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2 pages, 154 KiB

Open AccessEditorial

Special Issue on Advances in Soil Pollution and the Geotechnical Environment

by Bing Bai

Appl. Sci. 2022, 12(23), 12000; https://0-doi-org.brum.beds.ac.uk/10.3390/app122312000 - 24 Nov 2022

Cited by 1 | Viewed by 847

Abstract

Soil pollution and disposal technology is currently a hot topic in geo-environmental engineering that involves the interaction mechanisms, migration processes, and treatment measures of various types of pollutants (e [...] Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

Research

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17 pages, 4637 KiB

Open AccessArticle

Occurrence Characteristics of Inorganic Nitrogen in Groundwater in Silty-Clay Riparian Hyporheic Zones under Tidal Action: A Case Study of the Jingzi River in Shanghai, China

by Yi Cai, Jingwen Xing, Ruoyao Huang, Xike Ruan, Nianqing Zhou and Dongze Yi

Appl. Sci. 2022, 12(15), 7704; https://0-doi-org.brum.beds.ac.uk/10.3390/app12157704 - 30 Jul 2022

Cited by 2 | Viewed by 1317

Abstract

For comprehending the effect of tidal action on nitrogen cycle in silty-clay riparian hyporheic zones, the synchronous monitoring of water level and water quality was carried out along a test transect during a spring tidal period from 21 to 23 October 2021. Moreover, [...] Read more.

For comprehending the effect of tidal action on nitrogen cycle in silty-clay riparian hyporheic zones, the synchronous monitoring of water level and water quality was carried out along a test transect during a spring tidal period from 21 to 23 October 2021. Moreover, the permeability and chemical composition of soil samples from drilled holes were measured. Subsequently, the spatiotemporal variation of inorganic nitrogen concentrations in the groundwater in the riparian hyporheic zone was investigated during the study period, and the potential reason was discussed. It is shown that the delayed response time of groundwater level in the silty-clay riparian zone to the tide-driven fluctuation of the river stage increased with distance from the shore and reached 3.0 h at the position 3.83 m away from the shore. The continuous infiltration of the river water under tide action contributed to the aerobic and neutral riparian hyporheic zone conductive to nitrification. Within 4 m away from the bank, the dominant inorganic nitrogen form changed from

{NO}_{3}^{-}

-N to

{NH}_{4}^{+}

-N, upon increasing the distance from the bank. Additionally, the removal of nitrogen could occur in the riparian hyporheic zone with aerobic and neutral environment under the conjoint control of nitrification, microbial assimilation, and aerobic denitrification. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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17 pages, 5181 KiB

Open AccessArticle

Screening Additives for Amending Compacted Clay Covers to Enhance Diffusion Barrier Properties and Moisture Retention Performance

by Min Wang, Jiaming Wen, Heng Zhuang, Weiyi Xia, Ningjun Jiang and Yanjun Du

Appl. Sci. 2022, 12(14), 7341; https://0-doi-org.brum.beds.ac.uk/10.3390/app12147341 - 21 Jul 2022

Cited by 4 | Viewed by 1447

Abstract

The cover systems in contaminated sites have some problems, including desiccation cracks, which would lead to degradation of the barrier performance. This study presented a systemic laboratory experimental investigation on the liquid–plastic limit, moisture retention, hydraulic conductivity (k), and gas diffusion [...] Read more.

The cover systems in contaminated sites have some problems, including desiccation cracks, which would lead to degradation of the barrier performance. This study presented a systemic laboratory experimental investigation on the liquid–plastic limit, moisture retention, hydraulic conductivity (k), and gas diffusion barrier properties of amended compacted clay by attapulgite and diatomite for controlling desiccation cracks and migration of water and volatile organic compounds (VOCs). The results showed that the attapulgite could enhance the moisture retention and liquid limit of amended compacted clay. Diatomite could reduce the gas diffusion coefficient (D_θ) significantly. The compacted clay amended by the dual-additives component of attapulgite and diatomite could enhance the liquid limit, moisture retention percent, gas barrier property, and hydraulic performance compared with the unamended clay. Based on the experimental data obtained, the dosage of additives was targeted to be 5%. The moisture retention percent of dual-additives (attapulgite 4% and diatomite 1%) amended clay increased by 82%, the k decreased by 25%, and the D_θ decreased by 42% compared with unamended clay. Scanning electron microscopy (SEM), BET-specific surface area test method (BET), Mercury Intrusion Porosimetry (MIP), and thermogravimetric analysis (TGA) indicated the enhancement mechanism of additives-amended compacted clay. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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9 pages, 1937 KiB

