Liquefaction susceptibility and deformation characteristics of saturated coral sandy soils subjected to cyclic loadings-a critical review

Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.

Bentonite-humic acid improves soil organic carbon,microbial biomass,enzyme activities and grain quality in a sandy soil cropped to maize(Zea mays L.) in a semi-arid region

A bentonite-humic acid(B-HA) mixture added to degraded soils may improve soil physical and hydraulic properties, due to effects such as improved soil structure and increased water and nutrient retention, but its effect on soil physicochemical and biological properties, and grain quality is largely unknown. The effect of B-HA, added at 30 Mg ha^(-1), was studied at 1,3, 5 and 7 years after its addition to a degraded sandy soil in a semi-arid region of China. The addition of B-HA significantly increased water-filled pore space and soil organic carbon, especially at 3 to 5 years after its soil addition to the soil. Amending the sandy soil with B-HA also increased the content of microbial biomass(MB)-carbon,-nitrogen and-phosphorus, and the activities of urease, invertase, catalase and alkaline phosphatase. The significant effect of maize(Zea mays L.) growth stage on soil MB and enzyme activities accounted for 58 and 84% of their total variation, respectively. In comparison, B-HA accounted for 8% of the total variability for each of the same two variables. B-HA significantly enhanced soil properties and the uptake of N and P by maize in semi-arid areas. The use of B-HA product would be an effective management strategy to reclaim degraded sandy soils and foster sustainable agriculture production in northeast China and regions of the world with similar soils and climate.

Effects of Carboxymethylcelluloses (CMC) on Some Hydraulic Properties of Sandy Soil

The property of hydrophilic polymers capable absorbing huge volumes of water led to many practical applications of these new materials in arid regions for improving the water retention in sandy soils. Effects of four carboxymethylcelluloses (CMC), mixed at various rates with the sandy soil, on the water-holding capacity and hydraulic conductivity (KS ) when leached with distilled water (simulating rain), tap water, and saline water were evaluated. The maximum water absorption of CMCs ranged between 80 and 100 kg ? kg-1 of polymer; however, the absorbent swelling capacity decreased significantly with increasing the salt concentration in the solution. The water absorption capacity of CMCs decreased significantly when incorporated in the sandy soil compared to that of the absorbent alone. Application of CMC increased significantly the available water content up to 3 ± 0.5 times. All soils treated with CMCs showed a significant lower in KS compared to the control soil. Meanwhile, KS was found increased with increasing the salt concentration in the leaching solution. This understanding of characteristics of the absorbents and the interactions among absorbents, soil, and irrigation water quality would be of help in water management of sandy soil.

Aggregate sizes regulate the microbial community patterns in sandy soil profile

Soil microorganisms play a key role in the function of soil ecosystem,yet our knowledge about how microbial communities respond to the typically sandy soil environmental properties along the soil profile is still insufficient.We investigated the soil microbial community patterns from top(0–20 cm)to clay-layer(>80 cm)of the typical sandy soils in three regions in China with different levels of precipitation,including Lishu County in Jilin Province(LS),Langfang City in Hebei Province(LF)and Zhengzhou City in Henan Province(ZZ).Our findings showed that small-size aggregates(<0.5 mm)rather than large ones(³0.5 mm)dominated the soil profile.The relative abundances of Actinobacteria,Crenarchaeota and Firmicutes were highly related to aggregate proportions of the deep clay-layer soil.The network analysis revealed the distinct community patterns among modules,evidencing niche differentiation along the soil profile.The keystone species OTU_11292 was observed having migrated clearly into the other module of the clay-layer soil.Different roles of the OTU_30(belonging to Gemmatimonadetes)in soil processes might partly explain the different microbial distribution between top-and clay-layer soils.These findings provided new insights into the candidate mechanisms of microbial diversity maintenance and community patterning of sandy soils,which were necessary for better understanding of ecological rules guiding long-term agricultural practice.

