Both physical and chemical processes affect the fate and transport of herbicides. It is useful to simulate these processes with computer programs to predict solute movement. Simulations were run with HYDRUS- 1 D to id...Both physical and chemical processes affect the fate and transport of herbicides. It is useful to simulate these processes with computer programs to predict solute movement. Simulations were run with HYDRUS- 1 D to identify the sorption and degradation parameters of atrazine through calibration from the breakthrough curves （BTCs）. Data from undisturbed and disturbed soil column experiments were compared and analyzed using the dual-porosity model. The study results show that the values of dispersivity are slightly lower in disturbed columns, suggesting that the more heterogeneous the structure is, the higher the dispersivity. Sorption parameters also show slight variability, which is attributed to the differences in soil properties, experimental conditions and methods, or other ecological factors. For both of the columns, the degradation rates were similar. Potassium bromide was used as a conservative non-reactive tracer to characterize the water movement in columns. Atrazine BTCs exhibited significant tailing and asymmetry, indicating non-equilibrium sorption during solute transport. The dual-porosity model was verified to best fit the BTCs of the column experiments. Greater or lesser concentration of atrazine spreading to the bottom of the columns indicated risk of groundwater contamination. Overall, HYDRUS-1D successfully simulated the atrazine transport in soil columns.展开更多
The principle and process of parallel seismic (PS) testing for the integrity testing of cemented soil columns are in- troduced in this paper. A three-dimensional (3D) finite element model (FEM) for the pile-soil syste...The principle and process of parallel seismic (PS) testing for the integrity testing of cemented soil columns are in- troduced in this paper. A three-dimensional (3D) finite element model (FEM) for the pile-soil system is established for impulse responses. Under saturated soil or unsaturated soil condition, several vibrating velocity-time histories at different depths in parallel hole are obtained based on the numerical simulation. It shows that the length of the pile and the one-dimensional (1D) P-wave velocity in the pile can be determined easily from the features of the mentioned velocity-time histories. By examining the slopes of the first arrival time plotted versus depth or the depth where the amplitude of the first arrival significantly decreases, the length of the pile can be determined. The effects of the 3D P-wave propagation through the saturated soil and the defect of the cemented soil column on the velocity-time histories are also investigated.展开更多
The adsorption and desorption coefficients of atrazine, methiocarb and simazine on a sandy loam soil were measured in this study with soil column liquid chromatographic (SCLC) technique. The adsorption and desorption ...The adsorption and desorption coefficients of atrazine, methiocarb and simazine on a sandy loam soil were measured in this study with soil column liquid chromatographic (SCLC) technique. The adsorption and desorption data of all the three pesticides followed Freundlich isotherms revealing the existence of hysteresis. In comparing with other methods, SCLC method showed some characteristics such as rapidity, online and accuracy.展开更多
Soil column liquid chromatography (SCLC) was developed to determine soil organic carbon adsorption coefficients (E-oc) for chemicals. The uptake by soil of pesticides from water can be conveniently calculated from the...Soil column liquid chromatography (SCLC) was developed to determine soil organic carbon adsorption coefficients (E-oc) for chemicals. The uptake by soil of pesticides from water can be conveniently calculated from the related breakthrough curves (BTC). The nine pesticides chosen for determination in this study are soluble ones, with their water solubility ranging from 62 mg/L to Z mg/L. In comparing with existing methods of K-oc, SCLC possesses rapid, online and accurate characteristics.展开更多
Metam sodium （MS; sodium N-methyl dithiocarbamate） has emerged as a promising soil fumigant in the US to replace methyl bromide （MeBr）. Metam potassium （MK; potassium N-methyl dithiocarbamate） and MS break down ...Metam sodium （MS; sodium N-methyl dithiocarbamate） has emerged as a promising soil fumigant in the US to replace methyl bromide （MeBr）. Metam potassium （MK; potassium N-methyl dithiocarbamate） and MS break down into the volatile gas methyl isothiocyanate （MITC） to control soil borne pests. Many studies have focused on MS, but MK has not been studied as thoroughly. The objective of this research was to determine the effect of increasing organic matter （OM） treatments and soil texture to minimize the off-gassing of MS and MK. Bench-scale soil column studies were performed to simulate organic matter treatments that may decrease the volatilization loss of MITC. Incorporation depth of OM simulated surface tillage （0-15 cm） practices. Soil was packed in steel columns and MS or MK was applied at a depth of 15 cm and MITC volatilization was measured using gas chromatography/mass spectroscopy. Volatilization of MITC behaved similarly for MS and MK with MITC movement impacted by soil texture. MITC volatilization was lower from a sandy clay loam than a sandy soil. Surface incorporation of OM did not significantly decrease MITC volatilization. These results suggest that soil texture is the dominant factor reducing MITC off-gassing and prolonging the time needed to control soil borne pests.展开更多
