•A copula based Bayesian approach for characterizing joint distribution from limited data is proposed.•Detailed formulation for the joint density of soil-water characteristic curve parameters is ...presented.•Non-normal truncated distribution and non-linear association are simultaneously considered.•The proposed approach performs well for low, medium as well as high suction range.•Site-specific unsaturated reliability based design can be conducted even with only a few soil-water characteristic curves.
Soil-water characteristic curve is an essential constitutive relationship required for modelling unsaturated soil behaviour. Earlier supposed to be characteristic or unique for a particular soil, it is now well established that there are various sources of uncertainty which lead to different curves for the same soil. Hence it becomes necessary to probabilistically characterize soil-water characteristic curve for the purpose of reliability based design in unsaturated geotechnical engineering projects. Popular approach is to parametrize the soil-water characteristic curves into a set of curve fitting parameters and evolve the joint distribution of these parameters. However, a satisfactory probabilistic characterization requires large number of realizations and is practically not feasible since experimental measurement of soil-water characteristic curve is an expensive, time intensive and difficult task. For all practical purposes, it is impossible to obtain a large number of curves to arrive at the site-specific probability distribution. Therefore, this study proposes a Bayesian approach integrated with copula theory to obtain the joint probability distribution of soil-water characteristic curve parameters from limited number of curves. Limited number of curves are incorporated with prior knowledge to obtain the updated probability distribution of soil-water characteristic curve parameters. Efficacy of the proposed approach is demonstrated on three databases, one each for loam, fly ash and bentonite. Finally for demonstrating a practical application of the proposed approach, a site specific reliability based design of unsaturated slope is conducted.
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Biochar produced from weed Eichhornia crassipes increases water retention and reduces surface cracks.
•Study investigates biochar (BC) from water hyacinth (WH) weed as soil ...amendment.•BC as soil amendment material is found to suppress crack and enhance water retention.•Gradual increase in water retention with WH BC addition.•Inclusion of biochar decreases the desiccation crack in soils.
Water hyacinth (WH), is one of the world's most intractable and invasive weed species. Recent studies explored the efficacy of this species as a biochar (BC) in improving soil fertility and metal adsorption. However, the soil water retention (SWR) property and crack potential of soil-WH biochar composite has still not been studied. The major objective of this study is to investigate the SWR property and corresponding crack intensity factor (CIF) for compacted soil-WH BC composites. Soil-WH BC composites at five percentages (0, 2, 5, 10 and 15) was compacted and soil parameters such as suction (ψ), water content and CIF were simultaneously monitored for 63 days (including 9 drying-wetting cycles). Results showed that soil-WH BC composite at all percentages retains more water (max. 19% and min. 6.53%) than bare soil at both saturated and drought conditions. Gradual inclusion of WH BC to soil decreases the CIF potential from 7% to 2.8%.
Meticulous research has been done to observe and measure the impact of biochar on soil-water retention properties. On the contrary, very little research is conducted on quantifying cracking in soil ...biochar composites. Investigation of crack intensity factor is essential as it affects permeability and hence, overall water balance in agricultural fields. It is well known that cracking of soil is influenced by suction and water content but their interactive effects are not very well understood. This technical note aims to investigate the cracking of soil amended with biochar made out of water hyacinth, an invasive weed, with focus on analysing interactive effects of water content and soil suction. An integrated reduced scale monitoring and modelling using artificial neural networks have been adopted. A series of tests were conducted to monitor suction, water content and crack intensity factor in soils mixed with four different compositions i.e. 0%, 2%, 5% and 10% by weight of biochar for around 3 months. The measured results have been evaluated first, and eventually modelled using artificial neural networks to predict crack intensity factor as function of water content and suction for all composites. In most of the cases it has been found that suction is more influential than water content. However, the relative significance of suction to water content in determining crack intensity factor decreases with increase in biochar content of soil. It is concluded that the optimum biochar content is 10% for most of the agricultural purposes based on the water retention capacity and cracking. The probability distribution of crack intensity factor is found to be normal for case with 5% biochar and while for others, it is skewed negatively. A simple cost based analysis taking in context of a small developing urban city of India, showcased a cost savings in irrigation of urban infrastructure by around 63,000 US dollars for a particular summer.
