Soil In Coastal Area Research Articles

Electrodeposition of calcareous cement from seawater in marine silica sands

The erosion of marine sediments is a pressing issue for coastal areas worldwide. Established methods to mitigate coastal erosion fail to provide lasting and sustainable solutions to protect marine ecosystems. Here we demonstrate the application of mild electrical stimulations to precipitate calcareous mineral binders from seawater in the pores of marine soils via electrodeposition, an alternative approach to mitigating coastal erosion. Results of electrochemical laboratory experiments unveil that the polymorphs, precipitation sites, intrusion mechanisms, and effects of electrodeposited minerals in marine sands vary as a function of the magnitude and duration of applied voltage, soil relative density, and electrolyte ionic concentration. Surprisingly, in addition to the precipitation of calcium carbonate and magnesium hydroxide, the formation of hydromagnesite is also observed due to electrically driven fluctuations in the local pH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${pH}$$\\end{document}. These electrodeposits lead to enhanced mechanical and hydraulic properties of the marine sands, indicating that electrodeposition routes could be developed to reinforce marine soils in coastal areas that more closely mimic natural systems.

BIOCHAR AS A POTENTIAL SOIL CONDITIONER IN SALINE PRONE COASTAL AREA OF BANGLADESH

In the coastal areas of Bangladesh, salinity restricts normal crop production and increases with the desiccation of the soil. Recently, biochar has received great attention as a soil amendment to mitigate the detrimental effects of salinity stress. In this respect, a field experiment was conducted to examine the effects of biochars on soil properties and growth of okra (Abelmoschus esculentus L.) and to identify a suitable biochar amendment for salt-affected soils in coastal areas of Bangladesh. The experiment was conducted in a randomized complete block design (RCBD) with five replications. Three types of biochar (rice straw biochar, sawdust biochar and water hyacinth biochar) were applied @ 10 t ha-1 in a silt loam soil along with the control. Results showed that biochar application to the soil enhanced plant height, leaf number, leaf area, shoot fresh weight, shoot dry weight and yield of okra as well as improving the soil quality e.g. field capacity (FC), CEC, OC, total N, available P, S, K, and Ca. The application of water hyacinth biochar improved almost all of the growth and yield attributes of okra along with most of the soil properties than that of others. The results suggest that water hyacinth biochar might be recommended as a suitable soil amendment for better crop growth and soil quality. Moreover, water hyacinth biochar had significantly (P<0.001) higher surface area (205.40 m2g-1); consequently, higher capacity in salt and water adsorption which might prevent soil desiccation. Side by side, it significantly (P<0.001) increased the soil Ca content which might replace Na+ in the root rhizosphere minimizing the Na+ uptake by plants. Taken together, water hyacinth biochar could also be the best choice of organic amendments to reduce the suppressing effect of salinity stress in coastal areas of Bangladesh.

Spatial Variations in Salinity and Sodicity of Reclaimed Tideland Paddy Soils in Coastal Areas of Southwestern Korea

Spatial Variations in Salinity and Sodicity of Reclaimed Tideland Paddy Soils in Coastal Areas of Southwestern Korea

Behavior of cement-stabilized marine clay and pure clay minerals exposed to high salinity grout

Soil-cement columns created by the injection of grout into the soil are common in practice for stabilizing soft soil in coastal areas. The behavior of clay-cement under marine conditions, especially considering the effect of both the clay mineral type and water salinity, has been less considered. The current study investigated the effects of high salinity grout on the mechanical and the physical behavior of cement-stabilized marine clay at a range of cement contents and water-to-cement ratios. The performance of the cement-stabilized marine clay was compared with those of kaolinite as an inactive clay and bentonite as an active clay. The results showed that, when saline water was used in the soil–cement mixtures containing kaolinite or marine clay, there was no decrease in strength and the cement content had no effect on the results. For active bentonite at 5% and 10% cement contents, the curing time had a negative effect on the strength; over time, the strength of the mixtures decreased. In practice, there should be no concern about the use of saline water to create grout at cement contents greater that 15%. However, if the clayey soil contains active minerals, a cement content of less than 15% is not recommended.