The riverbank soil is a natural purifying agent for the polluted river water(Riverbank filtration, RBF). This is of great importance to groundwater safety along the riverbank. This paper examines the migration and tra...The riverbank soil is a natural purifying agent for the polluted river water(Riverbank filtration, RBF). This is of great importance to groundwater safety along the riverbank. This paper examines the migration and transformation rules of ammonia-nitrogen in three typical types of sand soil using the indoor leaching experiment of soil column, and then makes comparison with the indoor experiment results in combination with the numerical simulation method. The experiment process shows that the change in ammonia-nitrogen concentration goes through three stages including "removal-water saturation-saturation". As the contents of clay particles in soil sample increase, the removal of ammonia-nitrogen from soil sample will take more time and gain higher ratio. During the removal period, the removal ratio of Column 1, Column 2 and Column 3 averages 68.8%(1-12 d), 74.6%(1-22 d) and 91.1%(1-26 d). The ammonia-nitrogen removal ratio shows no noticeable change as the depth of soil columns varies. But it is found that the ammonia-nitrogen removal ratio is the least of the whole experiment when the soil columns are at the depth of 15 cm. It can be preliminary inferred that the natural purifying performance of soil along the river for ammonia-nitrogen in river water mainly depends on the proportion of fine particles in soil. HYDRUS-1D model is used to simulate this experiment process, analyze the change of the bottom observation holes by time and depth in three columns(the tenth day), and make comparison with the experiment result. The coefficients of determination for fitting curves of Column 1, Column 2 and Column 3 are 0.953, 0.909, 0.882 and 0.955, 0.740, 0.980 separately. Besides, this paper examines the contribution of absorption, mineralization and nitrification in the simulation process. In the early removal stage, mineralization plays a dominant role and the maximum contribution rate of mineralization is 99%. As time goes by, absorption starts to function and gradually assumes a dominant position. In the middle and late removal stage, nitrification in Column 1 and Column 2 makes more contribution than mineralization. So the experiment result of the ammonia-nitrogen concentration is 0.6% and 2.4% lower than that in effluent and the maximum contribution ratio of nitrification is -4.53% and -5.10% respectively when only the function of absorption is considered. The mineralization in Column 1 and Column 2 in the middle and late removal stage still plays a more important role than nitrification. So the experiment result is 1.4% higher than that in effluent and the maximum contribution ratio of nitrification is -2.51% when only the function of absorption is considered. Therefore, absorption, mineralization and nitrification make different contributions during different part of the stage. This means that the natural purifying performance of soil along the river for ammonia-nitrogen in river water not only depends on the proportion of fine particles in soil, but depends on the mineralization and nitrification environment. This can offer some insights into the protection and recovery of groundwater along the riverbank.展开更多
Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied us...Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter × 28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures： Lyallpur soil series, clay loam （fine-silty, mixed, hyperthermic Ustalfic Haplargid）, and Sultanpur soil series, sandy loam （coarse-silty, mixed, hyperthermic Ustollic Camborthid）. The adsorption isotherms were developed by equilibrating soil with 0.01 tool L^-1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end of the leaching experiment, 0.11 L 10 g L^-1 blue dye solution was also applied to each column to mark the flow paths. The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio （the concentration in solution at equilibrium/concentration applied） was lower than that in the Sultanpur soil columns. The breakthrough of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications for the nutrient management in field soils.展开更多
Geosynthetics and deep cement mixed(DCM)soil columns have been widely used to improve soft soil grounds in many countries and regions.This paper presents an experimental study on a geosynthetic-reinforced sand fill ov...Geosynthetics and deep cement mixed(DCM)soil columns have been widely used to improve soft soil grounds in many countries and regions.This paper presents an experimental study on a geosynthetic-reinforced sand fill over marine clay with or without DCM columns under different loadings.Two tests were conducted on the sand fill reinforced with fixed-end and free-end geosynthetics over marine clay under three-stage local loading to investigate the effects of the boundary conditions of geosynthetic reinforcement on reducing settlements.It is observed that the fixed-end geosynthetic sheet is more effective in reducing settlements than the free-end condition under identical local loading.Another test was conducted on the fixed-end geosynthetic-reinforced sand fill over the marine clay improved by DCM columns under single-stage uniform loading.The vertical stresses on the marine clay and on the DCM columns,as well as the tensile strains of the geosynthetic sheet in the overlying sand fill,were measured.The results revealed that the stress concentration ratio increases with an increase in consolidation settlements,and the maximum tensile strain of the geosynthetic sheet occurs near the edge rather than at the center of the top surface of the DCM columns.展开更多
