Soil Bed Research Articles

Utilization of Shredded Waste Tire as a Substitute for Gravel in Stone Column Groups

The present study investigates the load-carrying capacity response of gravel-shredded tire stone column groups as a strategy for strength improvement in loose soils. The experimental study was conducted using large-scale oedometer tests on the stone column groups of gravel and gravel-shredded tire mixtures of different tire content, arrays, and spacings. Also, the efficacy of shredded tire addition on the stone column group bearing behavior was explored using the unit cell concept. To this aim, the entire area of the unit cell was loaded to determine the stiffness of the improved bed soil while applying load directly on single stone columns was done to evaluate the load-carrying capacity of the reinforcing elements. The results demonstrate enhancements in the load-settlement behavior of the stone column groups in mixtures containing 20% of the shredded tire, while further tire addition can adversely affect it. Additionally, adding an optimum shredded tire to the stone column materials leads to an increase in stiffness (Young's Modulus) of the bed soil. This behavior is directly correlated with the created friction angle and area ratio (A/AS) of different arrangements of the stone column groups.

Suction effects during uplift of steel pipes buried in compacted soil

This paper presents an experimental study on quantifying the effects of soil suction on the resistance offered by compacted unsaturated backfills to uplift of buried steel pipes and identifying the mechanisms that contribute to increased resistance compared to similar pipes buried in dry sand. This is achieved by means of 1-g physical model experiments, with the pipe buried in sandy loam–Kaolin soil beds of varying water content (suction), compacted to the same dry unit weight. The main experiments are supplemented by benchmarking experiments performed in dry sand of similar grain size distribution, as well as in compacted soil beds inundated with water to achieve conditions close to full saturation. The experiments are supported by a detailed characterisation study of compacted sandy loam–Kaolin mixtures and mini-CPT tests performed to evaluate the uniformity of the soil beds. Measurements of the reaction developing on the pipe as function of its uplift displacement are co-evaluated together with images of the failure mechanisms obtained using particle image velocimetry and continuous measurements of soil matrix suction. We conclude with a simplified method to predict the peak reaction to pipe uplift that allows considering the contribution of suction and the tensile–shear failure mechanism observed during the experiments.

NUMERICAL STRENGTH CALCULATIONS OF UNDERGROUND GAS PIPELINES IN UNDERMINING AREAS

Introduction . Various calculation methods, including empirical, analytical, and numerical ones, are used to assess the effect of undermining on base deformations and force variations in the structures of existing and projected pipelines. Empirical methods are typically developed using an experimental analysis of numerous results obtained during the engineering and geodetic observations of settlements and surface terrain shifts in undermining areas. However, such methods fail to take into account all the factors affecting settlements and shifts during underground excavations, including the vertical heterogeneity and physicomechanical properties of soils, etc. Aim . To determine the advantages of numerical methods and to develop a methodology for using numerical calculations in the Plaxis and Midas GTS NX geotechnical software applications. Compared to empirical and analytical methods, numerical approaches have the advantage of simulating the bedding heterogeneity of geological engineering elements and their physicomechanical properties, ensuring joint calculations of the “underground excavation – soil massif – existing structure” system, considering the gradual character and undermining technology, as well as providing the possibility to search through a large quantity of variants over a short period of time. The principles of numerical calculations of the strength of underground main gas pipelines during the arrangement of closed underground excavations for mineral mining are considered. Methods . The developed methodology is based on the degree and nature of effects produced by various factors on numerical modeling results, including the presence of a pipeline in the design model, width of the model calculated area, finite element mesh sizes, parameters of the soil geomechanical model, width, bedding depth, dip angle, thickness, and number of mineral mined formations, as well as the problem statement type (2D or 3D). Results . The results of the study are presented in the form of a methodological verification, performed on the basis of a comparison between the calculated and actual parameters of rock shifts. Conclusions . The presented methodology reliably predicts base deformations and force variations in the structures of existing and projected pipelines during the excavation of a coal seam at one of the mines of the Moscow lignite basin.

