Decrease In Hydraulic Conductivity Research Articles

Effect of rising damp in unstabilized rammed earth (URE) walls

The effect of rising damp on the Thermal-hydro-mechanical (THM) behavior of Unstabilized Rammed Earth (URE) structures has been rarely studied in literature. To consider this effect, we use a validated theoretical framework implemented in a finite element code for the THM behavior of URE materials. The effect of rising damp is then investigated and compared with the same wall not influenced by the rising damp. The simulation results show that time plays a positive role on the THM properties of an URE wall because the evaporation process reduces the humidity, decreases the water content, increases the thermal insulation and improves the mechanical strength of the wall. In contrast, the rising damp plays an opposite role since it has a cooling effect on the wall temperature. The wall dries more quickly and the water also flows fast to the bottom side of the wall. Without rising damp, the horizontal bearing capacity increases 47% when the time passes from 7 days to 1825 days after construction, while this increase is only 10% with the rising damp. The decrease of thermal insulation resistance and hydraulic conductivity becomes less in the wall with the rising damp after five years.

Global meta-analysis suggests that no-tillage favourably changes soil structure and porosity

Role of soil to meet global food security, sustainable intensification and food nutritional quality has got renewed attention with a larger focus on soil physical condition. No-tillage (NT) practice can essentially contribute to develop a sustainable, low carbon and resource efficient agriculture, and encourage the use of crop residues for added soil benefits. Soil aggregation and pore size distribution, two most important soil physical factors controlling the mass and energy transport processes within the soil and between soil and environment, were evaluated under the NT through a global meta-analysis of 5065 pairs of data points from 419 peer-reviewed studies. Compared to conventional tillage (CT), NT increased mean weight diameter of aggregates, water stable aggregates, and macroaggregates by averages (0–30 cm) of 25, 10 and 22%, respectively, although predominantly in 0–10 and/or 10–20 cm layers, with an accompanying reduction in microaggregates. A small but significant 3% decrease in total porosity, a large reduction (20–32%) in macroporosity and a moderate increase (4–7%) in microporosity were realized under NT up to 20 cm soil depth. Bulk density remained stable, although a very large decrease (70% change over CT) in saturated hydraulic conductivity was recorded in 10–20 and >30 cm soil layers. Years of adoption of NT had an additive effect on mean weight diameter and macroaggregates, and the total and macroporosity. Increase in latitudes favoured soil aggregation and micropore volume under NT, while clay content was unfavourable to macro- and water stable aggregate contents. Improvement in structure and water retention properties relate to long-term sustainable development of soils by following no-till practice, which has far-reaching implications beyond the boundaries of agronomy.

Numerical Model about the Influence of Cyclic Load on the Hydraulic Conductivity of Soft Clay

The hydraulic conductivity k is one of the most important engineering properties of soft clay, and it plays an important role during the whole life cycle of underwater tunnel. Therefore, it is necessary to systematically study the response of k to dynamic load. In this study, a series of seepage tests were conducted on remolded Hangzhou soft clay using dynamic triaxial seepage apparatus after cyclic loading. The results show that the hydraulic conductivitys of all samples decrease after cyclic loading, and the maximum drop of the hydraulic conductivity can reach 29.1%. Also, the hydraulic conductivity of soil samples is significantly affected by cyclic stress ratio (CSR). With the increase of CSR, the decrease range of hydraulic conductivity under cyclic loading is between 22.3% and 24.3%. The dynamic load reconstructed the microstructure of clay and made the number of large pores getting decreased and the small pores increased. This resulted in a decrease in the smaller hydraulic conductivity (k) of the specimens. Futhermore, based on the NMR scanning on the microstructure of soil samples under cyclic loading and the microscopic pore channel theory, a prediction model for the k of soft clay is proposed. The validity of the model is verified based on test data. It is believed that the proposed model could provide some theoretical support for the design and long-term performance prediction in practical engineering issues.