Open AccessArticle

A Calculation Method of Thermal Pore Water Pressure Considering Overconsolidation Effect for Saturated Clay

by Gailei Tian and Zhihong Zhang

Appl. Sci. 2022, 12(13), 6325; https://0-doi-org.brum.beds.ac.uk/10.3390/app12136325 - 21 Jun 2022

Cited by 1 | Viewed by 1282

Abstract

With the increase of soil consolidation degree, the pore water pressure induced by thermal loading drops dramatically. To conveniently and quickly calculate the thermal pore water pressure inside the soil under different overconsolidation states and quantify overconsolidation effect on thermal pore water pressure, [...] Read more.

With the increase of soil consolidation degree, the pore water pressure induced by thermal loading drops dramatically. To conveniently and quickly calculate the thermal pore water pressure inside the soil under different overconsolidation states and quantify overconsolidation effect on thermal pore water pressure, a calculation method of thermal pore water pressure considering overconsolidation effect for saturated clay is proposed. The method is verified by the relevant experimental data, and good agreements were achieved. Through analyzing the influence mechanism of OCR on the thermal pore water pressure, three important findings were captured. (1) For overconsolidated clay, thermal pore water pressure decreases nonlinearly with the increase of OCR. (2) There is a critical threshold of OCR 4.3; when 1 < OCR ≤ 4.3 (slightly overconsolidated state), the ratio of compression line slope to recompression line slope (Λ) of overconsolidated clay is consistent with that of the normally consolidated clay, while when OCR > 4.3 (highly overconsolidated state), the value of Λ is smaller than that of normally consolidated clay. (3) For highly overconsolidated clay (OCR > 4.3), considering the reducing of Λ with OCR, the prediction accuracy of the thermal pore pressure calculation method has been greatly improved; especially when OCR equals 30, the prediction accuracy improves by 92.7% as temperature change achieves 35 °C. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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17 pages, 6130 KiB

Open AccessArticle

Experimental Study on the Shear Strength of Silt Treated by Xanthan Gum during the Wetting Process

by Junran Zhang, Zhihao Meng, Tong Jiang, Shaokai Wang, Jindi Zhao and Xinxin Zhao

Appl. Sci. 2022, 12(12), 6053; https://0-doi-org.brum.beds.ac.uk/10.3390/app12126053 - 14 Jun 2022

Cited by 13 | Viewed by 1991

Abstract

Traditional materials such as fly ash and lime are generally used to improve soils but can severely pollute the environment. Eco-friendly protocols, such as the application of xanthan gum, are therefore essential for soil treatment. In this study, a series of microscopic tests, [...] Read more.

Traditional materials such as fly ash and lime are generally used to improve soils but can severely pollute the environment. Eco-friendly protocols, such as the application of xanthan gum, are therefore essential for soil treatment. In this study, a series of microscopic tests, water retention characteristics tests, and shear tests were carried out on silt, which are known to have poor engineering properties, to explore the effect and mechanism of xanthan gum treatment on the water retention and shear strength characteristics of silt during the wetting process. The results show that the water retention capacity of the treated silt increases with increasing xanthan gum content, and a hysteresis effect is clearly observed. The cohesion and internal friction angle of the silt strongly decrease with increasing water content, and the strength significantly weakens. However, the strength of the silt treated with xanthan gum is consistently higher than that of the untreated silt. The microscopic tests show that soil pores are gradually filled by xanthan gum with good water-retaining properties, thus significantly enhancing the water retention capacity. Furthermore, the hydrogel that cements the soil particles forms by the bonding effects between xanthan gum and soil particles, which greatly improves the silt strength. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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14 pages, 3103 KiB