Development of DEM-MBD coupling model for draft force prediction of agricultural tractor with plowing depth

During agricultural tillage, draft force is the most important factor affecting the performance of soil-machine system. In this study, a full-scale soil-tool-machine coupling model based on the coupling of DEM (discrete element method) and MBD (multibody dynamics) was established to predict draft force according to tillage depth during tillage operation. First, plowing field test was performed through a field load measurement system to develop DEM-MBD coupling model for the draft force prediction according to the tillage depth during the calibration and validation process of the DEM-MBD coupling model. The DEM soil bed was modeled by considering the target tillage depth and reflecting the soil property distribution that changes according to the soil depth. For the soil model, particle mass and surface energy were calibrated using bulk density values measured in the field and shear vane test results. In addition, the weight distribution ratio of each wheel in static state was measured, and the center of gravity was calculated for MBD modeling of the tractor-implement system. Additionally, calibration of tire parameters was performed using the travel speed results of field tests. As a result of the DEM-MBD coupled simulation, the prediction accuracy of travel speed and draft force were 93.2% (86.6%–99.4) and 90.8% (86.4%–99.3%), respectively, depending on the tillage depth. In addition, the prediction accuracy of the draft force was 11–32% higher than the 67.4–70.6% using the ASABE standard D497.4 method. This study is considered to be able to gradually replace the existing field tests with digital twin-based simulation tests. This can provide valuable insights for optimal design while minimizing the development time and cost of soil-machine systems.

Long-term response planting method on wheat under conservation agriculture

Objective: To compare different bed planting systems: narrow beds (80 cm), wide beds (100 cm), and flat soil, on the growth and yield of wheat under conservation system.
 Design/methodology/approach: Treatments were established on a complete block design with three replicates; also, wheat crop was grown during five seasons. Treatments were as follow: A) wide beds (furrows at 100 cm), B) narrow beds (furrows at 80 cm) and C) flat soil. Response variables were dry weight of 50 stems, weight of 1000 grains, number of spikes (m2), harvest index and yield. Also, the relationship between relative yield and cold units and degree-days were measured.
 Results: Flat soil reach the highest dry weight of 50 stems, whereas narrow beds had the maximum number of spikes per m2. Yield was equal between flat soil and narrow beds. No differences were found in the harvest index (HI) among the evaluated treatments. When comparing results between years, dry weight of 50 stems increased and the HI index decreased, affecting negatively the yield. A negative association was found between chill hours and yield.
 Findings/conclusions: Despite yield was equal between flat soil and narrow beds, reduction on yields was mainly associated with of reduction in chill hours occurring in each season.

Impact of cover crop and mulching on soil physical properties and soil nutrients in a citrus orchard.

BackgroundCover crops and mulching can ameliorate soil porosity and nutrient availability, but their effects on the physical characteristics and nutrients in the raised bed soils are unclear.MethodsThe field experiment was conducted in a pomelo orchard from 2019 to 2021, with an area of 1,500 m2. The treatments included control (no cover crop), non-legume cover crop (Commelina communis L.), legume cover crop (Arachis pintoi Krabov & W.C. Gregory), and rice straw mulching (Oryza sativa L.). At the end of each year (2019, 2020, and 2021), soil samples were collected at four different layers (0–10, 10–20, 20–30, and 30–40 cm) in each treatment. Soil bulk density, soil porosity, and the concentration of nutrients in the soil were investigated.ResultsThe results revealed that soil bulk density at two depths, 0–10 and 10–20 cm, was reduced by 0.07 and 0.08 g cm−3 by rice straw mulch and a leguminous cover crop, thus, increasing soil porosity by ~2.74% and ~3.01%, respectively. Soil nutrients (Ca, K, Fe, and Zn) at topsoil (0–10 cm) and subsoil (10–20 cm) layers were not significantly different in the first year, but those nutrients (Ca, K, Fe, and Zn) improved greatly in the second and third years.ConclusionsLegume cover crops and straw mulch enhanced soil porosity and plant nutrient availability (Ca, K, Fe, and Zn). These conservation practices best benefit fruit orchards cultivated in the raised bed soils.

