Soil Columns Research Articles

Investigating Soil Pore Network Connectivity in Varied Vegetation Types Using X-ray Tomography

The ecological environment in southwestern China is fragile. Due to the significant preferential flow in vertical and horizontal directions and poor water conservation ability, vegetation degradation still exists under conditions of abundant rainfall. Therefore, the pore connectivity and infiltration characteristics in shallow soil under typical local vegetation need to be studied. A calculation model for the vertical connectivity of soil macropores was independently constructed, and differences in soil macropore structures and the degree of vertical connectivity in typical vegetation types (natural secondary forest, natural grassland, Yunnan pine plantation, eucalyptus plantation, cypress plantation, mulberry bushes) were investigated by CT scanning technology of undisturbed soil columns. The results showed that the vertical connectivity of large pores in the shallow soil of the region can be quantitatively described by X-ray tomography, and the total surface area and cumulative curvature of macropores in natural grassland soil were two or three times that in artificial vegetation. The concentration area of macropores in the soil of artificial forestland was closer to the surface, and the tendency of macropore preferred path decreased by 76.18% around 30 cm depth in the soil. The vertical connection of soil macropores in artificial forests was significantly lower than that of natural secondary forestlands (33.03%) and natural grasslands (36.75%). The restoration of the plantation improved surface soil pore structure, and the vertical connectivity of soil is nearly 20% less than that of natural vegetation types (natural secondary forestland, natural grassland), which reduced water outflow rate by nearly 44% and electrolyte content by nearly 14% at a depth of 30 cm. This study provided data and research directions for the study of hydrological processes in local forest vegetation and technical support for solving the problems of soil water loss and forestland water conservation in southwestern China.

Insight into the inhibitory mechanism of rhamnolipid biosurfactant on the mobility of sulfonamide antibiotics in saturated soil porous media

The mobility and deposition of sulfonamide antibiotics (SAs) in soil porous media may be impacted by the presence of rhamnolipid (a typical biosurfactant), which is ubiquitous in the natural environment. Herein, the transport characteristics of various SAs, such as sulfamerazine (SMZ), sulfamethazine (SMT), and sulfanilamide (SNM) in soil columns with rhamnolipid, were explored. The mobility of SAs in the soil columns was in the sequence of SNM > SMT > SMZ. The observation was mainly due to the differences in the hydrophobic properties of various antibiotics. Interestingly, rhamnolipid inhibited the mobility of the three SAs over a broad solution pH range (5.0–9.0) primarily because of the interactions between the hydrophobic groups of the deposited rhamnolipid on the soil surfaces and parts of SAs molecules (i.e., rhamnolipid acted as a bridging agent between soil and antibiotic). Furthermore, at a given rhamnolipid concentration, the inhibitory effect of rhamnolipid on SMZ transport was the greatest among the three antibiotics due to SMZ’s greatest hydrophobicity. Additionally, the transport-inhibition influence of rhamnolipid declined as the solution pH values rose. This phenomenon was attributed to the decline of the bridge effects induced by the decreased adsorbed rhamnolipid on soil surfaces. Innovative findings from this study provide helpful information regarding the contribution of biosurfactants on the environmental behaviors of these ubiquitous antibiotic contaminants in soil-water systems.

Effect of Geosynthetics on Swell Reduction During an Extreme Rainfall Event

Expansive (reactive) soils can swell during rainfall causing damage to engineering structures. This paper seeks to investigate the effect of geosynthetic material on the swell reduction of such soils. A series of large-scale long-term soil column experiments were conducted on a very high plasticity reactive soil under simulated rainfall conditions. Non-woven geosynthetics combined with geogrid and woven geosynthetics were used as primary geosynthetic material to provide reinforcement and drainage for the soil mass. The obtained results revealed that these geosynthetics did not improve the California Bearing Ratio values of the soil. However, when placed in the soil mass, the geosynthetic materials greatly reduced the total swell of the soil. Visual observations and the experimental data on water content, suction, and vertical displacements indicated that the geosynthetics provided better drainage of the soil mass. This limited the time of water–soil interaction, thus reducing the total swell of the soil.