Open AccessArticle

Long-Term Performance of the Water Infiltration and Stability of Fill Side Slope against Wetting in Expressways

by Yuedong Wu, Xiangyu Zhou and Jian Liu

Appl. Sci. 2022, 12(12), 5809; https://0-doi-org.brum.beds.ac.uk/10.3390/app12125809 - 7 Jun 2022

Cited by 2 | Viewed by 1391

Abstract

Different settlements and instabilities of unsaturated subgrade subjected to wetting have been paid increasing attention in the southeast coastal areas of China. However, the treatments are costly when they are used in engineering. In addition, the long-term performances of the treatments are unclear. [...] Read more.

Different settlements and instabilities of unsaturated subgrade subjected to wetting have been paid increasing attention in the southeast coastal areas of China. However, the treatments are costly when they are used in engineering. In addition, the long-term performances of the treatments are unclear. Based on seepage theory for unsaturated soils, a novel subgrade using a capillary barrier was proposed in this study to reduce the different settlements and stabilities. Compared with previous studies, a capillary barrier was merely applied in the landfill. The long-term performance and feasibility of a capillary barrier applied in a tilted subgrade slope is worthy of study, particularly in humid climates. Using Geo-Studio, the feasibility was verified by comparing a conventional subgrade with a subgrade using a capillary barrier in southeast coastal areas in terms of pore-water pressure, water content, settlement, and the safety factor. The numerical results showed that the subgrade using a capillary barrier could provide significant improvements in the performance of reducing the impact of pore-water pressure distribution it suffered from, so as to lead to smaller different settlements. The vertical settlement of the pavement using a capillary barrier over a 1 year period was 1 cm. Compared with a conventional subgrade, the settlement fell by 94%, and the safely factor increased by 15% for the subgrade using the capillary barrier. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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13 pages, 5029 KiB

Open AccessArticle

An Experimental Study on the Migration of Pb in the Groundwater Table Fluctuation Zone

by Jihong Qu, Tiangang Yan, Yifeng Zhang, Yuepeng Li, Ran Tian, Wei Guo and Jueyan Jiang

Appl. Sci. 2022, 12(8), 3870; https://0-doi-org.brum.beds.ac.uk/10.3390/app12083870 - 12 Apr 2022

Cited by 2 | Viewed by 1301

Abstract

As a result of fluctuations in the shallow groundwater table, hydrodynamic conditions change alongside environmental conditions and hydrogeochemical processes to affect pollutant migration. The study aimed to investigate the migration, adsorption, and desorption characteristics of Pb on fine, medium, and coarse sand in [...] Read more.

As a result of fluctuations in the shallow groundwater table, hydrodynamic conditions change alongside environmental conditions and hydrogeochemical processes to affect pollutant migration. The study aimed to investigate the migration, adsorption, and desorption characteristics of Pb on fine, medium, and coarse sand in the water table fluctuation zone by using several laboratory methods, including the kinetic aspects of Pb²⁺ adsorption/desorption and water table fluctuation experiments. The results showed that the adsorption and desorption curves fit the Elovich equation well at a correlation coefficient above 0.9. In the adsorption and desorption kinetic experiments for fine, medium, and coarse sand collected and from the floodplain, the maximum adsorption capacity of Pb²⁺ was 2367 mg·kg⁻¹, 1848 mg·kg⁻¹, and 1544 mg·kg⁻¹, respectively. The maximum desorption capacity of Pb²⁺ was 29.18 mg·kg⁻¹, 62.38 mg·kg⁻¹, and 81.60 mg·kg⁻¹, respectively. In environments with pH greater than 4, the adsorption capacity was proportional to the pH, but the desorption capacity decreased as the pH increased in water. As the water table varied, the lowest pH occurred in the polluted medium we set initially. When the distance between the pollutants and sample solution grew further, pH increased, and the Pb²⁺ concentration decreased in the sample solution. In the column experiment of water table fluctuations on coarse sand, Pb²⁺ migrated nearly 5 cm upward from the original pollutant and migrated less than 10 cm downward from that. In our experiments on medium and fine sand, the upward and downward migration distances were <5 cm. The groundwater table fluctuations, pH variation, and Pb concentration currently influence the migration of Pb. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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21 pages, 9191 KiB