Numerical study on coupled modelling of artificial freezing marine soil

A theoretical model is proposed to investigate the coupling of the hydro-ice-salt-crystalline-thermal-mechanical of the artificial frozen marine soil in coastal areas. The influence of non-convective and thermal permeability in the fields of salt, pressure, thermal, and water, the compressibility of solid particles, as well as solute potential and ice resistance coefficients in convective flux are comprehensively considered based on the mass, energy, and momentum conservation equations. The proposed coupling model is solved using the COMSOL Multiphysics software. The accuracy of the proposed theoretical model is verified by the model test results in the literature. The parametric studies are conducted to investigate the effects of the key parameters on the freezing process. It is found that the salt desorption of the frozen marine soil cannot be ignored. The effect of salt desorption in the frozen area is strong which makes the adsorbed salt content in the unfrozen area greater than that in the frozen area. The change in salt mass fraction has a great influence on the overall frost heave, salt heave and water freezing. With the increase of overburden, the soil is compressed and the desorption effect is enhanced in the frozen area.

Combination of organic soil amendments and weed control to optimize the growth and yield of peanuts in sandy soils in coastal areas

Sandy soils in coastal areas can be managed for peanut cultivation by minimizing the limiting factors. The study aimed to use organic soil amendments combined with weed control methods to optimize peanuts' growth and yield in sandy land. The research was conducted in the coastal area of Bengkulu, Indonesia, from September 2019 to January 2020. Two experimental factors were arranged in a completely randomized block design with three replications. The first was soil amendment consisted of cow manure (CM), the compost of empty fruit bunches of oil palm (EFB), and without soil amendment as a control, and the second was weed control methods consisted of preemergence application of oxyfluorfen, postemergence application of propaquizafop, and hand-weeding. The results found the most effective weed control in the EFB compost was hand-weeding, but in CM application was propaquizafop. The efficacy of propaquizafop was not significantly different from hand-weeding to control the sedges and grassy weeds. Plant growth improved, and the yield of peanuts increased by the CM and compost of EFB. Optimal growth and yield of peanuts were observed in the CM treatment, namely as the stover weight and pods yield of 28.74 g/plant and 5.82 tons/ha, respectively. With hand-weeding control, the peanut stover and pods yield was 28.79 g/plant and 5.78 tons/ha, respectively. The research provided novel information regarding the potential of the coastal land for peanut cultivation using local organic materials as soil amendments.

Cyclic and Post-Cyclic Behaviors of Stabilized Sand-Containing Soft Soil in Coastal Areas

Land resources are being depleted due to global climate change, and as a result, infrastructures such as expressways and high-speed railways have no option but to be built in soft soil regions. Hence, the cyclic and post-cyclic behaviors of soft soil are vitally important. However, little attention has been devoted to this issue. In the current study, a series of cyclic triaxial tests and standard monotonic loading tests were carried out in order to investigate the cyclic and post-cyclic behavior of stabilized sand-containing soft soil. In addition, the stiffness evolution index model was proposed to describe the characteristics of stiffness evolution. The results show that for a given number of loading cycles, stiffness almost linearly decreases with the increase in sand content. The higher the confining pressure is, the greater the stiffness is. The cement content has the greatest impact on the stiffness evolution index. The stiffness evolution index model can provide a good description of experimental data. The initial value of post-cyclic axial strain is non-zero due to the accumulative strain caused by previous cyclic loading. Post-cyclic stress increases rapidly within a small range of strain and can reach peak stress with great speed. The post-cyclic initial tangent modulus increases from 1602 kPa to 4803 kPa as the cement content increases from 6% to 12%.