LNAPL migration processes based on time-lapse electrical resistivity tomography

Contamination from light non-aqueous phase liquids (LNAPLs) and their derivatives, arising from exploration, production, and transportation, has become a prevalent pollution source. This poses direct threats to human health. However, conventional investigative methods face limitations when applied to studying the extent and migration process of LNAPL contamination, as well as the redistribution of LNAPL during groundwater level fluctuations. Conventional methods lack the ability to rapidly, efficiently, and in real-time acquire information about contaminated areas. Therefore, this study utilizes time-lapse electrical resistivity tomography to investigate the migration mechanism of LNAPL under unsaturated conditions, constant groundwater levels, and groundwater level reductions. A relationship between resistivity and water and oil contents was established and used for inverse calculation of LNAPL content via resistivity inversion. Time-lapse electrical resistivity tomography revealed LNAPL migration in a “concave” shape across three conditions. Groundwater presence notably slowed migration, hindering downward movement and leading to a floating oil band. A robust mathematical model was established to derive the relationship between resistivity and water and oil contents. Finally, LNAPL distribution under unsaturated conditions was inversely obtained from resistivity data, showing highest content at the top leak point, obstructed area, and bottom of soil column. Consequently, time-lapse electrical resistivity tomography demonstrates a notable capacity to characterize the LNAPL migration process. This technique constitutes an effective geophysical method for monitoring and describing the characteristics of LNAPL migration. Its significance lies in enhancing our understanding of remediation for LNAPL-induced groundwater and land contamination.

Impact of Simulated Acid Rain on Soil Base Cations Dissolution between Eucalyptus Pure Plantations and Eucalyptus–Castanopsis fissa Mixed Plantations

The soils of Eucalyptus pure plantations and Eucalyptus–Castanopsis fissa mixed plantations were studied using soil column leaching experiments with acid solutions to mimic the effects of acid rain on the soils. This helped researchers learn more about how soil base ions react to acid deposition and their ability to protect the soil from excessive acidity under pure and mixed-species plantations. The results showed that acid rain leaching increased the leaching loss, desorption, and desorption rate of soil base ions while decreasing the soil pH value, adsorption, and adsorption rate of soil base ions. The soil pH value and the leaching loss ranges of K+, Na+, and Mg2+ were all greater in the pure plantations than in the mixed plantations, while the leaching range of Ca2+ was greater in the mixed plantation than in the pure plantations. In the two types of plantations, the adsorption rates of Ca2+ and Na+ in the mixed plantations were higher than in the pure plantations, while K+ and Mg2+ showed higher adsorption rates in the pure plantations than in the mixed plantations. Therefore, soil pH and base ions were greatly affected by the pH value of acid rain. Compared with the pure plantations, the establishment of Eucalyptus–Castanopsis fissa mixed plantations can slow soil acidification and leaching of K+, Na+, and Mg2+ and contribute to the adsorption of Ca2+ and Na+, which is beneficial for the soil nutrient fixation of Eucalyptus plantations. The mixed plantations were found to increase the exchange reaction between H+ and base ions, thereby improving the acid buffer performance of the soil. This, in turn, helped to mitigate the decline in soil fertility. Therefore, establishment of Eucalyptus–Castanopsis fissa mixed-species plantations can slow down the impact of acid rain on soil acidification in artificial plantation land to a certain extent and play an important role in optimizing the plantation structure of Eucalyptus stands and maintaining their productivity.

Hydraulic circulation technology remediates the contaminated groundwater with petroleum hydrocarbon: Evidence from laboratory and field tests

