Increase In Hydraulic Conductivity Research Articles

A finite discrete element approach for modeling of desiccation fracturing around underground openings in Opalinus clay

Understanding and predicting potential failure mechanisms during the excavation and open drift stages of geological repository construction are among the crucial aspects of performance evaluation and safety assessment of nuclear waste storage facilities. The development of the Excavation Damage Zone (EDZ) and the generation of shrinkage-induced cracks during operational phases are prominent examples of failure mechanisms that can compromise the integrity of the repository systems. This study presents an integrated framework for investigating shrinkage-induced cracking of Opalinus Clay in niches and tunnels. To achieve this, the hybrid Finite Discrete Element Method (FDEM) is employed. The methodology incorporates a two-way staggered hydro-mechanical coupling scheme, where solid phase analysis relies on 2D FDEM and fluid flow is modeled using the nonlinear Richards’ equation and solved via Finite Volume discretization. To account for the effects of EDZ, characterized by a pronounced increase in hydraulic conductivity, a numerical simulation of tunnel excavation is first carried out. The resulting failure pattern around underground openings is then abstracted through the definition of an altered hydraulic conductivity field. Comparison of the numerical results with field observations demonstrates the framework’s ability to capture a wide range of failure mechanisms inherent in various stages of underground repository construction in Opalinus Clay.

The Effect of Plant Growth-Promoting Bacteria Bacillus subtilis IB-22 on the Hydraulic Conductivity and Abundance of PIP2 Aquaporins in the Roots of an Abscisic Acid-Deficient Barley Mutant.

Little information is available on how rhizosphere bacteria affect abscisic acid (ABA) levels in plants and whether these bacterial effects are associated with improved plant water status. In this study, we tested the hypothesis that the stimulation of plant growth may be associated with the ability of ABA to increase the hydraulic conductivity of roots through the up-regulation of aquaporin. To do this, we studied the effect of bacteria capable of producing ABA on a barley mutant deficient in this hormone. Measurements of hydraulic conductivity of the ABA-deficient barley mutant Az34 showed that its tissues exhibited a reduced ability to conduct water, which correlated with lower ABA content in plants. The inoculation of Bacillus subtilis IB-22 stimulated the growth of both the mutant and its parent variety. Also, under the influence of bacteria, the ABA content in plants increased, and the increase was more significant in the mutant. This effect was accompanied by an increase in hydraulic conductivity in the roots of the ABA-deficient mutant, and immunolocalization using antibodies against PIP2;1 and PIP2;2 aquaporins revealed an increase in their abundance. Thus, the results obtained support the hypothesis about the importance of a sufficiently high ABA content in plants to maintain the abundance of aquaporins, hydraulic conductivity and the growth of barley plants.

Impact of delayed compaction on the geoengineering properties of stabilised pond ash

ABSTRACT The impact of delayed compaction on the geoengineering properties of pond ash (PA) treated with geopolymer, Portland cement, and hydrated lime is presented in this paper. The gradation, compacted dry density (CDD), unconfined compressive strength (UCS), California bearing ratio (CBR), hydraulic conductivity, and compressibility index of PA treated with 3%, 9%, and 15% additive contents were evaluated at 0, 3, 6, 12, 24, 48, and 72 h delay periods. The mineralogical and morphological changes in the stabilised material were assessed using X-ray diffraction and scanning electron microscope analysis. The results show an enhancement in the particle size of PA with delay time due to the development of cementitious products and agglomeration of particles. Delay in compaction causes a reduction in dry density and strength properties, whereas hydraulic conductivity and compressibility index increase with delay time. The formation of cementitious products and agglomeration during delay periods leads to improper compaction and deteriorates the mechanical performance. The formations of both sodium-based geopolymer compounds and calcium-based hydration products contribute to the superior geoengineering properties of geopolymer-stabilised PA compared to cement and lime-stabilised PA, which have Ca-based hydration products alone. The developed mathematical models predict the engineering properties of stabilised PA with higher R-square values (>0.90). Based on this study, it is concluded that the geopolymer is more effective as a stabiliser than lime and cement.

The LTAR Cropland Common Experiment at Upper Mississippi River Basin-St. Paul.

