Electrokinetic(EK)treatment is an effective method in accelerating the consolidation and improving the geotechnical properties of fine-grained soils.This method stabilizes the soil and increases the bearing capacity o...Electrokinetic(EK)treatment is an effective method in accelerating the consolidation and improving the geotechnical properties of fine-grained soils.This method stabilizes the soil and increases the bearing capacity of piles by improving the soil shear strength.Changing the soil p H,due to the occurrence of chemical reactions of electrolysis in the soil,can increase its shear strength.However,the electrodes used in this method corrode due to the change in the soil p H,which in turn reduces the electrical potential.Electrode corrosion and loss of electrical potential can significantly reduce the efficiency of the EK method.In addition,when using the EK method to increase the bearing capacity of piles,changing the p H can cause corrosion and damage to the piles.One of the most important factors influencing the change in the p H of soil is the voltage applied during the EK process.It was reported that increasing the voltage affects the intensity of chemical reactions and electroosmotic flow and thus increases the efficiency of EK.However,very limited research has been conducted on the effect of voltage on the performance of EK method.In the present study,the effects of three voltages on soil p H and corrosion resistance of four types of electrodes including iron(Ir),stainless steel(St),copper(Co),and aluminium(Al)were studied.In addition,the effects of p H variations on the corrosion rate of three types of piles including steel pile(SP),reinforced cement concrete pile(RCCP),and reinforced lime-cement concrete pile(RLCCP)were investigated.It was observed that increasing the voltage from a specific limit had no effect on the intensity of electrolysis reactions and the soil p H adjacent to the electrodes did not change more than a specific limit.Moreover,increasing the voltage to higher than 35 V(i.e.45 V)did not increase the volume of drained water from the soil,but caused more electric current than the allowable current for Ir,St,and Al electrodes,and the corrosion intensity of these electrodes increased significantly.RCCP reduced the soil p H to 2.4 within 7 d of curing due to severe corrosion(13%corrosion rate).The soil p H values adjacent to RCCP and RLCCP within 28 d of curing reduced to 3.7 and 3.8,respectively,but the two piles were not damaged.In general,the results of this research showed that selecting an optimized voltage had a significant effect on the efficiency of EK,and increasing the voltage did not always lead to increase in the efficiency of EK process.展开更多
Plant root exudates contain various organic and inorganic components that include glucose, citric and oxalic acid. These components affect rhizosphere microbial and microfaunal activities, but the mechanisms are not f...Plant root exudates contain various organic and inorganic components that include glucose, citric and oxalic acid. These components affect rhizosphere microbial and microfaunal activities, but the mechanisms are not fully known. Studies concerned from degraded grassland ecosystems with low soil carbon（C） contents are rare, in spite of the global distribution of grasslands in need of restoration. All these have a high potential for carbon sequestration, with a reduced carbon content due to overutilization. An exudate component that rapidly decomposes will increase soil respiration and CO2 emission, while a component that reduces decomposition of native soil carbon can reduce CO2 emission and actually help sequestering carbon in soil. Therefore, to investigate root exudate effects on rhizosphere activity, citric acid, glucose and oxalic acid（0.6 g C/kg dry soil） were added to soils from three biotopes（grassland, fixed dune and mobile dune） located in Naiman, Horqin Sandy Land, Inner Mongolia, China） and subjected to a 24-day incubation experiment together with a control. The soils were also analyzed for general soil properties. The results show that total respiration without exudate addition was highest in grassland soil, intermediate in fixed dune and lowest in mobile dune soil. However, the proportion of native soil carbon mineralized was highest in mobile dune soil, reflecting the low C/N ratio found there. The exudate effects on CO2-C emissions and other variables differed somewhat between biotopes, but total respiration（including that from the added substrates） was significantly increased in all combinations compared with the control, except for oxalic acid addition to mobile dune soil, which reduced CO2-C emissions from native soil carbon. A small but statistically significant increase in pH by the exudate additions in grassland and fixed dune soil was observed, but there was a major decrease from acid additions to mobile dune soil. In contrast, electrical conductivity decreased in grassland and fixed dune soil and increased in mobile dune. Thus, discrete components of root exudates affected soil environmental conditions differently, and responses to root exudates in soils with low carbon contents can differ from those in normal soils. The results indicate a potential for, e.g., acid root exudates to decrease decomposition rate of soil organic matter in low carbon soils, which is of interest for both soil restoration and carbon sequestration.展开更多