A novel irrigation canal scheduling model adaptable to the spatial-temporal variability of water conveyance loss

The water conveyance loss of irrigation canals shows significant spatial-temporal variability both along the canal reach and over time. An accurate representation of these variances in irrigation canal scheduling is essential to reduce water conveyance loss. However, the existing optimal irrigation scheduling models (OISMs) still have deficiencies in dealing with spatial-temporal variability of water conveyance losses, which seriously limits the model performance in many irrigation areas with high spatial-temporal variability. Borrowing a concept from hydrology, we propose a Dynamic Calculation Method of canal water conveyance loss (DMWCL), in which antecedent water conveyance index (AWCI) is defined to represent the effects of antecedent soil water content upon infiltration losses, and the integral-flow balance method is adopted to describe the characteristics of canal discharge decreasing along the canal reach. Based on the DMWCL, we present a novel canal scheduling model with the potential to adapt to spatial-temporal variability (DMWCL-CS). The new model is applied to the Hetao Irrigation District, Inner Mongolia, a typical agricultural watershed in China. Our results across the case studies show that the canal water delivery schedule derived by the DMWCL-CS model reduces water conveyance loss and improves irrigation performance, ranging from 2.49 million m3 to 10.60 million m3 in 2014 and from 0.60 million m3 to 6.17 million m3 in 2016, respectively, compared to that of three additional models. Interestingly, we find that the water delivery schedule of the DMWCL-CS model accelerates the wetting process of the canal bed soil to reduce the water conveyance loss and increases the discharge to adapt to the characteristics that the discharge decreases along the canal reach. The DMWCL-CS model provides essential insights for irrigation managers to formulate a canal water delivery schedule that adapts to spatial-temporal variability. The proposed framework is generic and can be integrated into any OISM.

Calcium Lignosulfonate Can Mitigate the Impact of Salt Stress on Growth, Physiological, and Yield Characteristics of Two Barley Cultivars (Hordeum vulgare L.)

The current study was conducted in a pot experiment with sand bed soil for two winter seasons (2019/20, 2020/21) to illuminate the impact of calcium lignosulfonate (Ca-LIGN) (100 mg/L) in alleviating various levels of NaCl (0, 100, 200, and 300 mM) on two barley cultivars, Giza132 and Giza133. Giza133 outgrew Giza132 under salinity stress by accumulating less Na+ content and retaining more K+ content. Surprisingly, Ca-LIGN was shown to be involved in both cultivars’ capacity to efflux Na+ in return for greater K+ influx under 100 and 200 mM NaCl, resulting in an increased dry weight of shoots and roots as well as leaf area compared with the untreated salinity levels. Physiological parameters were measured as relative water content (RWC), electrolyte leakage rate (ELR), peroxidase activity (POD) in leaf and root and grain yield, and grain protein content were evaluated. Adding Ca-LIGN ameliorated both cultivars’ growth in all the recorded characteristics. Under salinity stress, Ca-LIGN induced a higher RWC in both cultivars compared to those without Ca-LIGN. Although the ELR increased significantly in Giza132 leaves under the different NaCl concentrations compared to in Giza133 leaves, applying Ca-LIGN for both cultivars reduced the deterioration in their leaf and root by significantly lowering the ELR. As a result, applying Ca-LIGN to the salinity-affected plants (Giza133 and Giza132) under (100 and 200 mM NaCl), respectively, inhibited POD activity by about (10-fold, 6-fold, and 3-fold, 5-fold). The impact of Ca-LIGN on grain yield was more effective in Giza133 than in Giza132, with (61.46, 35.04, 29.21% and 46.02, 24.16, 21.96%) at various salinity levels. Moreover, while both cultivars recorded similar protein content under normal conditions, adding Ca-LIGN increased protein accumulation by raising salinity concentration until it reached 3% and 2% increases in both cultivars, Giza133 and Giza132, respectively, under 300 mM NaCl. It can be concluded that applying Ca-LIGN on barley can help to alleviate the ionic stress by excluding the harmful ions, resulting in higher grain yield and protein content.