The role of biochar particle size and hydrophobicity in improving soil hydraulic properties

AbstractThe physical properties of biochar have been shown to dramatically influence its performance as a soil amendment. This study assessed the role of biochar particle size and hydrophobicity in controlling soil water movement and retention. Softwood pellet biochar in five particle size ranges (>2 mm, 2–0.5 mm, 0.5–0.25 mm, 0.25–0.063 mm and <0.063 mm) was used for the experiment. These particle sizes were tested on two soil types (sandy loam and loamy sand) at four different application rates (1, 2, 4 and 8%) in the laboratory. Soil water suction at wet range and dry range were measured using the Hyprop and WP4‐T, respectively. From this, the moisture content at field capacity (fc), permanent wilting point (pwp) and plant available water (awc), were determined. Saturated hydraulic conductivity (Ksat) was measured using the KSAT device and biochar hydrophobicity was determined using the ethanol drop test method. Our results showed that biochar hydrophobicity increased with decreasing biochar particle size, leading to a reduction in its water retention capacity. The highest fc (0.087 cm−3 cm−3) and awc (0.064 cm−3 cm−3) were observed for soils amended with >2 mm biochar. The soil hydraulic conductivity increased with decreasing biochar particle sizes, with the exception of <0.063 mm biochar, which showed a significant (p ≤ 0.05) decrease in soil hydraulic conductivity compared to the larger particle sizes. The results clearly showed that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affected mainly hydraulic conductivity; both interpores and intrapores controlled soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended.Highlights Biochar increases soil water retention and reduces hydraulic conductivity. Hydrophobicity of biochar increased with decreasing particle size. Coarse biochar particles increased soil water retention due to hydrophilic surfaces and increased intraporosity. Fine biochar particles decreased hydraulic conductivity due to reduced macropores.

Leakage through a hole in a geomembrane beneath a fine-grained tailings

Leakage through a 10 mm diameter circular hole in a geomembrane beneath fine-grained tailings is examined for a range of pore pressures and effective stresses. Leakage was measured in an experiment with coupled physical and hydraulic conditions to simulate the effective stresses and flow conditions near the hole. The leakage rate was as little as 0.16 L/day with 200 kPa pore pressure (10–30 kPa effective stresses) and increased only to 0.46 L/day with 800 kPa pore pressure (200 kPa effective stress). Seepage analysis of the experiment and local measurements of permeability from small samples extracted after the experiment indicate that the tailings hydraulic conductivity controlling flow was 3–6 × 10−9 m/s. Only a subtle decrease in hydraulic conductivity (less than 2 times) near the hole was found. No evidence of seepage-induced migration of fines within the tailings was found. Calculations with the parameters deduced from the experiment show that leakage from a tailings storage facilities containing fine-grained tailings can be limited to 1–2 L/ha/day with a geomembrane liner, even when containing up to five 10 mm diameter holes per hectare, as opposed to an unlined facility with 3 to 4 orders of magnitude more leakage.

Effects of pH and EC on the strength and permeability of plastic concrete cutoff walls.

At present, plastic concrete is widely used in anti-seepage engineering, and its strength and hydraulic conductivity are important indexes of plastic concrete cutoff walls. The pondus hydrogenii (pH) and electrical conductivity (EC) have an important effect on the strength and hydraulic conductivity of plastic concrete cutoff walls. However, it is not clear why the pH and EC are related to the strength and permeability of these walls. For this reason, plastic concrete composed of sand, cement, water, and bentonite was taken as the research object to study the influence of different mix ratios and curing ages on the unconfined compressive strength and permeability of plastic concrete. The pH and EC of the corresponding mix ratio and curing age were measured. The effects of the pH and EC on the strength and permeability of plastic concrete were studied, and the internal reason was explored from the product type and hydration reaction degree of plastic concrete. Furthermore, the quantitative relationship between pH and EC and the strength and hydraulic conductivity of plastic concrete was established. With increasing cement content, the strength, pH, and EC of plastic concrete increase continuously, while the hydraulic conductivity decreases. With increasing curing age, the strength increases, the hydraulic conductivity decreases, and both the pH and EC show a trend of first increasing and then decreasing. The pH value and electrical conductivity can reflect the product type and hydration reaction degree of plastic concrete, further affecting its strength and hydraulic conductivity. Under different dosage and curing age conditions, the pH showed three stages, namely, 11.7-12.27, 12.27-2.5, and 12.5-12.75, and there is a good power functional relationship among the EC and strength and hydraulic conductivity at each stage.