The combined application of mineral fertilizer and biochar significantly improves the passivation of heavy metal-contaminated soil,surpassing the effects of individual application.This study has reinforced the validat...The combined application of mineral fertilizer and biochar significantly improves the passivation of heavy metal-contaminated soil,surpassing the effects of individual application.This study has reinforced the validation of their passivation competence as soil remediation agents by examining the multifaceted role of potassium-silicon-calcium mineral fertilizer combined with rice husk-based biochar generated at different pyrolysis temperatures.The soil leaching column experiment,conducted based on the adsorption experiments,has facilitated our scrutiny of the passivation impacts of cadmium(Cd)and lead(Pb)when introducing different proportions of mineral fertilizers and biochar into the soil.These results indicate that biochar’s adsorption efficiency for Cd and Pb is significantly improved at escalated pyrolytic temperature conditions in a single solution.The biochar generated at 700℃(C700)renders adsorption effectiveness of approximately 84.24%for Cd and 99.74%for Pb.Biochar conspicuously registers superior adsorption efficiency towards Pb relative to Cd.The mineral fertilizer,which achieves an adsorption efficiency of 97.76%for Cd,is identified as the main adsorbent for Cd,although its competence is slightly lower compared to C700 for Pb adsorption.Within a complex solution,biochar and mineral fertilizer show reduced Cd and Pb adsorption levels compared to single solutions.There is a keen competition for adsorption surfaces witnessed between Cd and Pb,with Pb’s distribution coefficient(Kd)notably outpacing that of Cd.The isothermal adsorption analyses depict that the mineral fertilizer follows the Langmuir model for Cd adsorption,while C700 conveys the Freundlich model for Pb adsorption.The soil leaching column experiment’s results signify that the composite passivation agents significantly outperform the individual passivation agents in efficiency.The combined application of biochar and mineral fertilizer minimizes the cumulative leaching of Cd and Pb,with the optimal soil remedy proportion for heavy metal contamination being 7∶3.In practical application,mindful consideration should be accorded to the deployment ratios of different passivation agents.展开更多
The objective of this study is to develop an analytical methodology to evaluate the effectiveness of vibro stone column (S.C.) and dynamic compaction (D.C.) techniques supplemented with wick drains to densify and miti...The objective of this study is to develop an analytical methodology to evaluate the effectiveness of vibro stone column (S.C.) and dynamic compaction (D.C.) techniques supplemented with wick drains to densify and mitigate liquefaction in saturated sands and non-plastic silty soils. It includes the following: (i) develop numerical models to simulate and analyze soil densitication during S.C. installation and D.C. process, and (ii) identify parameters controlling post-improvement soil density in both cases, and (iii) develop design guidelines for densification of silty soils using the above techniques. An analytical procedure was developed and used to simulate soil response during S.C. and D.C. installations, and the results were compared with available case history data. Important construction design parameters and soil properties that affect the effectiveness of these techniques, and construction design choices suitable for sands and non-plastic silty soils were identified. The methodology is expected to advance the use of S.C. and D.C. in silty soils reducing the reliance on expensive field trials as a design tool. The ultimate outcome of this research will be design charts and design guidelines for using composite stone columns and composite dynamic compaction techniques in liquefaction mitigation of saturated silty soils.展开更多
With the aid of soil column test models,the transport rules of fluorine contaminants in unsaturated stratified soils are discussed. Curves of F-concentrations at different times and sites in the unsaturated stratified...With the aid of soil column test models,the transport rules of fluorine contaminants in unsaturated stratified soils are discussed. Curves of F-concentrations at different times and sites in the unsaturated stratified soil were ob-tained under conditions of continuous injection of fluoride contaminants and water. Based on the analysis of the actual observation data,the values between computed results and observed data were compared. It is shown that the chemical properties of fluorine ions are active. The migration process of fluorine ions in soils is complex. Because of the effect of adsorption and desorption,the curve of the fluorine ion breakthrough curve is not symmetric. Its concentration peak value at each measuring point gradually decays. The tail of the breakthrough curve is long and the process of leaching and purifying using water requires considerable time. Along