Continuous cropping of alfalfa (Medicago sativa L.) reduces bacterial diversity and simplifies cooccurrence networks in aeolian sandy soil

Alfalfa is a perennial herbaceous forage legume that is remarkably and negatively affected by monocropping.However,the contribution of the changes in bacterial communities to soil sickness in alfalfa have not been elucidated.Therefore,we investigated bacterial community structures in response to monocropped alfalfa along the chronosequence.Continuous cropping remarkably reduced bacterial alpha diversity and altered community structures,and soil pH,total P and available P were strongly associated with the changes of bacterial diversity and community structures.Intriguingly,10 years of monocropped alfalfa might be a demarcation point separating soil bacterial community structures into two obvious groups that containing soil samples collected in less and more than 10 years.The relative abundances of copiotrophic bacteria of Actinobacteria and Gammaproteobacteria significantly increased with the extension of continuous cropping years,while the oligotrophic bacteria of Armatimonadetes,Chloroflexi,Firmicutes and Gemmatimonadetes showed the opposite changing patterns.Among those altered phyla,Actinobacteria,Chloroflexi,Alphaproteobacteria and Acidobacteria were the most important bacteria which contributed 50.86%of the community variations. Additionally, the relative abundances of nitrogen fixation bacteria ofBradyrhizobium and Mesorhizobium obviously increased with continuous cropping years, while theabundances of Arthrobacter, Bacillus, Burkholderiaceae and Microbacterium with potential functionsof solubilizing phosphorus and potassium remarkably decreased after long-term continuouscropping. Furthermore, bacterial cooccurrence patterns were significantly influenced by continuouscropping years, with long-term monocropped alfalfa simplifying the complexity of the cooccurrencenetworks. These findings enhanced our understandings and provided references for forecasting howsoil bacterial communities responds to monocropped alfalfa.

Effect of irrigation water containing arsenic on elemental composition of bean and lettuce plants cultivated in calcareous sandy soil

Background:The uptake of arsenic by vegetables from soil irrigated with arsenic enriched groundwater poses a major health hazard.The edible portion of these vegetables transfer arsenic to the human beings.The uptake of arsenic was studied in bean(Phaseolus vulgaris L.)and lettuce(Lactuca sativa L.)in a controlled greenhouse pot culture with calcareous sandy soil as substrate.The plants were irrigated with water containing sodium arsenate at concentrations 0.1,0.25 and 0.5 mg L^(-1).The total arsenic concentration of the different plants parts was determined by ICP-MS,following microwave-assisted acid digestion.The change in plant biomass production and essential macroelements(Mg,P,K)and microelements concentration(Fe,Mn,Cu,Zn)was also studied.Results:The As concentration in the bean was in the order:root>stem>leaf>bean fruit and in lettuce:root>leaves.At the highest dose(0.5 mg L^(-1))the As concentration in the bean fruit and lettuce leaves was 22.1μg kg^(-1)and 1207.5μg kg^(-1)DW,respectively.Increasing As concentration in the irrigation water resulted in decreased edible biomass production in bean,while in lettuce the edible biomass production increased.Neither plant exhibited any visible toxicity symptoms.No significant change was observed in the macro and microelements concentration.The total and the water-soluble arsenic in soil amounted to 3.5 mg kg^(−1)and 0.023 mg kg^(−1),respectively.The transfer factor was found to increase with increase in the As treatment applied.The transfer factor range for bean from root to fruit was 0.003–0.005,and for lettuce from root to leaves was 0.14–0.24.Conclusion:Considering the FAO-WHO recommended maximum tolerable daily intake(MTDI)limit of 2.1μg kg^(-1)body weight,and the biomass production,both plants should not be cultivated at As treatment level higher than 0.1 mg L^(-1).