A microstructural investigation on hydraulic conductivity of soft clay

The hydraulic conductivity is a key parameter in geotechnical engineering. It is closely associated to soil microstructure. In practice, consolidation stress, dry density, and natural structure of soil can affect pore diameter and distribution of soil. Thus, to investigate soil hydraulic conductivity, their effects on microstructure and the corresponding hydraulic conductivity were analyzed. The undisturbed soil and the remolded soil with different dry densities were studied by the oedometer tests, hydraulic conductivity tests, and field emission scanning electron microscope (FESEM) tests. The results indicate that the natural structure inside the undisturbed soil is the intrinsic reason that affects hydraulic conductivity. The increase of consolidation stress mainly reduces the number and size of interaggregate pores in terms of provoking aggregation of soil particles. The increase in dry density will fill the interaggregate pores and weaken their connectivity. The area percentage of macropores can be used to reflect the change of soil microstructure. The consolidation stress is the main factor dominating the area percentage of macropores under a high-stress level. A stable intrinsic structure will be developed to inhibit the soil deformation when dry density is 1.4 g/cm3 or above, which helps to restrain the reduction of area percentage and slow down the decrease of hydraulic conductivity. Finally, a brief statistical regression analysis indicates that the area percentage of pores whose diameter larger than 0.4 μm is significantly related to the hydraulic conductivity, which are responsible for seepage in soft clay.

Experimental investigation on seepage erosion of the soil–rock interface

Internal erosion under seepage flow affects the hydraulic and mechanical behavior of the soil, which is one of the most important factors of geological disasters. Due to that the soil–rock interface can be the potential preferential seepage channels commonly, the characteristics of erosion are more significant and hazardous at the soil–rock interface. In this study, a series of laboratory experiments are performed to investigate the failure mechanism and evolution of interfacial seepage erosion. The influences of two essential influence factors (i.e., the confining pressure and the roughness of the interface) are investigated by comparing the seepage velocity, hydraulic conductivity, failure hydraulic gradient, and failure hydraulic shear stress in experiments. Furthermore, the failure pattern of interfacial seepage erosion is particular investigated by the CT scanning. The interfacial seepage erosion tests indicate that the interfacial seepage erosion shows a three-phase progressive failure as the hydraulic gradient increases and the hydraulic conductivity decrease with the progress of suffusion in the initiation phase. The increase of confining pressure leads to the increase of failure hydraulic gradient. The results of CT scanning show that the roughness of the soil–rock interface significantly affects the size and shape of resulting zone of erosion.

ИЗМЕНЕНИЕ ВКЛАДА АКВАПОРИНОВ В ГИДРАВЛИЧЕСКУЮ ПРОВОДИМОСТЬ РАСТЕНИЙ НА ФОНЕ ФОРМИРОВАНИЯ АПОПЛАСТНЫХ БАРЬЕРОВ ПОД ВЛИЯНИЕМ ЗАСОЛЕНИЯ

The study of plant adaptation mechanisms during the salt stress is required to provide an increase in plant productivity under such conditions. Along with a decrease in the availability of water for plants, the NaCL-induced inhibition of plant growth is associated with the toxic effect of sodium ions. The formation of apoplastic barriers due to the deposition of suberin and lignin restricts passive ion diffusion. However, the formation of such barriers reduces the capacity of the apoplastic pathway for water movement. In these conditions the role of transmembrane water transport is increased. This process is provided by aquaporin water channels. Thus the purpose of this work was to determine the contribution of aquaporins to hydraulic conductivity of peas plants under salinity-induced apoplastic barrier formation. An only slight decrease in plants transpiration caused by mercury chloride in the absence of salinization was in accordance with the ideas the apoplast is the dominant pathway when the Casparian bands is not formed yet. Salt stress in our experiments accelerated the development of the Casparian bands formation which could be visualized as an appearance of suberin strips in root endodermis which in turn was accompanied by a decrease in hydraulic conductivity. The decrease in hydraulic conductivity in 2 times during the mercury chloride treatment under salinity confirmed that contribution of aquaporins to the total hydraulic conductivity was increased under conditions when Casparian bands have had formed.

Влияние засоления на устьичную и гидравлическую проводимость, а также на уровень аквапоринов в клетках листьев растений ячменя, различающихся по солеустойчивости