The Soil and Water Management Research Unit of the USDA-Agricultural Research Service is located in St. Paul, MN, and conducts long-term research at the University of Minnesota Research and Outreach Center located at Rosemount, MN. As part of USDA's Long-Term Agroecosystem Research (LTAR) network, the croplands common experiment (CCE) at this location is focused on integration of a kura clover (Trifolium ambiguum M. Bieb.) living mulch (KCLM) system into the prevailing 2-year rotation of corn (Zea mays L.) and soybean (Glycine max L.) that is typical of the midwestern Corn Belt. The LTAR-CCE conducted at Rosemount, MN, aims to compare the long-term environmental and agronomic performance of KCLM while identifying challenges and developing management strategies for this alternative practice. The use of a living mulch for this region is advantageous because, once established, it does not require additional time for fall field operations typically associated with winter cover crops. Results from LTAR-CCE studies at this site show that KCLM results in a substantial increase in soil field-saturated hydraulic conductivity and decreases in leaching of nitrate-nitrogen (NO3 --N). Disadvantages of the KCLM system include potential for increased emissions of nitrous oxide (N2O) and reduced crop yields, particularly during drought. Also, the optimal approach for crop row establishment in the spring remains uncertain. Ongoing LTAR-CCE research with KCLM aims to better understand and quantify both benefits and risks across conditions of interannual weather variability and changing climate to develop guidance for suitable adoption and management of this alternative practice.

Combined effects of geological heterogeneity and discharge events on groundwater and surface water mixing

Stream water (SW) infiltration to the subsurface and subsequent mixing with groundwater (GW) is crucial for controlling water quality in river-corridors. Mixing of solutes from SW and GW triggers biogeochemical reactions, which can attenuate contaminant influx from upstream SW or from GW that eventually enters the river in downstream regions. It is known that geological heterogeneity affects SW-GW exchange fluxes (EF), however, the combined effects of both hydrological and geological aspects (e.g., sand fraction present in the aquifer material) on EF and on SW-GW mixing in strong contrasting bimodal aquifer units remain unclear. Here, we examined this gap by combining geostatistical realizations, fully-integrated numerical flow simulations, and a mixing-cell routine to assess the major controls on EF and to evaluate how mixing develops and is affected by stream discharge events with different magnitudes and durations. Results show that subsurface heterogeneity at the river-reach scale mainly affects EF magnitudes rather than EF patterns. Yet, both EF magnitudes and SW-GW mixing increased with the introduction of subsurface heterogeneity and with the increase of average hydraulic conductivity (K) values and sand fraction in the models. The simulations further indicated a larger potential for mixing under more frequent, short events regardless of the aquifer material, however, mixing values were generally higher for sandier and heterogeneous models. Lastly, for a high K contrast between subsurface units, these effects were more pronounced. This characterization is critical for river restoration strategies and for downstream management of dam-regulated rivers. Our study elucidates the interplay between hydrological and geological controls on the development of SW-GW mixing at intermediate scales and highlights the importance of considering aquifer characteristics in future studies.

Summer cover crop and temporary legume-cereal intercrop effects on soil microbial indicators, soil water and cash crop yields in a semi-arid environment