Cogon grass biochar amendment and Panicum coloratum planting improve selected properties of sandy soil under humid lowland tropical climatic conditions

Biochar amendment improves the physical,chemical and biological characteristics of different soil types under different climatic and environmental conditions.In this study,effects of biochar or live pasture plants existing alone or co-existing on selected soil properties of sandy loam soil under humid lowland tropical climatic conditions were investigated.The changes measured in the amended soil,with or without plants,were compared to the unamended and unplanted soils.Biochar amendment with or without pasture improved moisture retention,lowered bulk density,increased pH and kept the electrical conductivity within ranges conducive for pasture growth.Generally,contents of all the nutrients increased following biochar amendment,however pasture establishment without amendment resulted in depletion of available potassium and magnesium.Under all treatment conditions,soil organic carbon and soil organic matter were significantly depleted.Cogon grass is invasive under all land use systems and contributes to greenhouse gas emissions through slash-and-burn.Using biomass from the grass instead of burning would mitigate CO2 emissions from the tropics.

Response of plant physiological parameters to soil water availability during prolonged drought is affected by soil texture

Soil water deficit is increasingly threatening the sustainable vegetation restoration and ecological construction on the Loess Plateau of China due to the climate warming and human activities.To determine the response thresholds of Amygdalus pedunculata(AP)and Salix psammophila(SP)to soil water availability under different textural soils,we measured the changes in net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),leaf water potential(ψw),water use efficiency(WUE)and daily transpiration rate(Td)of the two plant species during soil water content(SWC)decreased from 100%field capacity(FC)to 20%FC in the sandy and loamy soils on the Loess Plateau in the growing season from June to August in 2018.Results showed that Pn,Gs,WUE and Td of AP and SP remained relatively constant at the beginning of soil water deficit but decreased rapidly as plant available soil water content(PASWC)fell below the threshold values in both the sandy and loamy soils.The PASWC thresholds corresponding to Pn,Gs and Ci of AP in the loamy soil(0.61,0.62 and 0.70,respectively)were lower than those in the sandy soil(0.70,0.63 and 0.75,respectively),whereas the PASWC thresholds corresponding to Pn,Gs and Ci of SP in the loamy soil(0.63,0.68 and 0.78,respectively)were higher than those in the sandy soil(0.58,0.62 and 0.66,respectively).In addition,the PASWC thresholds in relation to Td and WUE of AP(0.60 and 0.58,respectively)and SP(0.62 and 0.60,respectively)in the loamy soil were higher than the corresponding PASWC thresholds of AP(0.58 and 0.52,respectively)and SP(0.55 and 0.56,respectively)in the sandy soil.Furthermore,the PASWC thresholds for the instantaneous gas exchange parameters(e.g.,Pn and Gs)at the transient scale were higher than the thresholds for the parameters(e.g.,Td)at the daily scale.Our study demonstrates that different plant species and/or different physiological parameters exhibit different thresholds of PASWC and that the thresholds are affected by soil texture.The result can provide guidance for the rational allocation and sustainable management of reforestation species under different soil conditions in the loess regions.

Calibration method of mesoscopic parameter in sandy cobble soil triaxial test based on PFC3D

This paper presents a rapid and effective calibration method of mesoscopic parameters of a threedimensional particle flow code(PFC3D)model for sandy cobble soil.The method is based on a series of numerical tests and takes into account the significant influence of mesoscopic parameters on macroscopic parameters.First,numerical simulations are conducted,with five implementation steps.Then,the multi-factor analysis of variance method is used to analyze the experimental results,the mesoscopic parameters with significant influence on the macroscopic response are singled out,and their linear relations to macroscopic responses are estimated by multiple linear regression.Finally,the parameter calibration problem is transformed into a multi-objective function optimization problem.Numerical simulation results are in good agreement with laboratory results both qualitatively and quantitatively.The results of this study can provide a basis for the calibration of microscopic parameters for the investigation of sandy cobble soil mechanical behavior.