Free-field soil response to bidirectional horizontal non-uniform ground motion from multi-point shaking table tests

This paper assesses the dynamic nonlinear free-field soil response under bidirectional horizontal non-uniform excitation through a series of multi-point 1 g shaking table tests. The soil bed was enclosed in an innovative soil box supported by an array of three shake tables and was subjected to uniform and non-uniform ground motions in one and two horizontal directions. The soil response to bidirectional and unidirectional excitations, both uniform and non-uniform, were compared and discussed in terms of acceleration time history and Fourier spectra, acceleration amplification factor and soil settlement, as well as shear stress-shear strain behavior. The comparison of soil responses to bidirectional and unidirectional shakings demonstrated that the trends of peak acceleration amplification factors are similar along soil depth, but the response difference between bidirectional and unidirectional shaking is increasingly higher along the soil profile towards the ground surface, especially for uniform excitation. The variations of soil settlement, shear stress-strain and damping curves under bidirectional excitation were similar to that under longitudinal excitation; however, they were much different than those observed under transverse excitation. The soil damping in Y-direction under non-uniform excitation was larger than that under uniform excitation. These different site response characteristics under bidirectional non-uniform excitation should be properly considered in the seismic design of extended infrastructure.

Three-dimensional reliability analysis of unsaturated soil slope considering permeability rotated anisotropy random fields

The spatial variability is an inherent characteristic of soils. In addition to isotropic and transversely anisotropic soils, rotated anisotropic soils can also be observed in nature owing to deposition and weathering. Recent studies revealed that the spatially variable soil strength parameters can significantly affect rotated anisotropically deposited soil slope stability. However, the influence of spatial variability of saturated water permeability (ks) on this type of slope stability has been not fully understood, especially for the three-dimensional (3D) slope analysis. This paper aims to investigate unsaturated soil slope reliability with 3D ks rotated anisotropy random fields under rainfall infiltration. Due to the low efficiency of the covariance matric decomposition method (CMD) in simulating large-scale 3D rotated anisotropy random fields, a modified CMD method is proposed to save the computational cost. Moreover, comparisons between 2D and 3D random finite element analyses are also discussed. The results indicate the modified CMD method can markedly improve computational efficiency by more than 3.3 times compared with the CMD method. Only applying variations of pore water pressure (PWP) of a section or groundwater table (GWT) cannot sufficiently account for the uncertainty of slope stability. The cross-dip slope, where the dip direction of the slope is perpendicular to the dip direction of strata, has a larger reliability index (1.3−3.0 times) than the dip slope and reverse slope at the same soil bedding plane orientation. The most unfavorable soil bedding plane orientation for the cross-dip slope and the dip/reverse slope is 0° (horizontally deposited) and 30° (slightly larger than slope angle), respectively. It is attributed to the relatively low ks along these two orientations being more likely to form the aquiclude, affecting overall variations of PWP, leading to a larger standard deviation of the factor of safety and a lower reliability index. Furthermore, the reliability of cross-dip slope can only be studied in 3D, while the dip slope and reverse slope reliability can be studied with 2D analysis to decrease computational burden when the slope length does not exceed 50 m.

Dry-air technology for stabilising weak deposits

Many available ground improvement techniques are effective, but involve large amounts of carbon dioxide emissions. Any green ground improvement technique would thus be beneficial. In this work, dry air, supplied at low pressure and relative humidity, was used to remove water from a soft soil deposit. The investigation was carried out at model scale, with a soft soil layer formed in a box of size 1.0 × 1.0 × 0.75 m. The soil bed was fitted with slender granular columns for the injection of dry air. The technique is the reverse process of vacuum consolidation, in which the magnitude of negative pore water pressure that can be applied to the soil is limited and thus requires careful construction procedures. The dry-air approach is simple and does not require any complex construction procedures. The investigations carried out over a limited period showed a significant improvement in the strength of the soil bed, indicating possible full-scale implementation. Full-scale implementation of the technique may not require any new construction methods as the procedure is very similar to that adopted in vacuum consolidation. However, variabilities in ground conditions, including the groundwater table, may pose additional challenges and supplementary information (soil–water characteristic data and numerical modelling) may be necessary to implement this technique at full scale.