ContextFew studies have investigated summer cover crops as a replacement for bare fallow in semi-arid temperate regions, and summer cover crop impacts on soil biological function, water balances and subsequent winter crop yields in these regions remain largely unknown. ObjectiveThe 4-year field study aimed to determine the consequences of replacing a summer fallow with a summer growing cover crop on soil function, water balances and subsequent winter cash crop yields in a semi-arid region (486 mm mean annual rainfall) of the Australian southern cropping zone. MethodsA canola (Brassica napus)-wheat (Triticum aestivum L.) rotation with summer fallow was compared to the same rotation with either i) a single species (buckwheat, Fagopyrum esculentum L.) summer cover crop; ii) a four-species mixed brassica + cereal summer cover crop or iii) a cropping sequence with a temporary legume intercrop in the wheat phase of the rotation. Cover crop biomass production, soil water to a depth of 90 cm at cash crop sowing, crop yields and soil functional indices were quantified. ResultsCover crops produced 500–700 kg biomass ha−1 in the 2020 and 2021 seasons and 1000–2400 kg biomass ha−1 in 2022. The four-species mixed cover crop significantly lowered soil water (around 30 mm; P < 0.05) at the time of sowing the cash crop compared to the control and resulted in 15% reduction (P = 0.12) in canola seed yield in 2020, but no significant effect of cover crops of soil water and mineral N at sowing, or cash crop yields, were observed in subsequent seasons. In 2021 the temporary vetch intercrop produced > 1000 kg ha−1 biomass over 9 weeks, and led to a (non-significant) 10% wheat yield reduction. There was no significant effect of cover crop or temporary intercrop treatments on soil functions in the 2020 or 2021 seasons, but activities of several soil enzymes (leucine aminopeptidase, arylsulfatase and B-glucosidase; P < 0.05) and water-soluble carbon (P = 0.059) were significantly higher in the summer cover crop plots compared to control and intercrop plots in March 2022 following termination of the cover crops. These changes coincided with a significant increase in saturated hydraulic conductivity in the four-species cover crop plots in March 2022 compared to control plots. ImplicationsThe study did not provide any compelling evidence for benefits of summer cover crops over fallow in the short term (3–4 years). The relatively low cover crop biomass production over the 4-year study suggests summer cover crops are unlikely to substantially improve soil carbon levels in temperate, semi-arid cropping systems.

Effect of flyash addition to flocculation and freezing and thawing treatment on consolidation of oil sands fluid fine tailings

The total volume of fluid fine tailings (FFT), reached 1,270 Mm3 in 2019. Extensive research is underway by a number of operators to develop dewatering technologies for oil sand tailings reclamation to comply with Directive 085 issued by the Alberta Energy Regulator. A promising technology for the disposal of FFT is to add flocculents and then use thickeners or centrifuges to decrease the water content. Following this treatment, freezing/thawing processes can then be utilized to further dewater the tailings. The effect of flocculation/flyash addition and thickening coupled with freezing/thawing treatments on FFT was investigated by performing large-strain consolidation and shear strength tests on the treated flocculated TTs. It was found that flocculation and thickening treatment increases the hydraulic conductivity of the treated TT which will result in the TT consolidating much faster than the untreated TT. The most important benefit of the flyash addition is the increase in shear strength and hydraulic conductivity of the flyash-treated TTs. The benefit of the freezing/thawing treatment processes coupled with flyash treatment is the increase in the compressibility and hydraulic conductivity at effective stresses lower than 100 kPa and void ratios greater than 1.2, respectively. This will facilitate earlier progressive reclamation required to support hydraulic sand capping.

Leaf hydraulic properties of Antarctic plants: effects of growth temperature and its coordination with photosynthesis.

One of the well-documented effects of regional warming in Antarctica is the impact on flora. Warmer conditions modify several leaf anatomical traits of Antarctic vascular plants, increasing photosynthesis and growth. Given that CO2 and water vapor partially share their diffusion pathways through the leaf, changes in leaf anatomy could also affect the hydraulic traits of Antarctic plants. We evaluated the effects of growth temperature on several anatomical and hydraulic parameters of Antarctic plants and assessed the trait co-variation between these parameters and photosynthetic performance. Warmer conditions promoted an increase in leaf and whole plant hydraulic conductivity, correlating with adjustments in carbon assimilation. These adjustments were consistent with changes in leaf vasculature, where Antarctic species displayed different strategies. At higher temperature, Colobanthus quitensis decreased the number of leaf xylem vessels, but increased their diameter. In contrast, in Deschampsia antarctica the diameter did not change, but the number of vessels increased. Despite this contrasting behavior, some traits such as a small leaf diameter of vessels and a high cell wall rigidity were maintained in both species, suggesting a water-conservation response associated with the ability of Antarctic plants to cope with harsh environments.