with the release of OHˉ in the process of fluorine absorp-tion,the pH value of the soil solution changed from neutral to alkalinity during the test process. The first part of the breakthrough curve fitted better than the second part. The main reason is that fluorine does not always exist in the form of fluorinions in groundwater. Given the long test time,fluorinions possibly react with other ions in the soil solution to form complex water-soluble fluorine compounds. Only the retardation factor and source-sink term have been considered in our numerical model,which may leads to errors of computed values. But as a whole the migration rules of fluorine ions are basically correct,which indicates that the established numerical model can be used to simulate the transport rules of fluorine contaminants in unsaturated stratified soils.展开更多
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 i...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.展开更多
Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration t...Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration tests on compacted loess with two initial dry densities for different applied vertical stresses were developed using vertical stresscontrollable one-dimensional soil columns.The timehistory curves of vertical deformation,wetting front depth,cumulative infiltration depth,volumetric water content(VWC)and suction were measured,and the soil-water characteristic curves(SWCCs)were determined.The results showed that:(1)the infiltration ability of the soil column weakens with increasing applied vertical stress and initial dry density;(2)vertical deformation increases rapidly at first and then tends to be stable slowly at the consolidation and wetting-induced deformation stage,and is positively correlated with applied vertical stress and is negatively correlated with initial dry density.The stability time of wetting-induced deformation and the corresponding wetting front depth increase with the increase of applied vertical stress,while they decrease obviously when initial dry density increases;(3)the influence of applied vertical stress on soilwater characteristics in soil columns with various initial dry densities is related to the deformation depth of soil column.The VG(Van Genuchten)model is suitable for fitting the SWCCs at different monitoring positions.A normalized SWCC model introducing the applied vertical stress was proposed for each initial dry density using the mathematical relationship between the fitting parameters and the applied vertical stress.展开更多
基金the China Harbor Engineering Company (CHEC) for providing financial support
文摘Both physical and chemical processes affect the fate and transport of herbicides. It is useful to simulate these processes with computer programs to predict solute movement. Simulations were run with HYDRUS- 1 D to identify the sorption and degradation parameters of atrazine through calibration from the breakthrough curves （BTCs）. Data from undisturbed and disturbed soil column experiments were compared and analyzed using the dual-porosity model. The study results show that the values of dispersivity are slightly lower in disturbed columns, suggesting that the more heterogeneous the structure is, the higher the dispersivity. Sorption parameters also show slight variability, which is attributed to the differences in soil properties, experimental conditions and methods, or other ecological factors. For both of the columns, the degradation rates were similar. Potassium bromide was used as a conservative non-reactive tracer to characterize the water movement in columns. Atrazine BTCs exhibited significant tailing and asymmetry, indicating non-equilibrium sorption during solute transport. The dual-porosity model was verified to best fit the BTCs of the column experiments. Greater or lesser concentration of atrazine spreading to the bottom of the columns indicated risk of groundwater contamination. Overall, HYDRUS-1D successfully simulated the atrazine transport in soil columns.
基金Project (No. 50478022) supported by the National Natural Science Foundation of China
文摘The principle and process of parallel seismic (PS) testing for the integrity testing of cemented soil columns are in- troduced in this paper. A three-dimensional (3D) finite element model (FEM) for the pile-soil system is established for impulse responses. Under saturated soil or unsaturated soil condition, several vibrating velocity-time histories at different depths in parallel hole are obtained based on the numerical simulation. It shows that the length of the pile and the one-dimensional (1D) P-wave velocity in the pile can be determined easily from the features of the mentioned velocity-time histories. By examining the slopes of the first arrival time plotted versus depth or the depth where the amplitude of the first arrival significantly decreases, the length of the pile can be determined. The effects of the 3D P-wave propagation through the saturated soil and the defect of the cemented soil column on the velocity-time histories are also investigated.
文摘The adsorption and desorption coefficients of atrazine, methiocarb and simazine on a sandy loam soil were measured in this study with soil column liquid chromatographic (SCLC) technique. The adsorption and desorption data of all the three pesticides followed Freundlich isotherms revealing the existence of hysteresis. In comparing with other methods, SCLC method showed some characteristics such as rapidity, online and accuracy.