Local Scour at Complex Bridge Piers in Bangladesh Rivers: Reflections from a Large Study

Many small-scale experimental, field, and empirical studies on bridge scour are available, however a large-scale study on local scour at a complex pier with wide variation in design parameters is still lacking. In this study, a country-wide assessment of local scour at complex piers of 239 bridges in Bangladesh is made. The hydrologic, hydraulic, and sediment data required in the assessment are obtained from secondary sources, primary measurements and samples, and numerical model simulations. An incredible number of 239 field visits are made, 1434 km of bathymetric surveys are carried out, and 478 samples of bed soils are collected and analyzed. The local scour depth is estimated using a complex pier configuration with pier, pile, and pile cap dimensions selected in consultation with structural and geotechnical engineers of bridge design. Flood frequency analysis and the HEC-RAS model simulation are used to estimate the hydrologic and hydrodynamic parameters needed in the assessment. A number of empirical formulations are used to estimate and compare the design local scours. The formulae of Melville and Coleman, Jain and Fischer, and Richardson are found to be dominant when deciding the design local scour depth at the bridge piers. Suggestions are provided to include a few additional equations in scour estimation and to develop a unified Bangladesh standard for scour depth estimation. The findings and recommendations of the study would be useful in planning and designing bridges in alluvial deltaic settings, particularly in the selection of empirical methods and mainstreaming of complex pier configuration in bridge scour assessment.

Numerical Modelling of the Effects of Liquefaction on the Upheaval Buckling of Offshore Pipelines Using the PM4Sand Model

The buckling tendency of an offshore pipeline buried in a liquefiable soil aggravates under earthquake situations. Moreover, to understand the upheaval displacement behavior of an offshore pipeline under dynamic loading, it is crucial to understand the variation of liquefaction potential within the soil bed. Thus, in the present study, the variation of the liquefaction potential within the soil body and its effect on the pipeline upheaval displacement (u) and post-shake uplift resistance (Vup) is investigated using a finite element package called PLAXIS 2D. The study was performed for different seismic and soil conditions. To define the soil, two advanced constitutive models are used. The static stages are modelled with the ‘Hardening Soil Model with small strain’ (HSS model), while the dynamic stage is modelled with the PM4Sand model. Moreover, the problem is defined as a 2d plane strain problem. The pipe is considered to be covered with Nevada sand. Several parameters such as a sand-density index (Dr), pipe embedment depth (H), seismic frequency (f) and amplitude are varied to study the variation of the soil liquefaction potential, the pipe upheaval buckling and the post-shake uplift resistance. The model is validated with past studies and a considerable match is obtained. The liquefaction potential is shown using the shadings of a user-defined parameter called a pore water pressure ratio (ru). Moreover, the variation of pipe upheaval displacement (u) and pipe uplift resistance (Vup) are shown using various plots. Thus, it is observed that the liquefaction potential is reduced with an increase in the frequency and the amplitude of the seismic signal. Moreover, the peak upheaval buckling, and the duration of earthquake loading to reach the peak upheaval buckling, decreased with an increase in the earthquake signal frequency. Again, the variation of post-peak uplift resistance of the buried pipeline with the pipe embedment depth is observed to be independent of the signal parameters. However, the variation of uplift resistance of the pipeline with the soil relative density is influenced by the signal parameters.