Characteristic Test Study on Bearing Capacity of Suction Caisson Foundation Under Vertical Load

Suction caisson foundations are often subjected to vertical uplift loads,but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisson foundation.So it is important to establish an uplift failure criterion.In order to study the uplift bearing mechanism and failure mode of suction caisson foundation,a series of model tests were carried out considering the effects of aspect ratio,soil permeability and loading mode.Test results indicate that the residual negative pressure at the top of caisson is beneficial to enhance uplift bearing capacity.The smaller the permeability coefficient is,the higher the residual negative pressure will be.And the residual negative pressure is approximately equal to the water head that causes seepage in the caisson.When the load reaches the ultimate bearing capacity,both the top and bottom negative pressures are smaller than Su and both the top and bottom reverse bearing capacity factors are smaller than 1.0 in soft clay.Combined the uplift bearing characteristics of caisson in sandy soil and soft clay,the bearing capacity composition and the calculation method are proposed.It can provide a reference for the engineering design of suction caisson foundation under vertical load.

A new empirical equation of shear wave velocity to predict the different peak surface accelerations for Jakarta city

Site condition and bedrock depth play important roles in the determination of peak surface acceleration(PSA)values by earthquake motions.The soil parameters of shear wave velocity(Vs)and standard penetration test-number(N)value for Jakarta city are available up to 100 m below the Earth’s surface even though the typical depths to bedrock are in excess of 100 m.This study referred to the base motion peak ground acceleration(PGA)values of 0.100 g,0.218 g and 0.378 g to predict the PSA values using the Nonlinear Earthquake site Response Analysis(NERA)to analyse a simulated dataset for the bedrock depths of 100 m,200 m,300 m,400 m and 500 m with conditioned by clayey and sandy soils.A new empirical equation of Vs=102.48 N0.297(m/s)was proposed to calculate the values of Vsused as an input parameter in the NERA programme for the prediction of seismic wave propagation.The results showed that the PSA values are dependent on the amplitude of seismic waves,depths of bedrock and the local site conditions.Changes in the PSA values from 41.0%to 51.5%and from 46.1%to 79.8%for the bedrocks overlain by sand,from 20.0%to 42.1%and from 45.9%to 58.8%for the bedrocks overlain by clay with increasing of bedrock depths from 200 m to 300 m and from 400 m to 500 m,respectively,were predicted for a 2500-year return period earthquake.Decreases in the PSA values by 41.0%,51.5%,46.1%,79.8%for the bedrocks overlain by sand and by 20.0%,42.1%,45.9%,58.8%for the bedrocks overlain by clay were predicted for a 2500-year return period earthquake due to the bedrock depth changes of 200 m,300 m,400 m,500 m.Large-magnitude earthquake of Jakarta city has a significant effect on an increase or a decrease of the PSA value with depth of bedrock and may cause the vibration damage to buildings and other constructions on the ground.The analysis of the PSA value and PSA ratio influenced by the PGA value,bedrock depth and local soil conditions will make a contribution to the design of earthquake-safe building for Jakarta city in the future.

Water Consumption and Maize Yield for Alternative Furrow Irrigation in Western Heilongjiang Province

Aiming at less and un-uniform distribution rainfall problems, the serious draught in spring, low crop production and water efficiency in sandy soil area of Heilongjiang Province, the experiment of alternative furrow irrigation was conducted in Dumeng County in 2009. The purpose of the experiment was to find the water consumption law and its influence on maize yield. The results showed that the highest water consumption was during the heading stage and the highest daily consumption of water was during the filling stage. The stimulation effect of alternative furrow irrigation on yield was obvious in the appropriate irrigation level. The best irrigation pattern for the highest yield was as follows: the seedling stage was 325 m3 ? hm-2; the jointing stage was 400 m3 ? hm-2; and the filling stage was 288 m3 ? hm-2. The water consumption during each growing period was that the seedling was 38.85 mm; the jointing was 108.11 mm; the heading was 124.39 mm; the filling was 88.96 mm; the milk was 60.21 mm; and the harvesting was 47.89 mm.

