversified applications. The physicochemical properties of biochar, dependent on pyrolysis conditions and feedstock, necessitate a complex comprehension for targeted application. Moreover, the influence of biochar amendment on soil physicochemical characteristics is discussed. The efficacy of biochar and engineered biochar, in remediating soil contaminated with heavy metals, is compared. The role of biochar in geotechnical contexts is outlined. The current review appraises biochar's diverse applications, emphasizing its complex potential.

Unexpected volume changes manifested in the soil beds due to accidental release of alkalis from industrial establishments has become a major challenge. The neogenic formation that leads to volume changes due to physicochemical reactions between clay minerals and alkalis need to be addressed. The current article focusses on the possibility of using alternate by-products such as ground granulated blast furnace slag (GGBFS) and flyash (FA) for controlling the swell induced in alkali transformed kaolinitic clays, ATKC’s (i.e., red earth and kaolin). Results indicate that ATKC’s exhibited unexpected changes in swelling behavior upon inundation with water and alkali (4N NaOH) solutions. ATKC’s were later amended with FA and GGBFS to address the swelling phenomena. Marked reduction in swelling was noticed in ATKC’s with FA (10% and 20%) and GGBFS (10% and 20%). Reduction of about 40% of overall swelling was noted in alkali transformed red earth (ATR) when treated with 10% FA and 50% reduction with 10% GGBFS. Further, treatment of ATR with 20% FA and 20% GGBFS, decreased swelling to about 82% compared with ATR-4N. In case of alkali transformed kaolin (ATK), 57% and 56% reduction in swelling were observed with addition of 10% FA and 10% GGBFS, respectively. At 20% FA and GGBS content, reduction in ATK-4N swelling was 75% and 90%, respectively. Thermo Gravimetric–Differential Thermal Analysis (TG–DTA), X-ray Diffraction, and Scanning Electron Microscopy (SEM) analysis confirmed the alterations in ATKC are stabilized with FA and GGBFS.

Quality construction control requires ensuring that compacted fills are properly placed without any significant delay between mixing and compaction of the wet soil mixture. When chemical treatment is resorted to meet the shortcomings in the use of locally available materials, the delay in compaction (time elapsed between mixing and compaction of the wet soil mixture) plays a significant role as it dictates the final in-site density values achieved. In this study, the effect of delay in compaction on the density and moisture content relationships was evaluated for the delay periods of 1hr, 4hr, 24 hr and 7 days. The study was even extended to lime treated soils (at 2% and 4% by dry weight of soil). The time lag which occurs immediately after the onset of wet mixing and compaction often results in variation in geotechnical properties. Accordingly, an attempt was also made to study the effect of delay in compaction on the hydraulic conductivity, compressibility and unconfined compressive strength (UCS) behaviour of plastic clays sourced from the semi-arid region. In order to understand the variations in microstructure, MIP tests (Mercury Intrusion Porosimetry) were conducted at higher delay periods when treated with lime. From the results, it was observed that delay in compaction led to an increase in the hydraulic conductivity and compressibility of both soils. Furthermore, the UCS of both the soils showed a decreasing trend with the increase in the delay period. The agglomeration of clay particles leads to the formation of clods at higher delay periods which resist the compaction energy resulting in reduced density values which in-turn affect the geotechnical properties.

The soils in hazardous waste sites contain heavy metals which would leach into groundwater by various biotic and abiotic processes and eventually pose a threat to human health by contaminating the drinking water. In order to understand pattern of heavy metal leachability, the field conditions can be simulated by adopting various types of sequential extraction methods. In this study, an attempt was made to evaluate the effectiveness and selectivity of a sequential extraction process to determine heavy metal binding mechanisms in soils and soil treated with nano-calcium silicate (NCS). A five-step sequential extraction (SE) procedure was adopted on four soils obtained from a sanitary dumpsite, automobile and battery work units from different localities of Bangalore and a steel plant commissioned at Toranagallu, Bellary, India. The soils were mixed with NCS at varying range of 0.5 to 2% by dry weight of the soil. The NCS-amended soils were spiked with cadmium (Cd2+), nickel (Ni2+) and lead (Pb2+) in concentrations to the tune of 3000 mg/kg. It has been observed that there seems to be a gradual increase in binding ability for the targeted heavy metals when soils were amended with NCS compared to untreated soils. This binding phenomenon was attributed to the presence of exchangeable ions, carbonates, oxides of iron and manganese, organic matter and residual fractions. It was noticed that the residual fractions in soils amended with NCS attenuated maximum quantity of metal ions with Pb2+at 21.46%, followed by 18.8% for Cd2+and 9.25% for Ni2+compared to untreated case. Further, this work highlights the role of residual fraction in enhancing the retention capacity of soils by encapsulation of higher concentrations of contaminants. The current study corroborated the fact that the addition of NCS aids in the better encapsulation of selected heavy metal ions.