基金Bayer AG and Chinese Academy of Agricultural Sciences for kindly supplying the pesticides.
文摘Soil column liquid chromatography (SCLC) was developed to determine soil organic carbon adsorption coefficients (E-oc) for chemicals. The uptake by soil of pesticides from water can be conveniently calculated from the related breakthrough curves (BTC). The nine pesticides chosen for determination in this study are soluble ones, with their water solubility ranging from 62 mg/L to Z mg/L. In comparing with existing methods of K-oc, SCLC possesses rapid, online and accurate characteristics.
文摘Metam sodium （MS; sodium N-methyl dithiocarbamate） has emerged as a promising soil fumigant in the US to replace methyl bromide （MeBr）. Metam potassium （MK; potassium N-methyl dithiocarbamate） and MS break down into the volatile gas methyl isothiocyanate （MITC） to control soil borne pests. Many studies have focused on MS, but MK has not been studied as thoroughly. The objective of this research was to determine the effect of increasing organic matter （OM） treatments and soil texture to minimize the off-gassing of MS and MK. Bench-scale soil column studies were performed to simulate organic matter treatments that may decrease the volatilization loss of MITC. Incorporation depth of OM simulated surface tillage （0-15 cm） practices. Soil was packed in steel columns and MS or MK was applied at a depth of 15 cm and MITC volatilization was measured using gas chromatography/mass spectroscopy. Volatilization of MITC behaved similarly for MS and MK with MITC movement impacted by soil texture. MITC volatilization was lower from a sandy clay loam than a sandy soil. Surface incorporation of OM did not significantly decrease MITC volatilization. These results suggest that soil texture is the dominant factor reducing MITC off-gassing and prolonging the time needed to control soil borne pests.
基金supported by Special Scientific Research Expenditure for Public Charity Industry of Ministry of Water Resources(No.201501008)Institute of Resources and Environment of North China University of Water Resources and Electric Power
文摘The riverbank soil is a natural purifying agent for the polluted river water(Riverbank filtration, RBF). This is of great importance to groundwater safety along the riverbank. This paper examines the migration and transformation rules of ammonia-nitrogen in three typical types of sand soil using the indoor leaching experiment of soil column, and then makes comparison with the indoor experiment results in combination with the numerical simulation method. The experiment process shows that the change in ammonia-nitrogen concentration goes through three stages including "removal-water saturation-saturation". As the contents of clay particles in soil sample increase, the removal of ammonia-nitrogen from soil sample will take more time and gain higher ratio. During the removal period, the removal ratio of Column 1, Column 2 and Column 3 averages 68.8%(1-12 d), 74.6%(1-22 d) and 91.1%(1-26 d). The ammonia-nitrogen removal ratio shows no noticeable change as the depth of soil columns varies. But it is found that the ammonia-nitrogen removal ratio is the least of the whole experiment when the soil columns are at the depth of 15 cm. It can be preliminary inferred that the natural purifying performance of soil along the river for ammonia-nitrogen in river water mainly depends on the proportion of fine particles in soil. HYDRUS-1D model is used to simulate this experiment process, analyze the change of the bottom observation holes by time and depth in three columns(the tenth day), and make comparison with the experiment result. The coefficients of determination for fitting curves of Column 1, Column 2 and Column 3 are 0.953, 0.909, 0.882 and 0.955, 0.740, 0.980 separately. Besides, this paper examines the contribution of absorption, mineralization and nitrification in the simulation process. In the early removal stage, mineralization plays a dominant role and the maximum contribution rate of mineralization is 99%. As time goes by, absorption starts to function and gradually assumes a dominant position. In the middle and late removal stage, nitrification in Column 1 and Column 2 makes more contribution than mineralization. So the experiment result of the ammonia-nitrogen concentration is 0.6% and 2.4% lower than that in effluent and the maximum contribution ratio of nitrification is -4.53% and -5.10% respectively when only the function of absorption is considered. The mineralization in Column 1 and Column 2 in the middle and late removal stage still plays a more important role than nitrification. So the experiment result is 1.4% higher than that in effluent and the maximum contribution ratio of nitrification is -2.51% when only the function of absorption is considered. Therefore, absorption, mineralization and nitrification make different contributions during different part of the stage. This means that the natural purifying performance of soil along the river for ammonia-nitrogen in river water not only depends on the proportion of fine particles in soil, but depends on the mineralization and nitrification environment. This can offer some insights into the protection and recovery of groundwater along the riverbank.