We studied participation of aquaporins in the regulation of leaf hydraulic conductivity and relationship of hydraulic conductivity with accumulation of ABA and stomatal closure during salt stress. Using the method of immunohistochemical localization we showed that salinity led to greater decline in the level of aquaporins in the region of the vascular leaf bundles of the more salt-tolerant Prairia cultivar, accompanied by a noticeable decrease in hydraulic conductivity of the leaf. In the less salt-tolerant plants of the Mikhailovsky cultivar, significant changes in the level of aquaporins under the influence of salt stress were not found. The degree of decrease in the hydraulic conductivity of the leaf in plants of two cultivars under the influence of salt stress correlated with a decrease in transpiration. Immunohistochemical localization of abscisic acid (ABA) in leaf cells showed that during salt stress this hormone accumulated in leaf mesophyll cells and stomata. The uptake of exogenous hormone from the nutrient solution and its entry into the leaf through the vascular bundles was accompanied by an increase in staining for aquaporins and the hydraulic conductivity of the leaves, which is characteristic of the ABA action. Differences in the localization of exogenous and endogenous hormones were obviously the cause of the opposite directions of changes in hydraulic conductivity: its increase under the influence of an exogenous ABA and a decrease - under the influence of salt stress. ABA concentration assessment in xylem showed the absence of its increase during salt stress, which explains the absence changes of staining for this hormone in the region of the leaf vascular bundles and indicates that accumulation of ABA in a short-term salt stress is not the result of its delivery from the roots, but the result of its synthesis in the shoot itself.

Effect of Strain-Dependent Hydraulic Conductivity of Coal Rock on Groundwater Inrush in Mining

Hydraulic conductivity is an important parameter for predicting groundwater inrush in coal mining worksites. Hydraulic conductivity varies with deformation and failure of rocks induced by mining. Understanding the evolution pattern of hydraulic conductivity during mining is important for accurately predicting groundwater inrush. In this study, variations of hydraulic conductivity of rock samples during rock deformation and failure were measured using the triaxial servo rock mechanic test in a laboratory. The exponential formula of hydraulic conductivity-volume strain was proposed based on the experimental data. The finite-difference numerical model FLAC3D was modified by replacing constant hydraulic conductivity with the strain-dependent hydraulic conductivity. The coupled water flow and rock deformation and failure were simulated using the modified model. The results indicate that in the early time, the rocks undergo elastic compression with increasing rock strain, resulting in a decrease in hydraulic conductivity; then, the microcracks and fissures appear in the rock after it yields results in a sudden jump in hydraulic conductivity; in the later time, the hydraulic conductivity decreases gradually again owing to the microcracks and fissures that were compacted. The conductivity exponentially decreases with the volumetric strain during the periods of both elastic compression and postyielding. The simulated stress-strain curves using the modified model agree with the triaxial tests. The modified model was applied to the groundwater inrush of a coal mining worksite in China. The simulated water inflow agrees well with the observed data. The original model significantly underestimates the water inflow owing to it to neglect the variations of the hydraulic conductivity induced by mining.

The Singular Molecular Conformation of Humic Acids in Solution Influences Their Ability to Enhance Root Hydraulic Conductivity and Plant Growth.

Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed.

Drought resistance in oat involves ABA-mediated modulation of transpiration and root hydraulic conductivity

Drought is one of the most important constraints to crop productivity worldwide. Control of plant responses to drought is very complex. The mechanisms and their intensity may differ between species and/or genotypes ultimately conditioning tolerance or susceptibility. We explore here the strategy set up by two oat cultivars to cope with drought based on root morphological, anatomical, physiological and molecular studies. A dramatic and rapid abscisic acid increase in the susceptible genotype resulted in a tight and rapid reduction of stomatal conductance. Despite of this, leaf water potential decreased concomitantly due to a decrease in root hydraulic conductivity. By contrast, the resistant genotype, showed a mild and slow increase in abscisic acid that allowed maintaining transpiration longer. This response was linked to an increase in root hydraulic conductance through an increase in total root length and in the length of the thinnest roots as well as a rise in root conductivity. This was also coupled with anatomical changes leading to a reduction of metabolic cost. These changes allowed the resistant genotype to maintain higher water potential reducing drought symptoms and promoting growth under water deficit conditions.

Changes in soil physical and hydraulic properties following the conversion of forest to cropland in the black soil region of Northeast China