Open AccessArticle

Experimental and Simulation Research on the Process of Nitrogen Migration and Transformation in the Fluctuation Zone of Groundwater Level

by Yuepeng Li, Liuyue Wang, Xun Zou, Jihong Qu and Gang Bai

Appl. Sci. 2022, 12(8), 3742; https://0-doi-org.brum.beds.ac.uk/10.3390/app12083742 - 8 Apr 2022

Cited by 2 | Viewed by 1865

Abstract

The fluctuation of groundwater causes a change in the groundwater environment and then affects the migration and transformation of pollutants. To study the influence of water level fluctuations on nitrogen migration and transformation, physical experiments on the nitrogen migration and transformation process in [...] Read more.

The fluctuation of groundwater causes a change in the groundwater environment and then affects the migration and transformation of pollutants. To study the influence of water level fluctuations on nitrogen migration and transformation, physical experiments on the nitrogen migration and transformation process in the groundwater level fluctuation zone were carried out. A numerical model of nitrogen migration in the Vadose zone and the saturated zone was constructed by using the software HydrUS-1D. The correlation coefficient and the root mean square error of the model show that the model fits well. The numerical model is used to predict nitrogen migration and transformation in different water level fluctuation scenarios. The results show that, compared with the fluctuating physical experiment scenario, when the fluctuation range of the water level increases by 5 cm, the fluctuation range of the nitrogen concentration in the coarse sand, medium sand and fine sand media increases by 37.52%, 31.40% and 21.14%, respectively. Additionally, when the fluctuation range of the water level decreases by 5 cm, the fluctuation range of the nitrogen concentration in the coarse sand, medium sand and fine sand media decreases by 36.74%, 14.70% and 9.39%, respectively. The fluctuation of nitrogen concentration varies most significantly with the amplitude of water level fluctuations in coarse sand; the change in water level has the most significant impact on the flux of nitrate nitrogen and has little effect on the change in nitrite nitrogen and ammonium nitrogen, and the difference in fine sand is the most obvious, followed by medium sand, and the difference in coarse sand is not great. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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16 pages, 7552 KiB

Open AccessArticle

The Effects of the Long-Term Freeze–Thaw Cycles on the Forms of Heavy Metals in Solidified/Stabilized Lead–Zinc–Cadmium Composite Heavy Metals Contaminated Soil

by Zhongping Yang, Jiazhuo Chang, Xuyong Li, Keshan Zhang and Yao Wang

Appl. Sci. 2022, 12(6), 2934; https://0-doi-org.brum.beds.ac.uk/10.3390/app12062934 - 13 Mar 2022

Cited by 10 | Viewed by 2154

Abstract

Heavy metals (HMs) exist in nature in different forms, and the more unstable the form of an HM, the higher its toxicity and bioavailability. The content of HMs in stable fractions can increase significantly through the stabilization/solidification (S/S) technology. Still, external environments such [...] Read more.