АБК-МЕТАБОЛИЗИРУЮЩИЕ БАКТЕРИИ ВЛИЯЮТ НА СОДЕРЖАНИЕ АБК, ИУК И ЦИТОКИНИНОВ И СНИЖАЮТ НЕГАТИВНОЕ ВЛИЯНИЕ НА РОСТ РАСТЕНИЙ САЛАТА ПРИ ЗАГУЩЕННОЙ ПОСАДКЕ

With increasing planting density, ABA accumulates in plants and their growth is inhibited even before resource deficit occurs. In this study, an attempt was made to mitigate this negative manifestation of competition by inoculating lettuce plants with ABA degrading bacteria belonging to Pseudomonas. In laboratory experiments simulating planting density by the number of plants in a pot (one and three plants), similar abilities of bacteria, P. plecoglossicida 2.4-D and P. veronii IB K11-1 to level out the decrease in plant weight in dense planting were found. Both strains reduced the content of the ABA hormone accumulating in competing plants in the soil and in the shoot, increased the IAA content in the roots and in the soil, which sharply dropped in plants with dense planting, and reduced the zeatin content in the roots. The main mechanism of the positive effect of ABA-degrading bacteria on the growth of lettuce plants is discussed as an increase in hydraulic conductivity and improvement of gas exchange as a result of a decrease in ABA in plant shoots, which was supplemented by the direct effect of bacteria on the content of auxins that activate root growth.

Durability of geopolymer cutoff wall backfill incorporating reactive MgO particles under dry-wet cycles

Vertical cutoff wall has been employed for decades to control groundwater flow and subsurface contaminant transport. The barrier performance of cutoff wall material may significantly deteriorate under dry-wet cycles due to precipitation, drought, and groundwater fluctuation. This study adopted active magnesium oxide (MgO) particles to enhance the durability of geopolymer cutoff wall backfill (GCWB) under dry-wet cycles. The influence of particle size and proportion of MgO on the unconfined compressive strength (UCS), hydraulic conductivity, self-healing capacity and durability of GCWB were comprehensively examined. The results indicate that the incorporation of active MgO particles hindered the geopolymerization process of GCWB to a certain extent, leading to an increase in hydraulic conductivity and a decrease in UCS. But the overall performance of GCWB was still favorable. The hydraulic conductivity of samples with MgO gradually increased to more than 1 × 10−8 m/s after at least two dry-wet cycles. In the subsequent cycles, the samples with MgO exhibited a pattern of first gradually declining then ascending in hydraulic conductivity. This is due to hydration and carbonization of the remained MgO in matrix during the dry-wet cycles, which converts into oxygen-rich carbonates, forming well-ramified networks and reducing the proportion of macropores. Thus, the durability of GCWB with MgO is significantly more favorable than that devoid of MgO. In particular, large particle size MgO can exert more persistent self-healing effect, endowing the samples with superior durability under the prolonged dry-wet cycles.

Swelling and hydraulic characteristics of two grade bentonites under varying conditions for low-level radioactive waste repository design

Bentonite is a recommended material for the multiple barriers in the final disposal of low-level radioactive waste (LLW) to prevent groundwater intrusion and nuclear species migration. However, after drying-wetting cycling during the repository construction stage and ion exchange with the concrete barrier in the long-term repository, the bentonite mechanical behaviors, including swelling capacity and hydraulic conductivity, would be further influenced by the groundwater intrusion, resulting in radioactive leakage. To comprehensively examine the factors on the mechanical characteristics of bentonite, this study presented scenarios involving MX-80 and KV-1 bentonites subjected to drying-wetting cycling and accelerated ion migration. The experiments subsequently measured free swelling, swelling pressure, and hydraulic conductivity of bentonites with intrusions of seawater, high pH, and low pH solutions. The results indicated that the solutions caused a reduction in swelling volume and pressure, and an increase in hydraulic conductivity. Specifically, the swelling capability of bentonite with drying-wetting cycling in the seawater decreased significantly by 60%, while hydraulic conductivity increased by more than three times. Therefore, the study suggested minimizing drying-wetting cycling and preventing seawater intrusion, ensuring a long service life of the multiple barriers in the LLW repository.