Black soils (Mollisols) are inherently productive and fertile but are deteriorating due to long-term intensive cultivation. Understanding the changes in soil physical and hydraulic properties in topsoils and deep soils after converting forest to cropland would reveal the mechanism related to the black soil degradation. Herein, we investigated the variations in the soil water-stable aggregates, soil water content, bulk density, field capacity, total porosity, saturated hydraulic conductivity, and parameters of soil water retention curve at the 0–100 cm depth in four sampling fields. These fields included a forest as control and three croplands that were converted from forest 41, 50 and 65 years ago in the black soil region of Northeast China. We showed that converting forest to cropland decreased >2 mm aggregates and aggregate stability especially at 0–15 and 70–100 cm depths, with a greater decrease in cropland after relatively longer time of cultivation. Conversion of forest to cropland significantly decreased the soil water content at the 0–15 cm depth but increased it at the 15–100 cm depth, and the increase in the 50–100 cm soil layer was strengthened with cultivation time. The decreases in field capacity, total porosity and saturated hydraulic conductivity and increase in bulk density at the 0–50 cm depth following the conversion of forest to cropland were higher after 41 and 50 years of cultivation than those after 65 years of cultivation. However, changes in these metrics at the 50–100 cm depth increased with cultivation time. The parameters (i.e., θr, θs, α and n) of the soil water retention curve were not affected by the cultivation time after converting forest to cropland. These results highlighted that long-term cultivation after the conversion of forest to cropland resulted in the changes in soil physical and hydraulic properties in the 0–100 cm soil profiles, and thus, the response of deep soils should not be ignored in this black soil region.

Relation between flow through and volumetric changes in natural expansive soils

Geology and climate govern the evolution and behavior of natural expansive soils in the semi-arid Canadian Prairies. The Regina clay deposit has a flat topography, a homogenous composition, and contains hair-line fissures. This research focuses on understanding the relation between flow through and volumetric changes in the natural expansive soil. Based on analysis of test data, it is concluded that flow occurs through macro-pores or fissures (5 × 10−8 m/s) during structural volume change and through micro-pores or matrix (10−9 m/s) during normal and residual volume changes. The hydraulic conductivity decreases by several orders of magnitude and becomes asymptotic vapor flow (2 × 10−14 m/s) during residual volume change. A complete assessment of soil behavior requires water retention, swell-shrink, and hydraulic conductivity curves. The proposed straight-line representation of the functions' components is useful for predicting field response of expansive soils.

Contrasting functional strategies following severe drought in two Mediterranean oaks with different leaf habit: Quercus faginea and Quercus ilex subsp. rotundifolia.

Nowadays, evergreen sclerophyllous and winter-deciduous malacophyllous oaks with different paleogeographical origins coexist under Mediterranean-type climates, such as the mixed forests of the evergreen Quercus ilex subsp. rotundifolia Lam. and the winter-deciduous Quercus faginea Lam. Both Mediterranean oaks constitute two examples of contrasting leaf habit, so it could be expected that they would have different functional strategies to cope with summer drought. In this study, we analysed photosynthetic, photochemical and hydraulic traits of different organs for Q. faginea and Q. ilex subsp. rotundifolia under well-watered conditions and subjected to very severe drought. The coordinated response between photosynthetic and hydraulic traits explained the higher photosynthetic capacity of Q. faginea under well-watered conditions, which compensated its shorter leaf life span at the expense of higher water consumption. The progressive imposition of water stress evidenced that both types of Mediterranean oaks displayed different functional strategies to cope with water limitations. Specifically, the decrease in mesophyll conductance associated with edaphic drought seems to be the main factor explaining the differences found in the dynamics of net CO2 assimilation throughout the drought period. The sharp decline in photosynthetic traits of Q. faginea was coupled with a strong decrease in shoot hydraulic conductance in response to drought. This fact probably avoided extensive xylem embolism in the stems (i.e., 'vulnerability segmentation'), which enabled new leaf development after drought period in Q. faginea. By contrast, leaves of Q. ilex subsp. rotundifolia showed effective photoprotective mechanisms and high resistance to drought-induced cavitation, which would be related with the longer leaf life span of the evergreen Mediterranean oaks. The co-occurrence of both types of Mediterranean oaks could be related to edaphic conditions that ensure the maintenance of soil water potential above critical values for Q. faginea, which can be severely affected by soil degradation and climate change.

Can Heating Induce Borehole Closure?

The current study shows that heating a cased borehole in low-permeability shale rock can induce plastic deformation, leading to the closure of the casing annulus and decreasing annulus connectivity. The thermally induced borehole closure is interesting for the field operation of plug and abandonment (P&A), as it potentially saves operation cost and time by avoiding cutting casing and cementing. Lab experiments and numerical simulations are implemented to investigate the thermally induced borehole closure. Pierre shale and a field shale are tested. The lab experiments are performed by heating the borehole wall in a 10-cm-OD hollow cylinder specimen. Here, a novel experimental setup is applied, allowing for measuring temperature and pore pressure at different radii inside the specimen. Both the experimental data and the post-test CT images of the rock samples indicate the rock failure by borehole heating, and under certain conditions, heating results in an annulus closure. The decrease of hydraulic conductivity through the casing annulus is observed, but this decrease is not enough to form the hydraulic-sealed annulus barrier, based on the results obtained so far. Lab-scale finite-element simulations aim to match the lab results to obtain poro-elastoplastic parameters. Then the field-scale simulations assess the formation of shale barriers by heating in field scenarios. Overall, (i) the lab experiments show that heating a borehole can increase the pore pressure in shale and hence induce rock failure; (ii) the numerical simulations match the experimental results reasonably well and indicate that the heating-induced borehole closure can sufficiently seal the casing annulus in the field-scale simulation.