Separation and mechanical properties of residual film and soil

In Xinjiang's perennial cotton(Gossypium hirsutum)-planting soil,the average residual amount of plastic film is as high as 265.3 kg/hm2,and the problem of pollution with residual plastic film in the tillage layer has become a major problem.To explore the mechanism of the separation of residual film and soil in the tillage layer and determine the conditions favorable for the separation of residual film-soil,this study established a constitutive model of residual film-soil contact based on the discrete element method and used the established constitutive model to simulate the process of separating residual film and soil.In addition,the influence of parameters,such as soil particle size and water content,on the force to separate the residual film and soil was studied using single factor and orthogonal experiments.The simulation results showed that the changing trend of the residual film-soil separation force curve did not differ much between the simulation and the actual comparison,and the curves were roughly the same.They all decreased after the separation force reached its peak value,but the simulated separation force curve was similar to that of the actual separation force.It increased rapidly from the beginning and reached peak separation force first.The single-factor experiment showed that the separation force of the used residual mulching film was higher than that of the unused mulching film.Under the same conditions,the maximum separation force required to separate the residual membrane was proportional to the positive pressure on the surface of the residual membrane and the size of soil particles.Under the same conditions,the maximum separation force required to separate the residual film is proportional to the positive pressure on the surface of the residual film and the size of soil particles.The maximum separation force decreased first and then increased as the soil moisture content increased.The results of the orthogonal experiment showed that the soil particle size had the greatest effect on the maximum separation force,followed by positive pressure on the residual film surface,soil moisture content,and the service life of mulch.In addition,film mulch that was buried 60 mm deep in the soil,a particle size of more than 2.5 mm,and a soil moisture content of 8%was the optimal combination of parameters to effectively separate the film mulching residue from the soil.

A Comprehensive Study on the Consequences of Gap-Graded Sands Considering the Loss of Fine Particles

Water and sand leakage disasters are likely to occur during construction in water-rich sand layer areas,resulting in ground collapse.The stress-strain action characteristics of discontinuous graded sand under different internal erosion degrees,and the evolution mechanism of water and sand leakage disasters caused by the internal erosion need to be further explored.Therefore,this paper takes the discontinuous graded sand in a water rich sand layer area in Nanchang City of China as the research object.Considering the influence of different fine particle losses(0,10%,20%and 30%)under the internal erosion of sand,the salt solution method is used to realize the specified loss of fine particles in the internal erosion.The stress-strain behavior after the loss of fine particles due to internal erosion is studied by triaxial shear test.Meanwhile,the physical model test and PFC-CFD method are both used to study the evolution rules of water and sand leakage disaster considered the influence of internal erosion degrees.Results show that:(1)under the same confining pressure,the peak failure strength of sand samples decreases along with the increase of fine particle loss.(2)In the water and sand leakage test of saturated sand,a natural filter channel is formed above the observed soil arch.The greater the loss of fine particles,the steeper and wider the collapse settlement area.(3)The relationship between the cumulative amount of water and sand leakage and time is nonlinear.The total mass loss of sand increases along with the increase of internal erosion degree.(4)After the soil arch is formed around the damaged opening,the sand continues to converge above the soil arch under the action of water flow,resulting in the dense convergence of contact force chains.

Biotreatment of incinerated bottom ash and biocementation of sand blocks using soybean urease

Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.

Temperature sensitivity of soil organic matter decomposition varies with biochar application and soil type

Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide(CO2) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar(0, 6.25, 12.5, and 25 Mg ha-1) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40℃. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO2 emissions when compared to untreated soils;ii) CO2 emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils;iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils;and iv) for clay soils, relative increases in soil CO2 emissions from biochar-amended soils were higher when the temperature increased from 30 to 40℃, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30℃. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil-and weather-specific timing of biochar application.