Heavy metals (HMs) exist in nature in different forms, and the more unstable the form of an HM, the higher its toxicity and bioavailability. The content of HMs in stable fractions can increase significantly through the stabilization/solidification (S/S) technology. Still, external environments such as freeze–thaw (F–T) cycles will affect the stability of HMs directly. Therefore, a long-term F–T study of S/S Pb–Zn–Cd composite HM-contaminated soil was conducted under six conditions (0, 3, 7, 14, 30, and 90 cycles) with each F–T cycle process up to 24 h. The improved Tessier method was employed, and the results show that the S/S technology makes HMs transform to a more stable fraction. Still, the transformation efficiency is different for each HM. More than 98% of lead and zinc were converted to stable forms, while for cadmium, there are only 75.1%. Meanwhile, the S/S HMs were rapidly transformed into unstable forms at 0–14 cycles, but after 14 cycles, the transformation speed was significantly reduced. Among stable forms, it is mainly that the carbonate-bound fraction of HMs changes to unstable forms, and the characteristic peaks of carbonate stretching vibration were found at 874 cm⁻¹, and 1420 cm⁻¹ by Fourier infrared spectroscopy proves the presence of carbonate-bound substances. As a result of this study, the change trend of contaminated soil with S/S HMs under the effect of long-term F–T cycle was revealed, and the crisis point of pollution prevention and control was found, which provides some theoretical basis for the safety of soil remediation project. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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15 pages, 4530 KiB

Open AccessArticle

Molecular Dynamics Simulation of Nanoscale Elastic Properties of Hydrated Na-, Cs-, and Ca-Montmorillonite

by Lianfei Kuang, Qiyin Zhu, Xiangyu Shang and Xiaodong Zhao

Appl. Sci. 2022, 12(2), 678; https://0-doi-org.brum.beds.ac.uk/10.3390/app12020678 - 11 Jan 2022

Cited by 7 | Viewed by 3196

Abstract

The knowledge of nanoscale mechanical properties of montmorillonite (MMT) with various compensation cations upon hydration is essential for many environmental engineering-related applications. This paper uses a Molecular Dynamics (MD) method to simulate nanoscale elastic properties of hydrated Na-, Cs-, and Ca-MMT with unconstrained [...] Read more.

The knowledge of nanoscale mechanical properties of montmorillonite (MMT) with various compensation cations upon hydration is essential for many environmental engineering-related applications. This paper uses a Molecular Dynamics (MD) method to simulate nanoscale elastic properties of hydrated Na-, Cs-, and Ca-MMT with unconstrained system atoms. The variation of basal spacing of MMT shows step characteristics in the initial crystalline swelling stage followed by an approximately linear change in the subsequent osmotic swelling stage as the increasing of interlayer water content. The water content of MMT in the thermodynamic stable-state conditions during hydration is determined by comparing the immersion energy and hydration energy. Under this stable hydration state, the nanoscale elastic properties are further simulated by the constant strain method. Since the non-bonding strength between MMT lamellae is much lower than the boning strength within the mineral structure, the in-plane and out-of-plane strength of MMT has strong anisotropy. Simulated results including the stiffness tensor and linear elastic constants based on the assumption of orthotropic symmetry are all in good agreement with results from the literature. Furthermore, the out-of-plane stiffness tensor components of C₃₃, C₄₄, and C₅₅ all fluctuate with the increase of interlayer water content, which is related to the formation of interlayer H-bonds and atom-free volume ratio. The in-plane stiffness tensor components C₁₁, C₂₂, and C₁₂ decrease nonlinearly with the increase of water content, and these components are mainly controlled by the bonding strength of mineral atoms and the geometry of the hydrated MMT system. Young’s modulus in all three directions exhibits a nonlinear decrease with increasing water content. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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13 pages, 2272 KiB

Open AccessArticle

Experimental Study on Microstructure of Unsaturated Expansive Soil Improved by MICP Method

by Xinpei Yu, Hongbin Xiao, Zhenyu Li, Junfeng Qian, Shenping Luo and Huanyu Su

Appl. Sci. 2022, 12(1), 342; https://0-doi-org.brum.beds.ac.uk/10.3390/app12010342 - 30 Dec 2021

Cited by 10 | Viewed by 2521

Abstract

The soil water characteristic curve and microstructure evolution of unsaturated expansive soil improved by microorganisms in Nanning, Guangxi were studied by means of filter paper method and scanning electron microscope imaging (SEM). Based on Fredlung & Xing model, the influence law of different [...] Read more.