Design of an Innovative Tractor-Operated Seeder for Mat Type Paddy Nursery

This study contains the design approach, development details, and field evaluation of an innovative tractor-operated seeder for sowing mat type paddy nursery. In order to design and select the various components of mat type nursery seeder, the fundamentals of farm machinery design were taken into due consideration. The machine comprises of soil cutting unit, inclined conveyor unit, screw type conveyor auger, sieving unit, compaction roller, polythene sheet laying unit, soil metering and seed metering unit. The basic criteria for design were to prepare a soil bed with a width of 1000 mm and width of cut of channel 240 mm on both sides of the bed to irrigate the prepared soil bed. The soil cutting unit and conveyor unit were designed based upon amount of soil required on soil bed to have 20–30 mm soil mat bed thickness and seed metering unit was designed to deliver 2–3 seeds∙cm−2 on the bed. The machine was fabricated based on design calculations and then evaluated in laboratory as well as actual field conditions. During field evaluation of this machine, it was found that the coefficient of uniformity for seed spread was 7.33%, coefficient of uniformity for soil spread 5.67%, fuel consumption 39.6 l.ha−1 and actual field capacity 0.11 ha∙h−1 with 1.7 km∙h−1 forward speed of machine. Labour saving using the designed tractor-operated seeder was observed to be 86.4% as compared to the manual method of sowing mat type nursery using steel frames.

Load–Temperature Coupling Effect on the Base Plate End of the Whole Tram Road

Although trams have been widely recognized, systematic and comprehensive research on their design and construction is lacking. Based on the ABAQUS finite element software, we constructed a three-dimensional finite element analysis model of the overall track bed of the tram. Taking the most unfavorable working condition of load and temperature coupling as the research object, that is from 5:30 to 6:00 a.m., the load was applied to the plate end position. The simulation experiments were carried out by selecting different thicknesses of the track bed slab, support layer thickness, contact conditions between the track bed slab and the support layer, the modulus of the track bed slab, the modulus of the support layer and the soil foundation strength, and the stress and deflection of the subgrade were calculated. The most unfavorable load–temperature coupling condition was taken as the research object, that is, applying a load of 5.5–6 points on the plate end. Different track bed slab thicknesses, support layer thicknesses, contact conditions between track bed slab and support layer, track bed slab moduli, support layer moduli, and foundation strengths were utilized to conduct simulation tests for calculating the stress and deflection of the subgrade. Under the coupling effect of load on the end of the slab and the effect of temperature, changing the thickness of the track bed slab and the coefficient of friction between layers can improve the lateral force and deflection of the track bed slab. The effect of deflection is small. Changing the thickness of the support layer has an insignificant effect on the stress on the top surface of the soil foundation and the deflection of the top surface of the subgrade. The modulus of the track bed slab can affect the lateral force and deflection of the track bed slab, but it only slightly affects the longitudinal force and deflection of the track bed slab and the longitudinal and lateral force and deflection of the soil foundation. The modulus of the supporting layer only slightly affects the vertical and horizontal force and deflection of the track bed slab and soil foundation. The soil foundation modulus has the greatest influence on the vertical and horizontal forces and deflection of the track bed slab and soil foundation.

Experimental study and numerical modelling on the performance of circular footing resting on geogrid—reinforced granular soil bed

Experimental study and numerical modelling on the performance of circular footing resting on geogrid—reinforced granular soil bed

Experimental and intelligent modelling for predicting the amplitude of footing resting on geocell-reinforced soil bed under vibratory load

The reliable estimation of displacement amplitude is the prime factor for the design of geo-structures supporting the vibration loads. Currently, very subtle knowledge is available to compute the displacement amplitude of footing resting on the geocell-reinforced bed subjected to vibration loading. The advent of artificial intelligence modelling has antiquated many traditional approaches. Thus, in the present study, a novel hybrid paradigm has been developed by combining the artificial neural network (ANN) with dragonfly optimizer (DFO), abbreviated as ANN-DFO. To train and test the model, the reliable database was developed by conducting extensive field vibration tests. To establish the specific prediction target for the proposed model, displacement amplitude (da) was considered as an output index. A combination of parameters involving properties of foundation bed, geocell reinforcement, and dynamic excitation has been considered as input variables. Along with the standalone ANN model, the predictive veracity of the ANN-DFO was also compared with three other robust machine learning models, namely, Gaussian process regression (GPR), random forest (RF), and M−5 rules. Primarily, the forecasting ability of the developed models was assessed based on rigorous statistical criteria and a multi-criteria approach. Moreover, the model is also validated against the entirely new independent data which is not part of the original dataset. From the results, ANN-DFO model has shown a superior performance in predicting the displacement amplitude of footing resting on geocell-reinforced beds as compared to the other benchmark models. Finally, the strength of input variables on the estimation of displacement amplitude was highlighted using the sensitivity analysis.