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Thermal characteristics such as thermal conductivity and specific volume heat capacity are the significantly important parameters for the backfill materials for underground power cable. Herein, the ...thermal characteristics of fly ash (fluidizer), bentonite, and their mixes (fly ash content: 20%, 40%, 50%, and 70% by mass) were measured using a KD2 Pro thermal probe, and the effect of fly ash content and volumetric water content were studied. The experimental results indicate that the thermal conductivity and specific volume heat capacity increased with increase in the fly ash content and the volumetric water content. Further, a correlation between thermal conductivity versus volumetric air content and fly ash has been established based on experimental results. The established correlation was verified with the data obtained from the present study as well as from the data available in existing works of the literature. The proposed calculation model estimated the thermal conductivity with relative error of 8.53–16.40% of bentonite and bentonite–fly ash mixture. The predicted result showed that the established correlation will be useful to predict the thermal conductivity of bentonite–fly ash or similar soil and soil mixtures. The experimental outcomes can be widely applicable for thermal backfill applications for underground power cable systems.
The surrounding (backfill) materials around the underground power cable systems are essential for dissipating the heat away from it, during the exertion phases. The heat dissipation restrains the ...thermal instability and risk of progressive drying of the backfill materials, thus reducing the thermal stress on the power cable. Thermal instability indicates the reduction in thermal properties (conductivity or diffusivity) due to the migration of moisture because of heat accumulation. Thus, the backfill materials should have adequate thermal properties and water retention capacity to transfer the heat from the heat source to the surrounding area with minimal moisture migration. The bentonite has high water retention capacity, but low thermal conductivity, whereas sand/fly ash exhibits low water retention and has higher thermal conductivity than bentonite. The addition of bentonite promotes the water holding capacity and thermophysical properties of sand and fly ash. Therefore, this study presents the thermal properties of backfill materials, bentonite–fly ash (B–F) and bentonite–sand (B–S), at varying weight-percent of sand and fly ash with bentonite. Various compositions of the mixtures were compacted to varying dry densities, and water contents and thermal properties variation of backfill materials were measured using a dual thermal needle probe ‘KD2 Pro’ at room temperature. The study deals with the systematic evaluation of the volumetric specific heat capacity, thermal conductivity, and diffusivity of backfill materials against varying dry density and water content. The threshold water content (TWC) has been determined from the thermal diffusivity–water content variation curve, and it has correlated with plastic limit (PL) and optimum moisture content (OMC). Thereafter, the efficacies of two thermal conductivity prediction models have also been evaluated statistically with respect to experimental results.
Biochar amended soil (BAS) has been explored as a cover material for geo-environmental applications such as landfill cover due to its vegetation potential. Soil erosion in these infrastructures can ...progressively lead to failure and hamper the workability of the system. BAS is compacted for geo-environmental applications, unlike agricultural soil, which are loose in nature. Furthermore, the love-hate relationship of biochar with water can potentially affect the functioning of compacted cover system. Thus, the performance of compacted BAS in the context of erosion potential is not well understood. The major objective of this technical note was to explore the erosion potential of compacted BAS sourced from four distinct biochars. Biochar were produced in-house and mixed with soil at 5% and 10% by weight. In total, 81 pinhole erosion tests were performed to gauge the erosion rate of bare soil and BAS at three different compaction states at same compaction energy. It was revealed that the erosion rate decreased with gradual increment in water content for BAS, which was mainly attributed to the change of particle orientation from flocculated to dispersed along the compaction curve. Addition of biochar to soil resulted in decrease of erosion along the dry state whereas the opposite was observed for wet state. This was attributed to the surface functional groups as well as particle gradation of biochar. Erodibility coefficient and critical shear stress plot of soil and BAS revealed that addition of biochar had minimal effect on erosion of compacted silty sand.
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•Production of biochar from different wastes for compacted soil erosion treatment•Surface functional groups and particle morphology of biochar influence soil erosion•Addition of biochar had minimal effect on erosion of compacted silty sand.
AbstractThermal backfill is essential for projects such as underground crude oil pipelines and crude oil storage tanks to control the heat migration from the source. The properties of locally ...available soil may not be adequate as thermal backfill and hence need suitable amendment. Biochar is a low thermal conductive material and may contribute to an increase in soil strength. There are no such studies that deal with the thermal properties of biochar-based backfill. Further, the influence of biochar particle size fractions on soil thermal properties has not been reported until now. Therefore, the possibility of biochar as a soil amendment for modifying thermal backfill characteristics is explored in this study. Two types of soils (highly plastic silt and clayey sand) are amended with three biochar content amounts (5%, 10%, and 15%), and three different particle size fractions coarse (4.7–2 mm), medium (2–0.425 mm), and fine (0.425–0.075 mm), and their compaction characteristics as well as thermal and mechanical properties are investigated. It was observed that the amendment of biochar in soil reduced the thermal and mechanical properties of the soil. Further, the reduction in soil thermal conductivity and volumetric heat capacity with biochar amendment was more in coarser biochar fraction than finer and medium fractions. In comparison, reduction in unconfined compressive strength (UCS) was more in finer biochar fraction. Additionally, the thermal properties reduction was higher in clayey sand than highly plastic silt. An inverse linear correlation of thermal conductivity with pH and electrical conductivity were observed for both soil biochar mixes. The relationship between the thermal properties and UCS indicates that the medium fraction biochar provides the optimized value for reducing thermal properties and UCS of biochar amended soil (BAS). This proves the efficacy of BAS as thermal backfill.