Removal of contaminants in groundwater in situ conditions is still a challenging problem, with tailing and rebound issues occurring. This study presents a systematic in-situ remediation case by hydraulic circulation in petroleum hydrocarbon-contaminated groundwater in a historically industrial-used site in China. Lab-scale experiments of soil column leaching and in-situ remediation trials were conducted to show the effectiveness of this technology. It has been found that through regulation and optimization of operational measures in five stages, the clean-up goal (1140 μg/L) of the targeted contaminant in groundwater based on the former risk assessment of human health and the intervention value (600 μg/L) in the ‘Dutch Target and Intervention Values (2000)’ were both achieved, and the tailing rebound effect of traditional pump-and-treatment technology was well solved. The combination of groundwater monitoring by ways of pumping pipelines and groundwater monitoring wells could enable workers to timely and effectively grasp the temporal and spatial dynamic variation of pollutants in groundwater in response to the restoration activities, which played an important role in improving the pertinence of pumping-and-injection measures and efficiency of the hydraulic circulation. Discharge standards of wastewater can be reached after being treated with the mass content of added coagulants (Ferrous sulfate) reaching 0.4 g/L and adsorbents (activated carbon) reaching 0.2 g/L. The results demonstrated that it is feasible to conduct in-situ remediation of the contaminated groundwater through hydraulic circulation based on pumping and injection measures and process-monitoring activities, with a competitive operating cost of approximately Rmb 23/m³ and a measured GHG emissions level of 7.12 kg CO2-eq/m³. Overall, the results in this study provide a useful reference case for the realistic remediation of similar sites.

A novel eco-friendly strategy for removing phenanthrene from groundwater: Synergism of nanobubbles and rhamnolipid

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %–19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

Biochar Decreases Fertilizer Leaching and Promotes Miscanthus Growth in Saline-Alkaline Soil.

Biochar has been widely reported to improve soil conditions and affect plant growth. However, its effectiveness is limited by soil type and production technology. Considering the application effect of biochar in saline alkali soil, there is currently a lack of in-depth mechanism explanations in the research. Therefore, we designed an experiment to explore the effect of biochar on plant growth in saline alkali soil and conducted soil column experiments in a greenhouse environment using composite inorganic fertilizer (NPK). The results showed that biochar significantly affected the distribution of soil nutrient content at different depths, with a significant increase in fertility levels in the surface and middle layers and a decrease in fertility levels in deep soils. Compared to using fertilizers alone, the combined use of biochar and fertilizers further expands the enrichment effect and significantly reduces the leaching of fertilizers into deeper layers. At the same time, the application of biochar also improved soil properties, including an increase in electrical conductivity and organic matter content, as well as an increase in soil enzyme activity. On the other hand, the application of biochar also increases the activity of antioxidant enzymes and the content of osmoregulation substances in plants, reducing the environmental stress that plants are subjected to. Therefore, our results indicate that biochar can reduce the leaching of fertilizers into deep soil layers, improve soil properties, and promotes the growth of Miscanthus in saline alkali soils.

Effects of Mycorrhizal and Extraradical Hyphae of Subtropical Native Tree Species on Soil Enzyme Activities and Their Stoichiometric Ratios

We aimed to study the effects of mycorrhizal and extraradical hyphae on soil physical and chemical properties and enzyme activity characteristics in a subtropical plantation and to explore its indicative effect on the effectiveness of soil nutrients. In this study, three native afforestation tree species, Cunninghamia lanceolata, Schima superba, and Liquidambar formosana, with different biological characteristics, root functional traits, and nutrient acquisition strategies in subtropical regions were selected as the research objects. Based on the method of in-growth soil cores, the nylon mesh with different pore sizes was used to limited the root system and hypha into the soil column. The soil physical and chemical properties of five kinds of hydrolase related to the carbon (C), nitrogen (N), and phosphorus (P) cycles were determined in this study. The correlation of different tree species, roots, and mycelia with soil physicochemical properties, enzyme activity, and stoichiometric ratios was analyzed. The results revealed that mycorrhizal treatment significantly affected the soil total carbon (TC) and pH but had no significant effect on hydrolase activity and its stoichiometric ratio. Tree species significantly affected soil physical and chemical properties, soil β-1,4-N-acetylglucosaminidase (NAG), β-1,4-glucosidase (βG), and cellobiohydrolase (CB) activities and soil enzyme stoichiometric ratios. The soil enzyme activity and stoichiometric ratio of the Chinese fir forest had higher values than in monoculture broad-leaved stands of both Schima superba and Liquidambar formosana. There was no significant interaction effect of mycorrhizal treatments and tree species on all soil properties, enzyme activities, and stoichiometric ratios. In addition, the soil enzyme activity and stoichiometric characteristics were mainly affected by the pH. In this study, the soil enzyme activity ratios In(BG + CB):In(AP) and In(NAG + LAP):In(AP) were lower values than the global scale, while the ratios of In(βG + CB):In(NAG + LAP) were higher than the average, indicating that the soil microorganisms in this area were limited by C and P. Moreover, the soil enzyme activity and chemical metrology characteristics were mainly affected by the pH change. In conclusion, differences in litter quality and root functional traits of tree species affected the soil enzyme activity and its stoichiometric characteristics through the shaping of the forest environment by organic matter input, and the influence of pH was the main regulating factor.