Splash erosion affected by initial soil moisture and surface conditions under simulated rainfall

Soil erosion by water is one of the most severe soil degradation processes. Splash erosion is the initial stage of soil erosion by water, resulting from the destructive force of rain drops acting on soil surface aggregates. Apart from rainfall properties, constant soil physical properties (texture and soil organic matter) are crucial in understanding the splash erosion. However, there is lack of information about the effect of variable soil properties such as soil initial water content and surface condition (seal formation) on splash erosion. The objective of the present study was to determine how initial water content and surface condition affected soil splash erosion under simulated rainfall. The changes in soil surface condition were characterized by hydraulic variability (saturated hydraulic conductivity) due to surface seal formation. Slit loam and loamy sand soil textures were used in the experiment. The soil samples were collected from the top layer; air dried, and filled into modified Morgan splash cups for splash erosion measurements. Rainfall was created in the laboratory using two types of rainfall simulators covering intensity range from 28 to 54 mm h−1 and from 35 to 81 mm h−1. The soil samples were exposed to three consecutive rainfall simulations with different time intervals between simulations and different initial water content and surface conditions (air-dried, wet-sealed, and dry-crusted). Wet-sealed soil samples had up to 70% lower splash erosion rate compared to air-dried samples, due to surface ponding followed by seal formation. A significant decrease in soil saturated hydraulic conductivity indicated the formation of surface seal for silt loam soils. A non-significant decrease in saturated hydraulic conductivity for loamy sand soil was attributed to earlier formation of stable seals. Two different rainfall simulators produced different amount of splash erosion rates; however, the splash erosion development for increasing rainfall intensity was almost equal considering same initial surface condition. These results provide insight into dynamic changes of individual soil parameters affected by rainfall, and could find wider application for more complex soil erosion prediction models.

Size-dependent biochar breaking under compaction: Implications on clogging and pathogen removal in biofilters

Breaking of biochar during compaction of amended soil in roadside biofilters or landfill cover can affect infiltration and pollutant removal capacity. It is unknown how the initial biochar size affects the biochar breaking, clogging potential, and contaminant removal capacity of the biochar-amended soil. We compacted a mixture of coarse sand and biochar with sizes smaller than, similar to, or larger than the sand in columns and applied stormwater contaminated with E. coli. Packing columns with biochar pre-coated with a dye and analyzing the dye concentration in the broken biochar particles eluted from the columns, we proved that biochar predominantly breaks under compaction by disintegration or splitting, not by abrasion. Increases in biochar size decrease the likelihood of biochar breaking. We attribute this result to the effective dissipation of compaction energy through a greater number of contact points between a large biochar particle and the adjacent particles. Most of the broken biochar particles are deposited in the pore spaces of the background geomedia, resulting in an exponential decrease in hydraulic conductivity of amended sand with an increase in suspended sediment loading. The clogging rate was higher in the columns with small biochar. The columns with small biochar also exhibited high E. coli removal capacity, partly because of an increase in bacterial straining at reduced pore size after compaction. These results are useful in selecting appropriate biochar size for its application in soils and roadside biofilters for stormwater treatment.

Influence of the features of the unsaturated zone on the air injection method in a slope

The drainage of groundwater is essential to slope stabilisation in both potential and existing landslides. Air injection is a new method for slope drainage that aims to control rapid rises in the groundwater level by creating an artificial unsaturated zone with low permeability. The interception ratio, reflecting the effectiveness of the air injection method in intercepting groundwater, is defined in this paper and the effects of the length and hydraulic conductivity of the unsaturated zone on the interception ratio are studied through theoretical analysis, physical tests and numerical simulations. The results show that, in the initial stage, the interception ratio increases quickly with an increase in the length of the unsaturated zone. The interception ratio then gradually stabilises, with the stable value depending on the decrease in hydraulic conductivity of the unsaturated zone. The findings reported in this paper are important for improving the design of the air injection method.