With rapid advancements in technology globally, the use of plastics such as polyethylene bags, bottles etc. is also increasing. The disposal of thrown away wastes pose a serious challenge since most ...of the plastic wastes are non-biodegradable and unfit for incineration as they emit harmful gases. Soil stabilization improves the engineering properties of weak soils by controlled compaction or adding stabilizers like cement, lime etc. but these additives also have become expensive in recent years. This paper presents a detailed study on the behavior and use of waste plastic in soil improvement. Experimental investigation on reinforced plastic soil results showed that, plastic can be used as an effective stabilizer so as to encounter waste disposal problem as well as an economical solution for stabilizing weak soils. Plastic reinforced soil behaves like a fiber reinforced soil. This study involves the investigation of the effect of plastic bottle strips on silty sand for which a series of compaction, direct shear and California bearing ratio (CBR) tests have been performed with varying percentages of plastic strips and also with different aspect ratios in terms of size. The results reflect that there is significant increment in maximum dry unit weight, Shear Strength Parameters and CBR value with plastic reinforcement in soil. The quantum of improvement in the soil properties depends on type of soil, plastic content and size of strip. It is observed from the study that, improvement in engineering properties of silty sand is achieved at 0.4% plastic content with strip size of (15 mm × 15 mm).
Purpose
The purpose of this study is to measure the effects of density, moisture, fiber content on unconfined compressive strength (UCS) of soil by formulating the models based on evolutionary ...approach and artificial neural networks (ANN).
Design/methodology/approach
The present work proposes evolutionary approach of multi-gene genetic programming (MGGP) to formulate the functional relationships between UCS of reinforced soil and four inputs (soil moisture, soil density, fiber content and unreinforced soil strength) of the silty sand. The hidden non-linear relationships between UCS of reinforced soil and the four inputs are determined by sensitivity and parametric analysis of the MGGP model.
Findings
The performance of MGGP is compared to those of ANN and the statistical analysis indicates that the MGGP model is the best and is able to generalize the UCS of reinforced soil satisfactorily beyond the given input range.
Research limitations/implications
The explicit MGGP model will be useful to provide optimum input values for design and analysis of various geotechnical infrastructures. In addition, utilization of Water hyacinth reinforced fiber reinforced soil will minimize negative impact of this species on environment and may generate rural employment.
Originality/value
This work is first of its kind in application and development of explicit holistic model for evaluating the compressive strength of heterogeneous soil blinded with fiber content. This includes the experimental and cross-validation for testing robustness of the model.
•Retention of heavy metal copper in fly ash under multiple ions.•Limitations in analytical solution for predicting retention under multiple ions.•Retardation factor from Freundlich isotherm predicts ...more than Langmuir.•Freundlich isotherm is recommended modelling transport of copper ions.
Many previous studies of soil contaminant treatment have primarily analysed heavy metal contaminant ion retention in fly ash (FA) in a single isolated medium whereas, factoring out the competitive systems. This study seeks to determine the interaction of the heavy metal copper ion (Cu+2) with fly ash under single and competitive systems and also to expound its impact on fate prediction. Freundlich and Langmuir non-linear isotherms were adopted to quantify the sorption results. The retardation factor attained from Freundlich isotherm predicts more than Langmuir. The Langmuir isotherm break-through-curves (BTC) was slightly earlier in break through, with a sharp front and prolonged tailing, whereas the Freundlich isotherm appears considerably after the production of a spreading pollutant front. Freundlich retardation factors established in this study was employed to one-dimensional (1-D) solute transport model, which successfully stimulated good prediction for sorption by fly ash. Conversely, significant inconsistencies were identified from the Langmuir isotherm for evaluating the fate of Cu+2 at high concentration range. This study recommends Freundlich isotherm for modelling transport of copper ions in a competitive environment in fly ash.