Research on Influencing Factors of Consumption and Purchase Intention of Camellia Oil in Coastal Areas Based on Logistics Model

Camellia oil contains a variety of active substances, which have the functions of strengthening the heart and lowering cholesterol, and can prevent a variety of cardiovascular and cerebrovascular diseases caused by vascular sclerosis edible oil. Based on the logistics model, this paper builds a research model on the influencing factors of consumption and purchase intention and analyzes the coastal areas of camellia oil. Using this model, it makes an empirical analysis and research on the differences in the purchase intention and influencing factors of different consumers of camellia oil. Based on the results of empirical analysis, the main research conclusions of this paper are extracted, including the influencing factors of consumers’ camellia oil purchase willingness and the differences in the influencing factors of consumers’ camellia oil purchase willingness under different income levels, and put forward some corresponding measures and policy suggestions in a targeted manner. Based on the research model of the influencing factors of purchase intention established by logistic algorithm, this paper analyzes the coastal areas of Chashan oil and finds that the factors affecting consumers’ purchase intention are positively related to education and personal monthly income and negatively related to gender. “Educational education” is significant at 1% and has a positive correlation with a coefficient of 0.864; personal income is significant at 5% with a coefficient of 0.762; for gender, it is negatively correlated with a coefficient of -0.259, indicating that other variables remain unchanged. Education can promote consumers’ willingness to buy camellia oil, and consumers with higher education are more likely to buy camellia oil. In the same regression prediction model, the regression prediction efficiency of this model is better. In general, this shows that the model in this paper has certain superior performance.

Performance of salt-tolerant forage genotypes of millet Pennisetum glaucum (L.) R. Br.] in Eastern Mediterranean conditions

In this study the aim was to evaluate alternative crops able to tolerate thefuture rise in salinity, likely to occur in the East Mediterranean coastal areas. For this, two genotypes of pearl millet (Tall and IP13) were submitted to saline conditions (4, 8, 12 dS.m-1 and 2 dS.m-1 as control) in a field trial. Water consumption using neutron probe technique, physiological response and the production were studied. The neutron probe technique showed that 96% of consumed water originated in the upper 0.45 m. As salinity increased, water consumption became shallower, suggesting a different root distribution. Physiological aspects related to plant height, foliar potassium and uptake of nitrogen were investigated. Tallest plants were found in 4 dS.m-1 in Tall, and in 2 dS.m-1 in IP13. Foliar potassium was similar in Tall variety, while IP13 excluded the potassium, in order to reduce cellular ions. In Tall the 15N technique showed that 40-50% of plant N originated from the fertilizers, irrespective of saline conditions. Fresh weight was not different between 4 and 8 dS.m-1, in three cuts out of five in 2016 and 2017. Tall produced higher dry matter, especially under saline conditions. Best water use efficiency was in 4 dS.m-1 (10.4 kg.m-3 in Tall; 8.8 kg.m-3 in IP13). The plotting of dry matter production against salinity gave quadratic equations, with a peak at 5.6 dS.m-1 for IP13 and 7.1 dS.m-1 for Tall. Tall can be used for phytoremediation of soils in coastal areas, and as a forage crop.

An improved cellular automata model for soil erosion in coastal areas based on discrete physical variables