The soil water characteristic curve and microstructure evolution of unsaturated expansive soil improved by microorganisms in Nanning, Guangxi were studied by means of filter paper method and scanning electron microscope imaging (SEM). Based on Fredlung & Xing model, the influence law of different cement content on the soil water characteristic curve of improved expansive soil is proved. According to the analysis of SEM test results, the influence mechanism of MICP method on the engineering characteristics of improved expansive soil is revealed. The results show that with the increase of cement content, the saturated water content and residual water content of the improved expansive soil gradually increased. At the same time, the water stability gradually increased while the air inlet value gradually decreased. The improved expansive soil changes from the superposition of flat particles and flake particles to the contact between spherical particles and flake particles, which indicates that the aggregate increases significantly. With the increase of the content of cement solution, the contact between particles tends to be smooth and the soil pores gradually tend to be evenly distributed. The particle size and microstructure of soil particles was changed and the connection between particles was enhanced in the improved expansive soil. Eventually the strength and water stability of expansive soil were improved. The conclusions above not only provide a theoretical basis for the in-depth study of engineering characteristics of unsaturated expansive soil improved by MICP method, but also offer theoretical evidence for perfecting engineering technology of expansive soil improved by MICP method. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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15 pages, 4951 KiB

Open AccessArticle

Experimental Investigation on the Effects of Ethanol-Enhanced Steam Injection Remediation in Nitrobenzene-Contaminated Heterogeneous Aquifers

by Ruxue Liu, Xinru Yang, Jiayin Xie, Xiaoyu Li and Yongsheng Zhao

Appl. Sci. 2021, 11(24), 12029; https://0-doi-org.brum.beds.ac.uk/10.3390/app112412029 - 17 Dec 2021

Cited by 3 | Viewed by 2067

Abstract

Steam injection is an effective technique for the remediation of aquifers polluted with volatile organic compounds. However, the application of steam injection technology requires a judicious selection of stratum media because the remediation effect of hot steam in heterogeneous layers with low permeability [...] Read more.

Steam injection is an effective technique for the remediation of aquifers polluted with volatile organic compounds. However, the application of steam injection technology requires a judicious selection of stratum media because the remediation effect of hot steam in heterogeneous layers with low permeability is not suitable. In this study, the removal effect of nitrobenzene in an aquifer was investigated through a series of two-dimensional sandbox experiments with different stratigraphic structures. Four types of alcohols were used during steam injection remediation to enhance the removal effect of nitrobenzene (NB)-contaminated heterogeneous aquifers. The principle of the removal mechanism of alcohol-enhanced organic compounds is that alcohols can reduce the surface tension of the contaminated water, resulting in Marangoni convection, thereby enhancing mass and heat transfer. The addition of alcohol may also reduce the azeotropic temperature of the system and enhance the volatility of organic compounds. The study revealed that all four alcohol types could reduce the surface tension from 72 mN/m to <30 mN/m. However, among these, only ethanol reduced the azeotropic temperature of NB by 15 °C, thereby reducing energy consumption and remediation costs. Therefore, ethanol was selected as an enhancing agent to reduce both surface tension and azeotropic temperature during steam injection. In the 2-D simulation tank, the interface between the low-and high-permeability strata in the layered heterogeneous aquifer had a blocking effect on steam transportation, which in turn caused a poor remediation effect in the upper low-permeability stratum. In the lens heterogeneous aquifer, steam flows around the lens, thereby weakening the remediation effect. After adding ethanol to the low-permeability zone, Marangoni convection was enhanced, which further enhanced the mass and heat transfer. In the layered and lens heterogeneous aquifers, the area affected by steam increased by 13% and 14%, respectively. Moreover, the average concentration of NB was reduced by 51% in layered heterogeneous aquifers and by 58% in low-permeability lenses by ethanol addition. These findings enhance the remediation effect of steam injection in heterogeneous porous media and contribute to improve the remediation efficiency of heterogeneous aquifers by steam injection. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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9 pages, 1850 KiB

Open AccessArticle

Use of Foamed Cement Banking for Reducing Expressways Embankment Settlement

by Yuedong Wu, Hui Liu and Jian Liu

Appl. Sci. 2021, 11(24), 11959; https://0-doi-org.brum.beds.ac.uk/10.3390/app112411959 - 15 Dec 2021

Cited by 2 | Viewed by 2078

Abstract

Expressways are often built on soft ground, the foundation of which is not processed adequately during the construction period. Consequently, the traffic safety and embankment stability will be seriously affected due to uneven settlement. The technology of holing the embankment and replacing foamed [...] Read more.