This article evaluates the desorption of heavy metals from lime-stabilized, contaminated semi-arid soils under harsh environmental conditions involving chemical extractants, specifically, acetic acid (CH3COOH), nitric acid (HNO3), ethylene diamine tetra-acetic acid (EDTA), and diethylene triamine penta-acetic acid (DTPA). In this study, heavy metals, such as arsenic (As), chromium (Cr), mercury (Hg), and lead (Pb), were spiked with two semi-arid soils (exhibiting different plasticity characteristics) at different load ratios (10–250 mg/kg); they were later stabilized with lime to evaluate the reduction in their mobility. Extensive desorption tests were performed on these soil mixtures to study the efficacy of lime for the in situ fixation of heavy metals. This study revealed that irrespective of the nature and size of the heavy metal, the removal efficiency for the soils was greater than 80%, and EDTA at a concentration of 1 M yielded the maximum removal efficiency. It was found that the cationic metal ions Hg and Pb were desorbed effectively by EDTA, while As was desorbed by HNO3and Cr by DTPA. The order of desorption for heavy metals was found to be as follows: As > Cr > Hg > Pb. The lime amended soils exhibited lower removal efficiencies (more than 48% retained) due to efficient retention of metals in the soil interstices, making them inert and immobile. There was an improvement of 40% in soils amended with lime compared with virgin soils in the case where soil washing by harsh washing agents was resisted; this proves that the contaminants were embedded in the interstices of the soil calcium interfaces. Therefore, this study asserts the notion that the mobility of heavy metal ions from brownfields can be effectively reduced by in situ lime treatment.

This study investigates the influences of sample size and dry unit weight on expansive soil properties, focusing on soil water characteristic curves (SWCCs) and the stability of unsaturated finite slopes. The expansive soil collected from IIT Hyderabad, Sangareddy, Telangana, India, was compacted in both California Bearing Ratio (CBR) and relative density (RD) molds at varying water contents, ranging from 8.0% water content to saturated water content. Soil water characteristic curves (SWCCs) were systematically measured at different depths using matric potential sensors (MPS) in both CBR (2 cm, 8 cm, and 14 cm) and RD molds (2 cm, 6 cm, 10 cm, 14 cm, and 18 cm). Notably, matric suction of the soil compacted in RD molds was assessed at the maximum dry unit weight (MDU), as well as at 90%, 80%, and 70% of MDU. The results of the experiments revealed that matric suction in the CBR mold was underestimated by 14.69% when compared to the RD mold. Moreover, expansive soils compacted at MDU exhibited 68.56% greater suction than those compacted at 70% of MDU. The study highlights the depth-dependent increase in matric suction in both CBR and RD molds. Furthermore, the research elucidates the pronounced hysteresis effect in expansive soil compacted at low dry unit weight compared to MDU. Crucially, the research establishes a robust correlation between the stability of unsaturated finite slopes and the dry unit weight. The factor of safety for unsaturated finite slopes exhibited an 84.67% increase as dry unit weight increases from 12.4 kN/m3to 17.7 kN/m3, emphasizing the significant influence of dry unit weight on location of critical failure surfaces. The present investigation provides crucial understandings into the complex interactions among soil compaction, matric suction, and slope stability. These findings offer valuable information for improving geotechnical approaches in slope design and management.

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation alternative for expansive soils in the presence of lime. California bearing ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fibre contents and longer lengths and the effect was prominent when lime was used as a stabiliser. There were some exceptions to this behaviour, which were noted in the paper. The probabilistic analysis showed that the amount and lengths of fibres were important factors in CBR strength. It was also determined that the variation in the target CBR value had a considerable effect on optimising the length and amount of the fibres.

Experiments have been conducted to study the effects of anisotropy and remolding on the soil water characteristic curves (SWCCs) of soils exhibiting different plasticity characteristics. The soil samples were collected from IIT Hyderabad, Sangareddy, Telangana, India. Anisotropy and remolding effects were quantified based on the factor of safety of unsaturated finite slopes. The combination of the Hydraulic Property Analyzer (HYPROP) for low soil suctions and the dew point potentiometer (WP4C) for the high suction range is employed to obtain the full range of SWCCs. The SWCCs of the remolded soil samples compacted at field density and water contents of dry of optimum (DOP) and wet of optimum (WOP) are estimated. The SWCCs are plotted using the data obtained from HYPROP and WP4C. The experimental results indicated that there is a profound change in the shape of SWCC when it is estimated using HYPROP and HYPROP along with WP4C data. Moreover, the SWCC fitting parameter afrelated to air entry value is underestimated from the SWCC, which is obtained employing HYPROP data. The fitting parameter (af) values of expansive clay obtained from HYPROP and HYPROP in conjunction with WP4C are 12.34 kPa and 3342.7 kPa, respectively. The present study suggests combining HYPROP and WP4C data to accurately estimate the SWCCs. Further, the investigations revealed that the SWCC fitting parameter afis higher in remolded soil compacted at WOP than at DOP. When the expansive clay is compacted at DOP and WOP, the values of the SWCC fitting parameter (af) are determined to be 9.54 kPa and 59.47 kPa, respectively. The SWCCs obtained from the remolded soils are compared with the SWCCs of the undisturbed soil samples. It is observed that the influence of anisotropy on SWCCs of clayey sand and expansive clay is minimal. The factor of safety (FoS) of unsaturated finite slope increases by 11% in clayey sands and 7.9% in expansive clays when water content changes from DOP to WOP. Moreover, the percentage increase in FoS is higher in the case of the flat slope. When the moisture content changes from DOP to WOP, percentages increase in FoS of expansive clayey slopes are 12.12% and 7.89% for slope angles of 35° and 50°, respectively. The FoS of the unsaturated finite slope is quite sensitive to the initial water content due to significant shifts in the location of critical slip surfaces.