AbstractSoil erosion is a major and costly environmental hazard worldwide. Obtaining a thorough understanding of the soil erosion process is essential for erosion control. The high erodibility of the saline‐sodic soil in coastal areas causes rills to develop rapidly and erosion patterns change substantially during the rainfall process. Understanding the temporal and spatial dynamics of the soil surface morphology is crucial for revealing the mechanism behind the severe soil erosion process, but simulating these dynamics with many existing empirical or physical models is difficult. Cellular automata (CA) provides a simple alternative approach with high computational efficiency for modelling the complex patterns of soil erosion evolution using local interactions rules. However, previously established CA models poorly simulated the lateral erosion. By dividing the runoff amount into a discrete variable of every constituent cell and considering the runoff flow velocity when calculating the flow direction, the CA model developed here, based on discrete physical variables (CADV), could simulate soil erosion rate dynamics and rill morphological development with low relative errors. The variations in the simulated sediment yield rates during rainfall events were consistent with the experimental measurements, and the relative errors of cumulative sediment yields between the simulated and measured values were lower than 5% from the 38th to 60th min (the end of rainfall event) during the rainfall. The morphological characteristics of slope erosion with relative errors in rill length, rill width, and rill depth were lower than 5% at specific times during rainfall events. Specifically, regarding the rill width parameter, the relative errors of the maximum and average rill widths were both lower than 5% when the rainfall event ended at the 60th min. The results show that the CADV is an appropriate tool for describing the soil erosion process and improving our understanding of the erosion process characteristics of saline‐sodic soil slopes in a coastal region of China.Highlights Cellular automata based on discrete variables (CADV) improves soil erosion simulation. CADV simulates soil loss and rill morphological development with low relative errors. CADV improves insight into the mechanism of soil erosion in coastal area. CADV provides a new approach to improve soil erosion modelling with cellular automata.

Variations in peat soil properties at the west coast of Sumatra Island

Peat in coastal areas has different characteristics compared to peat in inland areas because coastal peat usually has high DHL, pyrite, marine sandy substratum, and maturity which is generally classified as hemic to sapric. These variants in soil characteristics drive peculiarity in its management. For this reason, a more detailed information about the characteristics is needed to allow sustainable management and utilization. A total of 78 peat soil samples from 20 peat soil profiles taken over west coast of Sumatra was studied and analyzed for their physical and chemical properties. Field observations were made using a peat auger to determine thickness and maturity, substratum, presence of pyrite, and others. Results showed that peat thickness varied from shallow (50-100 cm), medium (100-200 cm), to very deep (>700 cm); peat situated closer to the coast generally has shallow peat depth. Peat soil in coastal areas contained a mineral soil substrate with a sand content of >70%. It was found that soil had a hemic maturity level and a very acidic to acidic pH value (pH 2.5-5.4). The P2O5 content extracted by 25% HCl varied from low to moderate, while K2O content of 25% HCl extraction was very low. Cations K, Na, and Ca were very low to very high, while Mg spanned from very low to high. Based on its thickness, 25% of peatland were not suitable (Nrc) for general agriculture uses because of >300 cm thickness. Therefore, it is necessary to improve soil fertility and water management in several places.

Analysis of ground deformation development and settlement prediction by air-boosted vacuum preloading

Vacuum preloading has been widely used to improve soft soils in coastal areas of China. An increasing amount of evidence from field operations has shown that conventional vacuum preloading is prone to clogging in prefabricated vertical drains (PVDs) and demands a large volume of sand fills. In recent years, air-boosted vacuum preloading has been developed to overcome these limitations; however, this method still requires more data to verify its performance. In this study, a field test for air-boosted vacuum preloading was conducted, and a large-strain two-dimensional (2D) finite element (FE) model was developed and validated against the field test data. Then, a series of FE parametric analyses was performed to assess key factors, i.e. the air injection pressure, the injection spacing, and the characteristics of cyclic injection, which affect the performance of the air-boosted vacuum preloading. The results showed that the ground settlement and lateral displacement of the soils increased due to an increase in the injection pressure, a decrease in the injection spacing, or increases in the number and duration of the injection cycles. Based on the parametric analyses, an empirical formula for ground settlement prediction was proposed and compared with a case history reported in the literature, showing good agreement.