Sugarcane bagasse amendment mitigates nutrient leaching from a mineral soil under tropical conditions

Large quantities of organic by-products are generated by the sugarcane industry during sugar extraction process.These by-products may be used as soil amendments to improve soil quality,as nutrient leaching is common in mineral soils of Florida in USA due to their sandy texture and frequent rain events.A soil column study was designed to evaluate the effects of bagasse application at 85 t ha^(-1) of fresh bagasse,170 t ha^(-1) of fresh bagasse,and 170 t ha^(-1) of fresh bagasse+nitrogen(N)on the leaching potential of carbon(C),N,phosphorus(P),and potassium(K).Bagasse was incorporated within the topsoil(0-15 cm)in outdoor soil columns exposed to natural conditions,with periodical irrigation during the experiment.After approximately 57 weeks,the distributions of C,N,P,and K were evaluated at three soil depths(i.e.,0-15,15-30,and 30-53 cm)within the soil columns.Total organic C(TOC),N,and P in leachates decreased significantly from the soils amended with bagasse compared with the control with no bagasse and no N.Based on K content changes in the columns,bagasse could also be utilized as a potential source of K for plants.Overall,application of bagasse as a soil amendment might be an effective way to sustainably reutilize organic by-products while reducing concerns regarding major nutrients entering groundwater resources.The results of this study could assist in developing nutrient management plans of using sugarcane bagasse as a potential soil amendment in mineral soils.

Distribution of 137Cs and 60Co in plough layer of farmland: Evidenced from a lysimeter experiment using undisturbed soil columns

Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant(NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment(800 d), >96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils;very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth(25 cm) in both soils. Three phases on the vertical migration rate(v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement(0–355 d, v = 219 ± 17 mm year-1), followed by a steady movement(355–577 d, v = 150 ± 24 mm year-1) and a very slow movement(577–800 d, v = 107 ± 7 mm year-1). In contrast, its migration rate in the brown soil(v = 133 ± 17 mm year-1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon(SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer(0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface(20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades.Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.

Assessment of glass fiber-reinforced polyester pipe powder in soil improvement

This study investigates the use of glass fiber-reinforced polyester(GRP)pipe powder(PP)for improving the bearing capacity of sandy soils.After a series of direct share tests,the optimum PP addition for improving the bearing capacity of soils was found to be 12%.Then,using the optimum PP addition,the bearing capacity of the soil was estimated through a series of loading tests on a shallow foundation model placed in a test box.The bearing capacity of sandy soil was improved by up to 30.7%.The ratio of the depth of the PP-reinforced soil to the diameter of the foundation model(H/D)of 1.25 could sufficiently strengthen sandy soil when the optimum PP ratio was used.Microstructural analyses showed that the increase in the bearing capacity can be attributed to the chopped fibers in the PP and their multiaxial distribution in the soil.Besides improving the engineering properties of soils,using PP as an additive in soils would reduce the accumulation of the industrial waste,thus providing a twofold benefit.

Monitoring the variation of soil quality with sewage sludge application rates in absence of rhizosphere effect

Agricultural soils in semi-arid regions have frequently been degraded due to adverse climatic conditions,organic matter depletion,and poor farming practices.To enhance soil quality,this study examines the reuse of sewage sludge(SS)as an available source of organic matter in a typical Mediterranean sandy-loam soil.Accordingly,we studied the cumulative effect of two annual applications of 40,80 and 120 tons of sludge per ha on soil quality in absence of vegetation.The dose-dependent improvement of organic matter content was the most significant event that reflected sludge application rates,and consequently influenced other soil properties.Accordingly,soil structural stability increased by 13.3%,28.8%and 59.4%for treatments SS-40,SS-80 and SS-120 respectively as compared to unamended control.Structural stability improvement was also confirmed by the dose-dependent variation of other edaphic factors including calcium content,the microbial quotient as well as Welt and C:N ratios.These param-eters are involved in cementing soil aggregates by cation bridging,the formation of microbial mucilage,and clay-humic complexes.Soil magnetic susceptibility(SMS)was measured in situ as a possible rapid tool to evaluate soil condition.SMS showed significant correlation with sludge dose and stability amelioration testifying to the aggregation role that can play Al2O3 and particularly Fe2O3 minerals added by the hematite-rich sludge.Besides,analytical results and field observations revealed no trends of soil salinization or acidification by excessive sludge amounts.By avoiding the rhizosphere effect,outcomes could reflect the resilience and intrinsic capacity of the soil to cope with excessive sludge loads.