文摘Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter × 28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures： Lyallpur soil series, clay loam （fine-silty, mixed, hyperthermic Ustalfic Haplargid）, and Sultanpur soil series, sandy loam （coarse-silty, mixed, hyperthermic Ustollic Camborthid）. The adsorption isotherms were developed by equilibrating soil with 0.01 tool L^-1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end of the leaching experiment, 0.11 L 10 g L^-1 blue dye solution was also applied to each column to mark the flow paths. The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio （the concentration in solution at equilibrium/concentration applied） was lower than that in the Sultanpur soil columns. The breakthrough of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications for the nutrient management in field soils.
基金the support of a National State Key Project“973”grant(Grant No.:2014CB047000)(sub-project No.2014CB047001)from Ministry of Science and Technology of the People’s Republic of China,a CRF project(Grant No.:PolyU12/CRF/13E)from Research Grants Council(RGC)of Hong Kong Special Administrative Region Government(HKSARG)of China,and two GRF projects(PolyU 152196/14EPolyU 152796/16E)from RGC of HKSARG of ChinaThe authors also acknowledge the financial supports from Research Institute for Sustainable Urban Development of The Hong Kong Polytechnic University,grants(1-ZVCR,1-ZVEH,4-BCAU,4-BCAW,5-ZDAF,G-YN97)from The Hong Kong Polytechnic University.
文摘Geosynthetics and deep cement mixed(DCM)soil columns have been widely used to improve soft soil grounds in many countries and regions.This paper presents an experimental study on a geosynthetic-reinforced sand fill over marine clay with or without DCM columns under different loadings.Two tests were conducted on the sand fill reinforced with fixed-end and free-end geosynthetics over marine clay under three-stage local loading to investigate the effects of the boundary conditions of geosynthetic reinforcement on reducing settlements.It is observed that the fixed-end geosynthetic sheet is more effective in reducing settlements than the free-end condition under identical local loading.Another test was conducted on the fixed-end geosynthetic-reinforced sand fill over the marine clay improved by DCM columns under single-stage uniform loading.The vertical stresses on the marine clay and on the DCM columns,as well as the tensile strains of the geosynthetic sheet in the overlying sand fill,were measured.The results revealed that the stress concentration ratio increases with an increase in consolidation settlements,and the maximum tensile strain of the geosynthetic sheet occurs near the edge rather than at the center of the top surface of the DCM columns.
基金supported by the National Natural Science Foundation of Sichuan Province(22NSFSC0191,22NSFSC3990)。
文摘The combined application of mineral fertilizer and biochar significantly improves the passivation of heavy metal-contaminated soil,surpassing the effects of individual application.This study has reinforced the validation of their passivation competence as soil remediation agents by examining the multifaceted role of potassium-silicon-calcium mineral fertilizer combined with rice husk-based biochar generated at different pyrolysis temperatures.The soil leaching column experiment,conducted based on the adsorption experiments,has facilitated our scrutiny of the passivation impacts of cadmium(Cd)and lead(Pb)when introducing different proportions of mineral fertilizers and biochar into the soil.These results indicate that biochar’s adsorption efficiency for Cd and Pb is significantly improved at escalated pyrolytic temperature conditions in a single solution.The biochar generated at 700℃(C700)renders adsorption effectiveness of approximately 84.24%for Cd and 99.74%for Pb.Biochar conspicuously registers superior adsorption efficiency towards Pb relative to Cd.The mineral fertilizer,which achieves an adsorption efficiency of 97.76%for Cd,is identified as the main adsorbent for Cd,although its competence is slightly lower compared to C700 for Pb adsorption.Within a complex solution,biochar and mineral fertilizer show reduced Cd and Pb adsorption levels compared to single solutions.There is a keen competition for adsorption surfaces witnessed between Cd and Pb,with Pb’s distribution coefficient(Kd)notably outpacing that of Cd.The isothermal adsorption analyses depict that the mineral fertilizer follows the Langmuir model for Cd adsorption,while C700 conveys the Freundlich model for Pb adsorption.The soil leaching column experiment’s results signify that the composite passivation agents significantly outperform the individual passivation agents in efficiency.The combined application of biochar and mineral fertilizer minimizes the cumulative leaching of Cd and Pb,with the optimal soil remedy proportion for heavy metal contamination being 7∶3.In practical application,mindful consideration should be accorded to the deployment ratios of different passivation agents.