Spatial Variability of the Mechanical Parameters of High-Water-Content Soil Based on a Dual-Bridge CPT Test

Soft soil generally has a high water content, and the accurate quantification of its mechanical parameters is an important aspect of foundation design and disaster prevention. The mechanical parameters of soft soil have significant spatial variability or heterogeneity due to the complex deposition process of soil, leading to the high uncertainty of the quantifications of its parameters. Therefore, understanding the spatial variability of the parameters is an important approach to reduce uncertainty. In this study, the high-resolution (0.1 m) tip resistance (qc) and side friction (fs) of 18 soft soils in coastal areas were measured using the Dual-bridge CPT in-situ test. The vertical and horizontal variabilities of qc and fs were investigated using the random field theory. The results showed that both qc and fs are stationary and ergodic. The coefficient of variation of vertical fs is much higher than that of qc. On the one hand, fs may be vulnerable to noise, and its test accuracy is lower than qc; on the other hand, it may be that the spatial variability of the residual strength of soft soil may be greater than that of its failure strength. The horizontal correlation distance and coefficient of variation of qc and fs have no obvious change trend along the depth direction, but compared with the coefficient of variation curve, it was found that the change trends of qc and fs are basically the same, which is considered to be related to the properties of the soil layer. The research results can provide support for the spatial variability evaluation and reliability analysis of soft-soil engineering in this area. At the same time, it can also provide a theoretical basis for the layout of exploration engineering and sampling spacing.

EFFECT OF BIODIVE FERTILIZER ON N, P, AND K NUTRITION STATUS AND GROWTH AND RESULT OF TWO GOGO RICE VARIETIES IN COASTAL AREA

This study aims to determine the effectiveness of the application of biological fertilizers on the availability of nutrients N, P, and K in the soil in coastal areas and the yield of upland rice varieties Inpago 10 and Sunggau. This research was conducted from September to December 2019 in Beringin Raya Village, Muara Bangkahulu District, Bengkulu City. The experimental design used was a two-factor Completely Randomized Block Design. The first factor is land rice varieties, namely varieties Inpago and Sunggo, while the second factor is fertilizer input, double inoculant of P solubilizing bacteria + K solubilizing bacteria + N fixing bacteria, double inoculant of AMF + solubilizing bacteria K + N-fixing bacteria , and inorganic fertilizer recommended by AIAT, namely 200 kg Urea/ha, 100 kg SP36/ha, 100 kg KCl/ha. The two factors were combined so that there were 6 treatment combinations which were repeated 4 times so that there were 24 experimental units. Each experimental unit consists of 50 plants so that the total plant population was 50 x 24 = 1,200 plants. The results showed that the use of biological fertilizers in upland rice cultivation in coastal areas was able to increase the availability of N, P, and K nutrients compared to the initial soil and recommended fertilizers. Upland rice varieties suitable for coastal areas are Inpago 10 with fertilizer in the form of a combination of biofertilizers of Phosphate Solubilizing Bacteria + K Solvent Bacteria + N Fixing Bacteria.

Pristine soil property and mineralogy as the strategic rehabilitation basis in post-earthquake-induced liquefaction, tsunami and landslide in Palu, Indonesia

Unprecedented terrible and catastrophic disasters on September 28, 2018 triggered by earthquake-induced liquefaction, tsunami and landslide hit Palu, Central Sulawesi, Indonesia. The objective of the study was to assess and evaluate soil mineralogical compositions, properties, heavy metals, and water quality in the areas of post-earthquake-induced liquefaction, tsunami and landslide to provide the basis for agricultural and ecosystem rehabilitation. The soil samples were collected by digging pits after 12-days of disaster at liquefied soils, tsunami sediments, and soil mass motion/landslide for analyses. Water samples for analysis were collected from soil pits, surface flow and new spring. Results showed that the earthquake-induced liquefaction, tsunami and landslide completely reshape the ecosystem landscape and reset the initial soil formation as revealed by the formation of sand boil microrelief, accumulation of tsunami sediment on initial soil surfaces, and redistribution of soil through mass movement on landscapes. Liquefaction increased the number of weatherable minerals in the sand fraction, varying from 28 to 58% as compared to natural soils (17–42%), indicating the high nutrient reserve of pristine liquefied soils in the long-term. The clay minerals were dominated by smectite followed by illite and kaolinite and were not affected by earthquake impacts. The liquefaction increased soil pH and sand fraction and decreased all soil nutrients, which collectively became severe limiting factors for crop establishment. The tsunami resulted in new material deposits of 5–10 cm thick overlain the natural soils in coastal areas. The deposits did not increase the number of weatherable minerals but resulted in the highest electrical conductivity of soil and water, and high concentrations of Ca, Na, Mg and K ions. The concentration of total and availability of all types of heavy metals is below the threshold limits, indicating no potential heavy metal risks in post-earthquake-induced disaster areas. Information of high weatherable minerals and pristine soil properties, water and heavy metals from this study may provide a strong effective basis for rehabilitation and management of agriculture and the environment in post-disaster areas in the long-term period of time.

