The application of biochar in agricultural practices and vegetative slopes has been rigorously recommended in previous literature. However, its potential application in other industries is scarcely ...explored. Biochar is a chemically stable material with a low thermal conductivity, which makes it a perfect fit for blending with soil to use as thermal backfills. A thermal backfill is an essential component for maintaining the ambient temperature around the underground pipelines and storage tanks of crude oil industries. This study investigates the potential application of eighteen soil-biochar blends as thermal backfill. Highly plastic silt and clayey sand (SC) soil were amended with three different biochar types viz. hardwood biochar, water hyacinth biochar, and sugarcane bagasse biochar (SBBC), at three biochar contents of 2.5%, 5%, 7.5% (w/w). Thereafter, their compaction characteristics, thermal and physicochemical properties were investigated. The thermal conductivity (
K
) and volumetric heat capacity (
C
) of MH soil were reduced by 22%, 29%, 33%, and 16%, 24%, 26% with 7.5% amendment of hardwood, water hyacinth, and SBBC. Similarly,
K
and
C
values of SC soil decreased by 22%, 34%, 37%, and l2%, 18%, and 20%. The micrographic analysis of soil-biochar blend reveals that the entrapped air in biochar particles governs the heat transfer in biochar-amended soil. An inverse correlation of thermal conductivity with pH and electrical conductivity was also observed for the soil-biochar mixes. This study extends the domain of biochar application highlighting the engineering properties of different blends, which would be helpful for its field-scale application.
Graphical Abstract
Purpose
Ammonium and potassium are nutrients that generally co-exist together in soils in municipal wasteland. The main objective of this study is to investigate the interactive effects of NH
4
+
and ...K
+
on their sorption characteristics in seven different soils.
Materials and methods
The adsorption parameters (Freundlich partition coefficient
K
F
and maximum contaminant adsorbed by solid
Q
m
) of both the isotherms for single and competitive interactions were correlated with soil-specific parameters (total specific surface area (SSA) and cation exchange capacity (CEC)). To depict the significant variation of the ions in the presence of other ions, percentage reduction of the isotherm parameters was calculated.
Results and discussion
Both the ions exhibited a competitive mode of inhibition in the presence of one another. However, the effects varied with soils and the range of concentration. The study demonstrated that at lower concentration, the NH
4
+
and K
+
ion competed equally in all the soils. However, after a certain range of concentration unique for each soil, NH
4
+
retention was found to be marginally higher than K
+
. The study also signified some analogous values of the Freundlich and Langmuir isotherm parameters for soils like F Bent and Kao, which contradicted other experimental findings.
Conclusions
This study can be useful for predicting fate of potassium and ammonium for risk assessment of contaminated sites and hence, in design or analysis of certain waste contaminant barrier under concept of sponge city.
Few studies numerically investigated evaporation through cracked soil using macro pore size distribution approach (conventional approach). In previous studies, the experimental results used for the ...simulation were usually obtained by evaporation from a very small mould. Moreover, those results are prone to size and boundary effects and can influence simulated soil moisture distribution around crack. In addition, difference between volumetric water contents (VWCs) computed using conventional approach and measured VWCs is relatively high. The main objective of the present study is to propose a new approach for simulating evaporation through cracked soil. The new approach draws analogy from root water uptake model, which includes a sink term. For validation, a large-scale experimental setup was designed and developed to obtain the experimental results by minimizing boundary effects. The experimental setup was instrumented to measure suction and VWC. Commercial finite element package “HYDRUS” was used to numerically solve (simulate) the Richards equation coupled with sink term. This study revealed that, root water uptake approach is appropriate for simulation of large reduction in VWCs under evaporation. Maximum difference between computed VWCs using conventional method and measured VWCs was observed to be 21%. Whereas, maximum difference between VWCs computed using novel root water uptake approach and measured VWCs was observed to be 16%. The proposed approach was able to predict soil moisture distributions more reasonably as it allows loss of water through cracks on soil surface.