Effect of leachate contamination in municipal solid waste on clay liner characteristics

Landfill leachate is generated as a consequence of water percolation through the solid waste, oxidation of the waste, and corrosion of the waste. Under-designed landfill sites allow the leachate to easily pass through the soil strata. To identify the effect of contaminants on the engineering properties of the clay liner, a pilot-scale lysimeter was developed. Experiments on two types of soils polluted with leachate were conducted which included silty clay and soil enhanced by chemical stabilization. Lime and silica fume are used as reactive barriers in landfill earthen liners. The leachate generated was monitored periodically and sampled for (pH, Electrical conductivity, Chemical oxygen demand, Chloride, Total dissolved solids, and total suspended solids). Lime (L), silica fume (SF), and lime-silica fume (L-SF) mix have been used for stabilizing soil. Three percentages were used for lime (2%, 4% and 6%) and three percentages were used for silica fume (3%, 5% and 7%) and the optimum percentage of silica fume (5%) was mixed with the proportions of lime. The optimum lime values are 4% from the research and 5% for silica fume. Soil samples were analyzed over a maturation period of 135 days for each run to identify the chemicals and their effect on the soil characteristics. The plasticity index of the stabilized soil continues to decline until it reaches 36% over the 135 days of the maturing period. Furthermore, an increase in silty clay soil hydraulic conductivity was observed from 3.3 × 10−6 cm/sec to 5 × 10−6 cm/sec at 135 days of maturation. Whereas there is a sharp decrease in hydraulic conductivity to achieve a maximum value in the stabilized soil (1.25 ×10−10 cm/sec). Based on laboratory test results, it can be concluded that soil stabilization can improve the geotechnical properties of landfill earthen liners due to pozzolanic reactions.

Investigation of Stability and Underlying Mechanism of Unstable Subgrades Loess Modified by Carbide Slag in Road Construction Projection

The repurposing of carbide slag (CS) coupled with the advancement of eco-friendly engineering methodologies promises a novel approach to addressing the technical challenges inherent in loess refinement. This inquiry delves into the feasibility of employing CS as an economically viable and ecologically sustainable remedy to amplify the engineering attributes of loess within the context of optimal preservation. In this investigation, assorted quantities of CS, spanning from 1% to 6%, were infused into the loess. The efficacy of CS as an additive was ascertained through a comprehensive array of tests administered across varied curing durations (0, 5, 10, 20, and 30 days), concentrating on its influence over the soil’s mechanical attributes. The study conducted various tests such as dual hydrometer, Attberg limit, specific gravity, compaction, unconfined compressive strength (UCS), consolidation, physico-chemical properties (pH, conductivity), and chemical analysis (sodium percentage and sodium adsorption rate). The study demonstrated that the incorporation of CS into loess resulted in an increase in hydraulic conductivity, UCS, and optimum water content while reducing maximum dry density, plasticity, and compressibility. Specifically, the application of 6% CS resulted in a significant 6.7-fold increase in UCS from 226.8 (kPa) to 1508.8 (kPa) over a 30-day curing period. It was also observed that the addition of CS and curing period resulted in a decrease in soil pH from 8.5 to 7.5 and an increase in electrical conductivity (EC) from 250 to 490 μs/cm. When the CS concentration was increased to 6%, the amount of Na+ ions, the total soluble salts, and the percentage of Na in the loess decreased. The phenomenon can be ascribed to the replacement of Ca2+ for Na+, leading to a more slender, diffuse double layer and heightened stability. The application of calcium silicate in loess subgrades enhances their stability and potency, concurrently providing an ecologically sound waste management resolution. Consequently, it emerges as a profoundly viable choice for ameliorating loess within the realm of the construction sector.

The Chemical Compatibility of Sand–Attapulgite Cut-Off Walls for Landfills

Soil–bentonite cut-off walls have been widely used to control landfill pollution but they do not have good chemical compatibility with landfill leachate. Attapulgite can be substituted for bentonite in landfill cut-off walls. However, little is known about the chemical compatibility of attapulgite cut-off walls and leachate. This study experimentally investigated the chemical compatibility of attapulgite cut-off wall specimens with organic and inorganic contaminants and found that a sand–attapulgite cut-off wall has good chemical compatibility with organic contaminants. A CaCl2 solution was used to represent inorganic contaminants, and chemical oxygen demand (COD) was used as an indicator of organic content. The hydraulic conductivity of the cut-off wall initially decreased and then increased to become approximately constant as Ca2+ concentration increased. Changes in COD concentration were divided into a decreasing stage (0–10,000 mg/L) and a constant stage (10,000–40,000 mg/L). The increase or decrease in hydraulic conductivity was by no more than one order of magnitude. The increase in the hydraulic conductivity of the sand–attapulgite cut-off wall is explained in terms of bound water content and pore structure. An increase in Ca2+ concentration decreased the bound water content of the cut-off wall while the CaCl2 solution increased macropore and mesopore volume and decreased small pore volume in the sand–attapulgite cut-off wall. The purpose of this study was to elucidate the chemical compatibility of a sand–attapulgite cut-off wall with organic and inorganic contaminants and to increase the understanding of the interactions between the cut-off wall and the contaminants. The results of this research are informative for improving the application, design, and construction of sand–attapulgite cut-off walls.