Effect of salinity on soil structure and soil hydraulic characteristics

Revealing the influences of soil salinity on soil structure and hydraulic properties contributes to understanding the mechanism of salinity restraining rehabilitation of saline sodic soil in coastal area. After being passed through a 1 mm sieve, silt loam and silty clay were irrigated with saline water to achieve different soil salinities to highlight the effect of irrigation salinity on aggregate formation from primary particles. Three irrigation events with different saline water were conducted in the same 2 mo interval in soil columns; the soil columns were subjected to natural evaporation during the interval. The soil salinity, soil structure, soil–water characteristic curve, and saturated hydraulic conductivity (Ks) results were determined after the end of the third drying subprocess. The results showed that the proportion of water-stable macroaggregates (0.25–2 mm) in the silt loam and silty clay increased as the soil salt content (SSC) increased. Under the same matric suction, the retention capacity and plant-available water capacity (PAWC) of the silt loam first increased and then decreased, with the SSC increasing to a maximum of approximately 14.5 g kg−1. The retention capacity of the silty clay increased with the SSC, whereas the PAWC decreased with the SSC. The Ksof the silt loam increased with SSC. This study reveals the effects of soil salinity on aggregate formation from primary particles in wetting–drying cycles and describes the corresponding changes in hydraulic properties, which influence the rehabilitation of saline sodic soils in coastal areas.

Triaxial behavior of cement-stabilized organic matter–disseminated sand

Organic matter–disseminated sand (OMDS) is a widely distributed problematic soil in coastal areas of Hainan province, China. Its existence makes the installation of piles difficult and has the risk of insufficient bearing capacity. OMDS is different from other organic soils such as peat in terms of formation, mineral component, organic content, and forms of organic matters. In this study, 20% (w/w) cement together with 7.5% (w/w) lime at a water–cement ratio of 0.45 was mixed with OMDS to improve its mechanical performances. A series of unconsolidated undrained static triaxial test was conducted on the stabilized OMDS to investigate the failure mode, stress–strain relationship, maximum and residue deviator stress, axial strain at failure, and elastic modulus under various confining pressures (0, 200, 300, 400 kPa) and curing time (7d, 14d, 28d). The test results showed that higher confining pressure and longer curing time in general led to higher maximum and residue deviator stress, larger axial strain at failure, and larger secant elastic modulus of cement-stabilized OMDS. The maximum and residue deviator stress of cement-stabilized OMDS increased with curing time and ranged from 500 to 2180 kPa and from 250 to 1800 kPa, respectively. Under elevated confining pressure, maximum deviator stress increased substantially, irrespective of curing time. Secant elastic modulus (E50) increased with confining pressure at these three curing time, from 29 to 42 MPa. Due to the existence of organic matters, the strength of cement-stabilized OMDS was lower than cement-stabilized non-organic sand, regardless of confining pressure and curing time. This study provided new insight into the shear strength behavior of cement-stabilized OMDS under different confining conditions. This will facilitate the design and construction of foundations in this type of soil.