Biopile treatment is a controlled organic cycle where biodegradable foreign substances are changed over to their fundamental mineral constituents (water and carbon dioxide) under oxygen-consuming conditions. The contaminated soil is excavated and accumulated in the treatment region. This uncovered soil is then framed into a pile which is termed as biopile, and the air is circulated through to advance biodegradation which is usually accomplished by native microorganisms. The debasement efficiency is enhanced by controlling parameters such as dampness content, pH, air circulation, temperature, and carbon-to-nitrogen proportion. This method is most effective in hydrocarbon-rich contaminant soils. Furthermore, the vigorous microbial movement debases the oil-based constituents adsorbed to soil particles, thereby subsequently reducing the groupings of these foreign substances. Target toxins, like gas, stream fuel, diesel fuel, and other petrol-derived items are taken out from the dirt by biodegradation and volatilization in the biopile. In this review, a thorough discussion is made on the different types of soils subjected to biopile treatment and the influence of several factors such as oxygen content, moisture content, pH, temperature, and nutrients on the efficiency of the biopile remediation technique. A comprehensive comparison is also drawn between the several types of bioremediation techniques such as landfarming, bioventing, phytoremediation, and composting to name a few. The cost-effectiveness of biopile treatment over other existing bioremediation techniques is also addressed.

In the present study, the cost and environmental benefits attainable with the usage of flyash (FA) in earthworks are evaluated through cost analysis (CA) and carbon footprint analysis (CFA). A current public project involving highway embankment construction was considered for the CA and CFA on FA utilization. The geotechnical evaluation is followed by CA and CFA to quantify the estimated costs and carbon emissions in the following two scenarios, i.e. (I) FA-based embankment and (II) pavement constructed with FA as sub-base material. The CFA and CA results were extended to understand the effect of stabilizers such as lime and cement on construction’s overall emissions and costs. The CFA results indicate that FA procurement (embodied) influences the amount of carbon emissions and the overall costs with a share of 78% and 61% in scenarios I and II, respectively. It is noted that the utilization of hydrated lime and portland cement as stabilizers could enhance the costs by 513 Re/m3and 722 Re/m3, respectively. Consequently, the results of the study validated the fact that the utilization of FA as an alternative to natural soils is a sustainable solution with a positive influence on the environment.

In the design protocols of pavement subgrade layers, the resilient modulus (MR) property assumes importance in evaluating the performance during their life-time under sustainable repeated or dynamics traffic-loads. The aim of this study is to evaluate the improvements achieved on the subgrade layers of fiber-treated lime-blended expansive soil. Two types of fibers exhibiting different surface properties were considered and their length(s) and dosage(s) (by dry weight of soil) were varied as 6 mm and 12 mm; and 0.2% and 0.6%, respectively. To ensure bonding between fiber and soil particles, dehydrated lime has been added to the soil-fiber mixture. The compacted specimens were cured up to 28 days. Dynamic resilient modulus MRtests were carried out in the laboratory for soil–lime-fiber mixtures using dynamic triaxial device. The obtained MRvalues were correlated with California Bearing Ratio (CBR) and Unconfined Compression Strength (UCS) values and appropriate models have been proposed to estimate MR. The results show significant increments in MRdue to fiber reinforcement and are affected by fiber type, length and dosage. The proposed models considering CBR and UCS to predict MRhave shown excellent correlations.

Global rise in greenhouse gas emissions (GHG) is triggered mainly due to the consumption of fossil fuels for power generation and domestic usage. Among the fossil fuels, coal is a primary contributor to global GHG with substantial emissions generated during its mining and combustion process. Coal gangue, a residue produced during the coal mining process, has found sparse utilization in civil engineering applications. To gauge the feasibility of using coal gangue for geotechnical and geoenvironmental applications, comprehensive characterization study was performed which include understanding the geotechnical, mineralogical, chemical and leaching behavior. Further, to evaluate the environmental impacts associated with coal gangue utilization, carbon footprint assessment (CFA) was performed. The geotechnical properties of coal gangue revealed its potential as fill material in the construction of embankments and retaining walls. Mineralogical and chemical characteristics of coal gangue are comparable to coal combustion residues like coal ash and fly ash which are widely used in bulk civil engineering applications. The leaching studies revealed the presence of trace elements in coal gangue; however, their concentration levels were found to be well below permissible limits. The CFA has shown that utilization of coal gangue in mechanically stabilized earth wall construction resulted in a net savings of 1709 CO2(kg) emissions. Based on the characterization studies, it can be inferred that coal gangue is a potential alternative to the existing conventional geomaterials like soils and other recycled materials.