基金Federal Highway Administration(FHWA)Under Grant No.DTFH61-98-C-0094
文摘The objective of this study is to develop an analytical methodology to evaluate the effectiveness of vibro stone column (S.C.) and dynamic compaction (D.C.) techniques supplemented with wick drains to densify and mitigate liquefaction in saturated sands and non-plastic silty soils. It includes the following: (i) develop numerical models to simulate and analyze soil densitication during S.C. installation and D.C. process, and (ii) identify parameters controlling post-improvement soil density in both cases, and (iii) develop design guidelines for densification of silty soils using the above techniques. An analytical procedure was developed and used to simulate soil response during S.C. and D.C. installations, and the results were compared with available case history data. Important construction design parameters and soil properties that affect the effectiveness of these techniques, and construction design choices suitable for sands and non-plastic silty soils were identified. The methodology is expected to advance the use of S.C. and D.C. in silty soils reducing the reliance on expensive field trials as a design tool. The ultimate outcome of this research will be design charts and design guidelines for using composite stone columns and composite dynamic compaction techniques in liquefaction mitigation of saturated silty soils.
基金Project 50239010 supported by the National Natural Science Foundation of China
文摘With the aid of soil column test models,the transport rules of fluorine contaminants in unsaturated stratified soils are discussed. Curves of F-concentrations at different times and sites in the unsaturated stratified soil were ob-tained under conditions of continuous injection of fluoride contaminants and water. Based on the analysis of the actual observation data,the values between computed results and observed data were compared. It is shown that the chemical properties of fluorine ions are active. The migration process of fluorine ions in soils is complex. Because of the effect of adsorption and desorption,the curve of the fluorine ion breakthrough curve is not symmetric. Its concentration peak value at each measuring point gradually decays. The tail of the breakthrough curve is long and the process of leaching and purifying using water requires considerable time. Along with the release of OHˉ in the process of fluorine absorp-tion,the pH value of the soil solution changed from neutral to alkalinity during the test process. The first part of the breakthrough curve fitted better than the second part. The main reason is that fluorine does not always exist in the form of fluorinions in groundwater. Given the long test time,fluorinions possibly react with other ions in the soil solution to form complex water-soluble fluorine compounds. Only the retardation factor and source-sink term have been considered in our numerical model,which may leads to errors of computed values. But as a whole the migration rules of fluorine ions are basically correct,which indicates that the established numerical model can be used to simulate the transport rules of fluorine contaminants in unsaturated stratified soils.
基金supported by the United States Sugar Corporation(No.PRO00015244)United States Department of Agriculture(USDA)Hatch Project(No.FLAERC-006097)。
文摘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.
基金funded by the Fundamental Research Funds for the Central UniversitiesCHD(Grant No.300102262503)+2 种基金the Natural Science Basic Research Program of Shaanxi(Grants No.2022JM-167)the National Natural Science Foundation of China(Grant Nos.41790442,41772278,41877242,42072311)the Yan’an Science and Technology Plan Project(Grant No.2022SLSFGG-004)。
文摘Additional stress formed by postconstruction buildings in loess-filling areas affects water infiltration in soil and causes soil deformation.To investigate this effect,under constant water head,vertical infiltration tests on compacted loess with two initial dry densities for different applied vertical stresses were developed using vertical stresscontrollable one-dimensional soil columns.The timehistory curves of vertical deformation,wetting front depth,cumulative infiltration depth,volumetric water content(VWC)and suction were measured,and the soil-water characteristic curves(SWCCs)were determined.The results showed that:(1)the infiltration ability of the soil column weakens with increasing applied vertical stress and initial dry density;(2)vertical deformation increases rapidly at first and then tends to be stable slowly at the consolidation and wetting-induced deformation stage,and is positively correlated with applied vertical stress and is negatively correlated with initial dry density.The stability time of wetting-induced deformation and the corresponding wetting front depth increase with the increase of applied vertical stress,while they decrease obviously when initial dry density increases;(3)the influence of applied vertical stress on soilwater characteristics in soil columns with various initial dry densities is related to the deformation depth of soil column.The VG(Van Genuchten)model is suitable for fitting the SWCCs at different monitoring positions.A normalized SWCC model introducing the applied vertical stress was proposed for each initial dry density using the mathematical relationship between the fitting parameters and the applied vertical stress.