基金supported by the Laboratory of Soil and Concrete of Abadgaran Negin Jonoobshargh Company(ANJ Co.)Chem Concrete Pty Ltd.Australia(117/3C-1397)。
文摘Electrokinetic(EK)treatment is an effective method in accelerating the consolidation and improving the geotechnical properties of fine-grained soils.This method stabilizes the soil and increases the bearing capacity of piles by improving the soil shear strength.Changing the soil p H,due to the occurrence of chemical reactions of electrolysis in the soil,can increase its shear strength.However,the electrodes used in this method corrode due to the change in the soil p H,which in turn reduces the electrical potential.Electrode corrosion and loss of electrical potential can significantly reduce the efficiency of the EK method.In addition,when using the EK method to increase the bearing capacity of piles,changing the p H can cause corrosion and damage to the piles.One of the most important factors influencing the change in the p H of soil is the voltage applied during the EK process.It was reported that increasing the voltage affects the intensity of chemical reactions and electroosmotic flow and thus increases the efficiency of EK.However,very limited research has been conducted on the effect of voltage on the performance of EK method.In the present study,the effects of three voltages on soil p H and corrosion resistance of four types of electrodes including iron(Ir),stainless steel(St),copper(Co),and aluminium(Al)were studied.In addition,the effects of p H variations on the corrosion rate of three types of piles including steel pile(SP),reinforced cement concrete pile(RCCP),and reinforced lime-cement concrete pile(RLCCP)were investigated.It was observed that increasing the voltage from a specific limit had no effect on the intensity of electrolysis reactions and the soil p H adjacent to the electrodes did not change more than a specific limit.Moreover,increasing the voltage to higher than 35 V(i.e.45 V)did not increase the volume of drained water from the soil,but caused more electric current than the allowable current for Ir,St,and Al electrodes,and the corrosion intensity of these electrodes increased significantly.RCCP reduced the soil p H to 2.4 within 7 d of curing due to severe corrosion(13%corrosion rate).The soil p H values adjacent to RCCP and RLCCP within 28 d of curing reduced to 3.7 and 3.8,respectively,but the two piles were not damaged.In general,the results of this research showed that selecting an optimized voltage had a significant effect on the efficiency of EK,and increasing the voltage did not always lead to increase in the efficiency of EK process.
基金financially supported by the National Natural Science Foundation of China (41071185, 31170413)the National Basic Research Program of China (2011BAC07B02)Chinese Academy of Sciences has kindly granted Prof. Olof ANDRéN a ‘Professorship for Senior International Scientists’(Y229D91001)
文摘Plant root exudates contain various organic and inorganic components that include glucose, citric and oxalic acid. These components affect rhizosphere microbial and microfaunal activities, but the mechanisms are not fully known. Studies concerned from degraded grassland ecosystems with low soil carbon（C） contents are rare, in spite of the global distribution of grasslands in need of restoration. All these have a high potential for carbon sequestration, with a reduced carbon content due to overutilization. An exudate component that rapidly decomposes will increase soil respiration and CO2 emission, while a component that reduces decomposition of native soil carbon can reduce CO2 emission and actually help sequestering carbon in soil. Therefore, to investigate root exudate effects on rhizosphere activity, citric acid, glucose and oxalic acid（0.6 g C/kg dry soil） were added to soils from three biotopes（grassland, fixed dune and mobile dune） located in Naiman, Horqin Sandy Land, Inner Mongolia, China） and subjected to a 24-day incubation experiment together with a control. The soils were also analyzed for general soil properties. The results show that total respiration without exudate addition was highest in grassland soil, intermediate in fixed dune and lowest in mobile dune soil. However, the proportion of native soil carbon mineralized was highest in mobile dune soil, reflecting the low C/N ratio found there. The exudate effects on CO2-C emissions and other variables differed somewhat between biotopes, but total respiration（including that from the added substrates） was significantly increased in all combinations compared with the control, except for oxalic acid addition to mobile dune soil, which reduced CO2-C emissions from native soil carbon. A small but statistically significant increase in pH by the exudate additions in grassland and fixed dune soil was observed, but there was a major decrease from acid additions to mobile dune soil. In contrast, electrical conductivity decreased in grassland and fixed dune soil and increased in mobile dune. Thus, discrete components of root exudates affected soil environmental conditions differently, and responses to root exudates in soils with low carbon contents can differ from those in normal soils. The results indicate a potential for, e.g., acid root exudates to decrease decomposition rate of soil organic matter in low carbon soils, which is of interest for both soil restoration and carbon sequestration.