Peer review of the pesticide risk assessment of the active substance oxamyl.

The conclusions of the EFSA following the peer review of the initial risk assessments carried out by the competent authorities of the rapporteur Member State, Italy, and co‐rapporteur Member State, France, for the pesticide active substance oxamyl and the assessment of applications for maximum residue levels (MRLs) are reported. The context of the peer review was that required by Commission Implementing Regulation (EU) No 844/2012, as amended by Commission Implementing Regulation (EU) No 2018/1659. The conclusions were reached on the basis of the evaluation of the representative uses of oxamyl as a nematicide on potato and tobacco (field use), on tomato (permanent greenhouse), on cucurbits (edible and inedible peel), pepper, aubergine and plants nurseries of the above‐mentioned crops on soil bed preparation (permanent greenhouse). The reliable end points, appropriate for use in regulatory risk assessment and the proposed MRLs, are presented. Missing information identified as being required by the regulatory framework is listed. Concerns are identified.

Surveys of community garden affiliates and soils in Houston, Texas.

Although urban community food gardens have the capacity to strengthen and support neighborhoods in need, the benefits of such operations must be considered in tandem with the potential risks associated with urban environmental contamination. Therefore, research is needed to characterize existing community gardens in urban areas. In the present study, a survey of Houston, TX, community gardeners (N = 20) was conducted to better understand their risk-based knowledge and perceptions, current gardening practices, and willingness to implement risk mitigation measures. Soil samples collected from the beds (N = 22) and surrounding grounds (N = 24) of existing community garden sites in Houston, TX, were screened for trace and heavy metals using X-ray fluorescence spectrometry. The survey indicated that community gardeners had few concerns with regard to potential soilborne hazards and were generally willing to use diverse strategies to reduce potential hazards related to garden soil contamination. Ground and garden bed soil collected from community gardens were found to have excess concentrations of arsenic compared to federal health screening limits. The information provided here provides insight into possible discordance between community gardening risk perception and contamination risk that could be addressed through outreach, engagement, and remediation approaches.

Efficacy Assessment of Silty–Sandy Soil as Bed Material in Constructed Wetland to Treat Naphthalene-Laden Wastewater: Physical and Numerical Modeling

Naphthalene is a common polycyclic aromatic hydrocarbon that is widely present in aquatic environments and has colossal negative health effects on living beings. Thus, the removal of naphthalene from wastewater using sustainable, low-cost geomaterials and novel technologies is of prime importance. In this study, the efficacy of a locally available silty–sandy soil in attenuating aqueous naphthalene was assessed using a laboratory-scale constructed wetland. The hydraulic conductivity of the soil was found to be 1.66 × 10−5 cm/s. Batch adsorption data showed that the Langmuir and pseudo-second-order models were the best fitting isotherm and kinetics models, with coefficient of determination values of 0.98 and 0.99, respectively. A one-dimensional vertical-column study using the tested soil on naphthalene showed that the exhaustion time of a 40-mm-deep soil bed was about 1.6 days. A laboratory-scale rectangular-tank test conducted using that soil, with the same test numerically modeled using HYDRUS solute-transport software, revealed that 90% of the initial concentration of naphthalene would reach the outlet in 102 days. The wetland constructed using the selected soil indicated a reduction in the naphthalene concentration of up to 92.8%, which corroborated the results from the CW2D HYDRUS module.