Can application of biochar improve the soil water characteristics of silty loam soil?

PurposeThis study investigates if a biochar application in 2014 and its reapplication in 2018 had affected the selected physical and hydrophysical soil properties of silty loam Haplic Luvisol at Dolná Malanta experimental site (Nitra, Slovakia) during the studied period of 2018–2020.Materials and methodsBiochar was produced from cereal husks and paper fiber sludge by pyrolysis at temperature of 550 °C for 30 min and was applied to the soil in doses of 0, 10, and 20 t ha−1. The biochar treatments were combined with three levels of N fertilization (N0, N1, and N2).ResultsBiochar significantly decreased the bulk density up to − 12% and increased the soil porosity up to + 22% even 4–6 years after the biochar application. We also observed an increase in saturated hydraulic conductivity, which was reflected in better precipitation retention and a higher average soil water content by 12–15% depending on the fertilization level. Depending on the level of N fertilization, the interval of plant available water enlarged by 8–51% (10 t ha−1 of biochar), 18–21% (20 t ha−1 of biochar) after single biochar application, and by 18–34% (10 t ha−1 of biochar) and 19–31% (20 t ha−1 of biochar) after reapplication of biochar, which has positive implications regarding providing soil water to plants.ConclusionsThe results indicate that biochar amendments have the potential to substantially improve the soil water characteristics, and therefore, the quality status of silty loam agricultural soils.

Reaction of the carbonate Sibillini Mountains Basal aquifer (Central Italy) to the extensional 2016–2017 seismic sequence

Hydrogeological perturbations in response to earthquakes are widely described worldwide. In carbonate aquifers, a post-seismic discharge increase is often attributed to an increase of bulk permeability due to co-seismic fracturing and the attention on the role of faults to explain the diversion of groundwater is increasing. We focus on the reaction of carbonate hydrogeological basins to extensional seismicity, taking as an example the effects of the Central Italy 2016–2017 seismic sequence, on the Basal aquifer of the Sibillini Mountains area. Geo-structural, seismological and ground deformation data were collected and merged with artificial tracer tests results and with a 4-years discharge and geochemical monitoring campaign. The main NNW-directed groundwater flow was diverted to the west and a discharge deficit was observed at the foot-wall of the activated fault system with a relevant discharge increase, accompanied by geochemical variations, at the fault system hanging-wall. The observed variations are consistent with the combined action of a permeability increase along the activated fault systems, which modified the predominant pre-seismic along-strike regional flow, and with hydraulic conductivity increase due to fracturing, determining a fast aquifers emptying. We show that the prevailing mechanism depends on the aquifer systems position with respect to the activated faults.

Influence of freezing directionality on the permeability of silty clay

During artificial ground freezing, freezing may undergo in directions either parallel or normal to the flow of water, which may result in different permeability for the water to flow. Therefore, it is of significant importance to observe the influence of freezing directionality on the permeability of soils. A set of laboratory permeation tests were performed in this study on specimens subjected to three freeze-thaw modes. Considerable change in hydraulic conductivity subsequent to freeze-thaw event was found even under condition where volume change was not allowed. Vertical freeze-thaw resulted in the lowest level of hydraulic conductivity as compared with the other two cases, irrespective of dry density and moisture content. The permeability of specimen subsequent to radial freezing was approximately 34 times in maximum greater than that subsequent to vertical freezing. The occurrence of vertical cracks was responsible for the dramatical increase in hydraulic conductivity of specimens after radial freeze-thaw. Vertical freeze-thaw, however, resulted in an apparent reduction in hydraulic conductivity because of the local consolidation of soil structure during the growth of horizontal ice lenses. Processes that larger pores became larger but smaller pores became smaller contributed to the increase in hydraulic conductivity of thawed specimens even though the total void ratio was unchanged.