AbstractThis study demonstrates the importance of selecting an appropriate liquid-to-solid ratio (L∶S) for batch sorption study (BSS) of bentonite (BE). The current recommended L∶S is 20 for BSS of ...soils and sediments, which works well for most of the soils/sediments. However, for expansive soil like BE, L∶S=20 was found to be inadequate due to the formation of thick gel like consistency preventing proper interaction of metal ion with solid surface. This resulted in considerable underestimation of sorption capacity of BE. Effort was made to identify appropriate L∶S for BE for which there is no specific guideline available in the literature. Under controlled pH condition and Pb2+ as the model heavy metal ion, it was noted that the sorption capacity of BE increases with L∶S beyond 20 and with an increase in initial metal ion concentration. The highest percentage removal of Pb2+ was observed at L∶S=50 and lowest at L∶S=100 for initial concentration greater than 300 mg/L. The minimum L∶S possible for BE is 20, below which the interaction between the solution and soil solids becomes difficult due to formation of a thick gel like consistency. The interaction of BE with Pb2+ was further investigated from the results of field emission scanning electron microscopy (FESEM) integrated with energy dispersive X-ray spectroscopy (EDX). Fourier transform infrared (FTIR) spectrometer was used to identify the variations in interaction between the Pb2+ ions and functional group present on BE for various L∶S. It was concluded that for all practical purposes, L∶S=50 is a suitable ratio for determining sorption capacity of expansive soil like BE.
Growing awareness of sustainability in the landfill cover system has increased the use of biochar amendment for degraded landfill surface soils. Hydraulic and vegetative benefits of biochar on cover ...soil have been studied in the past, while ignoring mechanical characteristics, which is important to understand progressive failure of landfill infrastructure. In this study, the mechanical characteristics of four soil–biochar composites were investigated by conducting 81 unconfined compressive strength test. The results based on four in-house produced biochar were used to study the effect of compaction state (density, moisture content) and biochar percentage (5% and 10%) on unconfined compressive strength of soil–biochar. The ductility of soil–biochar was investigated for all the four biochars. Results from this study indicate a contrasting observation of strength gain depending on the type of biochar. The unconfined compressive strength of soil–biochar is potentially influenced by the different surface functional groups of biochar (hydrophilicity/hydrophobicity) and soil-biochar interlocking. It was noted that the peanut shell biochar gave comparable unconfined compressive strength of soil–biochar with that of bare soil for different compaction state. However, a diminution in the unconfined compressive strength was observed for all the other three soil–biochar sourced from water hyacinth, saw dust, and poultry litter. The study indicates that the use of biochar in soils does not ensure an improvement in the strength of soil–biochar. Enhancement in ductility was found for all the four soil–biochar irrespective of compaction state. Improvement in ductility was maximum when the soil–biochar is compacted at the dry state of optimum. Plant-based biochar has higher potency to increase the ductility of soil as compared to the animal-based biochar. Our study identifies peanut shell biochar ideal for landfill cover amendment material, considering its mechanical characteristics and design criterion. Soil biochar composite from water hyacinth, saw dust, and poultry litter can be used for potential application in green-infrastructure.
AbstractThis paper presents a comprehensive framework to understand the uncertainties associated with the water retention characteristic curve (WRCC) of fly ash, which is necessary for studying the ...unsaturated behavior of the fly ash. The measuring devices, range of measured suction, and water content play important roles in inducing the uncertainties associated with WRCC. To account for these uncertainties, a univariate probabilistic modeling was first adopted. Measured suction and volumetric water content were modeled as univariate random variables, the parameters of which were determined using quantile-quantile plots alongside the estimations of the best-fit probability distribution. To handle a wide range of uncertainties associated with WRCC zones and their measurements, the measured data were partitioned according to (1) saturation, desaturation, and residual zones and (2) the measurement range of four instruments. The bivariate dependencies were incorporated using a copula-based modeling and simulation approach wherein the marginals were chosen from the results of the univariate modeling. Results show that the univariate modeling provided a good firsthand estimate of the uncertainties of WRCCs, and when integrated with bivariate modeling and simulation, can yield representative WRCCs under considerably restricted measurement options. The study demonstrates the usefulness of copula-based probabilistic modeling for determining a realistic WRCC of fly ash under limited measured data availability.
Modeling the behavior of unsaturated soils necessitates the measurement of soil suction and the establishment of its variation with the water content, which is commonly known as the soil-water ...characteristic curve (SWCC). Several methodologies have been developed for measuring either total suction ψ (sum of matric suction ψm and osmotic suction ψo) or ψm. While employing different methodologies for suction measurement, there is a possibility that various factors (viz., type of the soil, measurement methodology, range of the suction measurement, equilibration time, and presence of salts or contaminants in the soil) may influence the results and hence the SWCC. Therefore, it is essential to investigate the uniqueness of SWCC, determined by using some commonly adopted suction measurement methodologies. This study indicates that the SWCC established by adopting different methodologies may not be unique and is primarily influenced by the range of suction measurement. As such, it is essential to highlight the range of suction values involved for establishing the SWCC, to facilitate unambiguous modeling and to precisely understand the behavior of unsaturated soil.