Expressways are often built on soft ground, the foundation of which is not processed adequately during the construction period. Consequently, the traffic safety and embankment stability will be seriously affected due to uneven settlement. The technology of holing the embankment and replacing foamed cement banking (FCB) could control the settlement of an embankment without road closure, thus reduce the impact of construction on normal operation of highways. In this paper, the principle of FCB is described. Additionally, a sedimentation ratio calculation method, through the analysis of the settlement load ratio, is proposed for calculating the roadbed replacement thickness. This paper takes the example of the test section EK0 + 323 on Shen-Jia-Hu expressway in Zhejiang Province and combines with site settlement monitoring data to confirm the effectiveness of the calculation method proposed. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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15 pages, 6837 KiB

Open AccessArticle

Analysis of Hydrogeochemical Characteristics and Origins of Chromium Contamination in Groundwater at a Site in Xinxiang City, Henan Province

by Wenfang Chen, Yaobin Zhang, Weiwei Shi, Yali Cui, Qiulan Zhang, Yakun Shi and Zexin Liang

Appl. Sci. 2021, 11(24), 11683; https://0-doi-org.brum.beds.ac.uk/10.3390/app112411683 - 9 Dec 2021

Cited by 10 | Viewed by 1835

Abstract

Hexavalent chromium contamination in groundwater has become a very serious and challenging problem. Identification of the groundwater chemical characteristics of the sites and their control mechanisms for remediation of pollutants is a significant challenge. In this study, a contaminated site in Xinxiang City, [...] Read more.

Hexavalent chromium contamination in groundwater has become a very serious and challenging problem. Identification of the groundwater chemical characteristics of the sites and their control mechanisms for remediation of pollutants is a significant challenge. In this study, a contaminated site in Xinxiang City, Henan Province, was investigated and 92 groundwater samples were collected from the site. Furthermore, the hydrogeochemical characteristics and the distribution patterns of components in the groundwater were analyzed by a combination of multivariate statistical analysis, Piper diagram, Gibbs diagram, ions ratio and hydrogeochemical simulation. The results showed that the HCO₃-Cl-Mg-Ca type, SO₄-HCO₃-Na type, and HCO₃-Mg-Ca-Na type characterize the hydrogeochemical composition of shallow groundwater and HCO₃-Cl-Mg-Ca type, HCO₃-Na-Mg type, and HCO₃-SO₄-Mg-Na-Ca type characterize the hydrogeochemical composition of deep groundwater. Ion ratios and saturation index indicated that the groundwater hydrogeochemical characteristics of the study area are mainly controlled by water–rock action and evaporative crystallization. The dissolution of halite, gypsum and anhydrite, the precipitation of aragonite, calcite and dolomite, and the precipitation of trivalent chromium minerals other than CrCl₃ and the dissolution of hexavalent chromium minerals occurred in groundwater at the site. The minimum value of pH in groundwater at the site is 7.55 and the maximum value is 9.26. The influence of pH on the fugacity state of minerals was further investigated. It was concluded that the saturation index of dolomite, calcite, aragonite and MgCr₂O₄ increases with the increase of pH, indicating that these minerals are more prone to precipitation, and the saturation index of Na₂Cr₂O₇, K₂Cr₂O₇ and CrCl₃ decreases with the increase of pH, implying that Na₂Cr₂O₇, K₂Cr₂O₇ and CrCl₃ are more prone to dissolution. The saturation index of the remaining minerals is less affected by pH changes. The study can provide a scientific basis for groundwater remediation. Full article

(This article belongs to the Special Issue Advances in Soil Pollution and Geotechnical Environment)

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