Geochemical Study and Remedial Measures of Seawater Ingression in the Southern Part of Purba Medinipur District in West Bengal

There is a severe warning of groundwater pollution in the coastal district of Purba Medinipur, West Bengal. This is due to ingression of saline water intrusion. A top stratum of the soil in coastal area of the district is found to be made of different layer of clay and sand of sea origin. The groundwater cannot be used for domestic, irrigation or industrial purposes. As a result of continuous extraction of water, the groundwater is formed like a cone of depression. It has resulted in redundant well and therefore the water extraction has become uneconomical due to augmented lift. All these necessitate for urgent measures to control the ingression of salt water into the coastal aquifers. Some measures to control the encroachment of salt water are suggested in this paper.

Accumulation and ecological risk of heavy metals in soils along the coastal areas of the Bohai Sea and the Yellow Sea: A comparative study of China and South Korea

Soils in coastal areas of the land-sea interface are vulnerable to heavy metal (HM) accumulation and subsequently to human health risk. However, few studies have investigated the HM pollution and risk in soils along the coastal areas of the Yellow Sea Large Marine Ecosystem (YSLME), in an international perspective. This study is the first comprehensive work in the YSLME encompassing 122 coastal locations along the Bohai Sea (BS), Yellow Sea of China (YSC), and Yellow Sea of South Korea (YSK). Soil HM pollution showed great spatial variations cross the regions and countries. Accumulations of As, Cu, Pb, and Zn in the YSK were significantly higher than those in the BS and YSC (p < 0.05). Whilst the elevated Cd, Hg, and Ni in soils were found in the BS and YSC compared to those in the YSK (p < 0.05). Meantime, the assessment of ecological risk posed by HMs indicated higher potential risk in the BS than other coastal areas. In specific, Cd and Hg posed a higher risk in the BS and YSC, while As showed relatively high risk in the YSK, indicating site-dependent accumulation of HMs in soils. Soil pH and organic matter were found to be important factors affecting the HM accumulation in the study areas. Industrial activities are the major driving factors influencing spatial distributions of HMs, and such activities exhibited different degrees of influence across the sampling sites. Altogether, the results of present study first identified the bilateral characteristics of soil HM pollution along the entire coasts of the YSLME in a comprehensive manner in several aspects: (1) sources, (2) hot spots, (3) priority chemicals of concern, and (4) site-specific potential risk of the soil HMs. Overall, this study provides references and backgrounds for future environmental management strategies and aids in developing a bilateral government policy towards coastal pollution management of HMs from an international scale and perspective.

Effect of high salinity in grout on the performance of cement-stabilized marine clay

Constructing a soilcrete column by injecting grout into the soil is a common method of stabilizing loose soil in coastal areas. Although tap water usually is used in the grout mixture for soil improvement projects, before the cement in grout mixture has completely set, tap water will mix with in situ saline seawater. Researchers have not previously considered the behavior of clay-cement under marine conditions, especially the effect of water salinity, on the performance of soilcrete. The goals of this study were to investigate the effect of the use of naturally saline seawater in grout preparation on the mechanical, physical and microstructural behavior of cement-stabilized marine clay. Marine clay and seawater samples were prepared along the northern shore of the Persian Gulf. Tap water as low salinity water, brackish water as medium salinity water (50% tap water and 50% seawater) and natural seawater as high salinity water were used. Specimens were prepared using the deep mixing method recommendations for laboratory soilcrete tests. Macroscopic evaluation was performed by unconfined compressive strength and indirect Brazilian tension test. The physical aspects of the plasticity of the soilcrete specimens with regard to the Atterberg limits and changes in the particle size distribution caused by cement bonding were evaluated by hydrometer testing. For the micromechanical study, SEM images were prepared from selected specimens. The results show that the use of natural seawater does not reduce the strength in comparison with tap water. Specimens containing brackish water (50% seawater and 50% tap water) showed maximum strength due to flocculation in the structure of the clayey cluster in comparison with tap water. The compressive strength ranged from 1.5 to 5 MPa for clay-cement specimens made of natural soil and seawater. The ratio of tensile strength to compressive strength of these specimens was 0.15–0.25. The results show that the unconfined compressive strength of soilcrete specimens constructed under field conditions was 30% that of specimens constructed under laboratory conditions.