AbstractTo prevent fly ash from becoming an environmental hazard, it is very often used as a fill material in the construction of embankments. The stability of slopes incorporating the unsaturated ...behavior is of primary concern in these structures. This necessitates estimating the water retention characteristic curve (WRCC) of fly ash. However, the literature notes various uncertainties associated with the measurement of WRCC, mostly attributed to the inadequacy of instruments to measure wide range of suction. This paper investigates the impact of measurement uncertainties in WRCC on the reliability analysis of fly ash slope. The study shows a significant impact of uncertainties in WRCC on determining slope reliability. To quantify these uncertainties, a probabilistic model for WRCC is developed using the Gaussian copula and is incorporated into an unsaturated slope stability framework using Monte Carlo simulation. The study also shows the impact of the degree of correlation among WRCC parameters on the reliability analysis of slopes.
•Problem of Assessment of soil-fiber composite is undertaken in this work.•The effect of fiber content, moisture content and soil density on composite is studied.•Genetic programming with variable ...subtrees and depth is proposed to solve problem.•Parametric-Sensitivity analysis reveals complex relationships among the variables.•GP is able to estimate the mechanical factor of soil-fiber composite accurately.
Unconfined compressive strength (UCS) of soil is one of the basic index parameters for representing the compressive bearing strength of soil. Fiber reinforced soil is one of the most popular and practical ground improvement approaches used in geotechnical infrastructures. Analytical models for estimating UCS of soil-fiber composites have been developed in the literature. However, these models rarely incorporate the combined effects of dynamic field parameters such as fiber content, soil moisture, and density. These effects can be studied by the development of a holistic model based on a dimensionless strength improvement factor (SIF), which is defined as the ratio of UCS of reinforced soil to the unreinforced UCS. The current model estimating SIF indicates the improvement expected in UCS of soil-PP fiber composite based on the three design conditions such as fiber content, soil density, and moisture content. For this purpose, a series of 108 laboratory tests were first conducted to measure UCS of both fiber-reinforced soil and unreinforced soil under different fiber contents, soil density, and soil moisture content. Clayey silt soil and commercially used polypropylene (PP) fibers were selected in this study as soil and fiber material respectively. Genetic programming (GP) approach was then used to formulate models based on the measured data. The hidden non-linear relationships between SIF and the three inputs were determined by sensitivity and parametric analysis of the GP model. It was found that the moisture content in the soil has the highest influence on the strength factor that accounts for the change in strength. Coupled effects of soil parameters (soil moisture, soil density) and fiber content have been studied using parametric analysis which includes different possible field conditions (parameters). The results have been discussed along with the reinforcement mechanism of PP fiber for different soil conditions. It is believed that the robust GP model developed will be useful to determine optimum input values for designing safe bearing foundation soils which are reinforced with PP fibers.
Inorganic macro cations (Na
+
, K
+
and Ca
+
) co-exist in agricultural and municipal landfill sites. The retention behavior of these ions in different soils and combinations (binary and ternary ...system) has not been fully understood by previous studies. This study seeks to probe into the retention behavior of macro cations (Na
+
, K
+
, Ca
+2
) in six different soils under multiple combinations of ions solution. The retention of common ions was quantified by using Freundlich and Langmuir isotherms. Na
+
(single) pollutant-soil interaction was desorbed in most of the soils. The retention of K
+
and Ca
+2
was much greater than that of Na
+
. There is no definite trend for retention of Na
+
in the presence of K
+
. For all soils, the retention results of K
+
in the presence of Na
+
decreased. Affinity for K
+
was greater than that for Ca
+2
in most of the soils. This study also demonstrated the affinity sequence of the ion retention for each soil and the percentage reduction of ions in competition with respect to single ions. Anomalous trends of the isotherm parameter fitting suggested the limitation of the mathematical models in predicting the experimental data. These results can be helpful in improving accuracy of fate prediction of pollutant fate and thus, design of waste containment facilities for various wastes that contains inorganic ions.