Manure plus Plastic Film Mulch Reduces Soil Salinity and Improves Barley-Maize Growth and Yield in Newly Reclaimed Coastal Land, Eastern China

In newly reclaimed coastal soil, saline conditions and nutrient deficiency are the restraining factors for crop yield. Manure and plastic film mulch are proved to play a vital role in reducing soil salt, increasing soil water, and improving soil nutrients and plant growth. A field experiment was carried out with plastic film mulch, manure, and their combinations in the Tiaozini reclamation area; four treatments were set up as (1) control treatment (CK), (2) plastic film mulch (PM), (3) farmyard manure (FM), and (4) combined application of plastic film mulch and farmyard manure (PM+FM). The main results showed that, compared with CK treatment, the average soil water content under the FM+PM treatment was increased by 5.8% and 3.6%, and the average soil salt content was reduced by 20.2% and 10.0% at 0–20 cm and 20–40 cm soil layers, respectively. This was because of the decrease in soil bulk density and increase in saturated hydraulic conductivity and saturated water content. Meanwhile, soil organic matter, total nitrogen, available nitrogen, and available phosphorus were significantly increased under the PM+FM treatment, except that for AN, which was significantly decreased at the 0–10 cm soil layer owing to plant uptake. Based on the decrease in soil salt, there was an improvement in soil hydraulic properties and soil nutrients, which resulted in summer maize biomass and yield being increased by 106% and 137%, respectively, and barley biomass and yield were increased by 133% and 106%, respectively, under FM+PM treatment. Consequently, combined manure and plastic film mulch application was better at reducing soil salt; increasing soil water content; and improving soil nutrients, plant growth, and yield production in newly reclaimed salt-affected soils.

Swelling Characteristics and Permeability of Bentonite-Based Materials Immersed in Various Solutions

Chemical alterations of bentonite are critical factors for the ultra-long-term stabilization of barriers and backfill in radioactive waste disposal. The chemical alterations may deteriorate the properties of bentonite-based materials. However, experimental studies on the effects of chemical alterations on the swelling characteristics and permeability of bentonite-based materials have not been investigated extensively. In this study, the effects of chemical factors on the swelling properties and permeability of bentonite-based materials were clarified based on one-dimensional swelling-pressure, hydraulic conductivity, X-ray powder diffraction patterns, and element mapping images. From the analytical and experimental results, a small amount of K+, Fe3+, and Mg2+ can significantly deteriorate the swelling characteristic and permeability of bentonite-based materials in geological disposal (i.e., cause a decrease in swelling-pressure and an increase in hydraulic conductivity). Therefore, we conclude that it is necessary to pay close attention to the existence of these cations.

Initial Assessment on Hydraulic Conductivity of Rock Mass and its Size Effect Using Drilling Data

Predicting hydraulic conductivity and characterizing its size effect in jointed rock masses is fundamental to various geoscience and engineering disciplines. A new empirical method, using drilling data, is established to predict the hydraulic conductivity of a rock mass in the scanline direction. The effect of the scanline unit length on the distribution characteristics of hydraulic conductivity for boreholes in jointed rock masses is studied. In addition, the scanline length of boreholes was used to study the size effect of hydraulic conductivity of jointed rock masses, and a new model was proposed to determine the size effect of hydraulic conductivity. A mathematical method for representative volume element (RVE) determination was proposed based on the proposed size effect model of hydraulic conductivity. Some packer tests were conducted to validate the developed method for predicting hydraulic conductivity. The results show that (a) the predicted hydraulic conductivities are close to those determined from the packer tests; (b) the scanline unit lengths influence the distribution characteristics of hydraulic conductivity; (c) a large but fluctuating increase in hydraulic conductivity with increasing scanline length, and the fluctuation decreases with fewer fractures and joints; (d) the mathematical method for predicting RVE and KRVE is effective to make an initial evaluation on jointed rock masses with high fracture frequency.