Groundwater-level fluctuation effects on petroleum hydrocarbons in vadose zones and their potential risks: Laboratory studies

Despite the role of the vadose zone protecting groundwater from contamination, the non-stationarity in this zone makes it difficult to predict the behavior of petroleum hydrocarbons (PH) therein. In laboratory soil columns with sandy and sandy loam soils, we simulated a vadose zone subjected to repeated groundwater-level fluctuation (GLF) to evaluate the behavior of PH under hydrodynamic conditions. The GLF vertically redistributed the PH, the extent of which was pronounced in the sandy soil with a high initial concentration due to the enhanced transport of the immiscible PH through the larger pores. The frequency of GLF did not show a substantial effect on the extent of PH redistribution but largely affected their attenuation. The greater GLF hindered PH volatilization by maintaining a high degree of water saturation, while the subsequent development of a local anaerobic regime inhibited biodegradation, which was more apparent in the sandy loam. Finally, a specific potential risk index was introduced to quantitatively compare the potential risk of PH contamination in different vadose zones exposed to GLF. Overall, the sandy soil contaminated with the higher total PH (TPH) concentration showed markedly higher potential risk indices (i.e., 18.4–29.0%), while the ones comprised of the sandy loam showed 0.6–4.9%, which increased under the greater number of GLF cycles.

Effect of varying sand percentage in sheath of nature-based capillary barriers composite on water storage capacity and okra growth in arid climate

Agricultural development in many arid countries including Oman is limited due to water scarcity which is currently exacerbated with increasing demand due to rapid population growth, economic development, and mismanagement of water resources. Impact of climate change is expected to adversely impact the water resources. Therefore, finding new efficient, environmentally friendly, and affordable water-saving techniques in agronomy is a necessity for achieving agricultural sustainability. Irrigation water can be saved by creating capillary barriers (CB) to unsaturated moisture flow. In this study, a “nature-inspired capillary barrier design” called hereafter as Smart Capillary Barrier (SCB) (mosaic of fine textured blocks, made of silt loam, and sandy sheath surrounding the blocks) was tested in series of field experiments with soil columns and pots. We investigated the effect of the percentage of sand of the sheath on water storage capacity of the SCB blocks and growth of okra (Abelmoschus esculentus L.) under deficit irrigation. Three proportions of sand to silt loam (sand%:silt loam%) in the sheaths were used in this study, SCB-25 (25:75%), SCB-50 (50:50%) and SCB-75 (75:25%). Our results show that increasing the percentage of sand in the designed and constructed SCB composite reduces evaporative and drainage water losses and therefore increases the water storage capacity of the blocks. Our SCB-75 attains 1.7–1.3 smaller drying rate than that for SCB-25 and SCB-50, respectively. Therefore, this composite had higher water saving capacity than a homogeneous soil (no capillary barrier) and a soil with a standard sand mulch (coarse soil overlies fine soil). The study found that using SCB composite did not consistently have a clear effect on the growth of okra plants at all stages of their development. However, during the development stage, using SCB-75 resulted in significantly higher dry biomass of the plants compared to using a homogeneous soil (the control). Additionally, during the initial stage of fruit yield, using SCB-75 also resulted in significantly higher fruit yield compared to using a homogeneous soil. Application of our SCB composite is a promising approach for saving water in desertic farming.

Influence of Internal Erosion on Rainfall-Induced Instability of Layered Deposited-Soil Slopes

Layered deposited-soil slopes are widely distributed in mountainous terrain. The rainfall-induced instability of layered deposited-soil slopes is not only controlled by the unsaturated infiltration process but also by the seepage-induced internal-erosion process within the deposited soils. In this paper, the main physical processes within two-layer deposited-soil slopes under rainfall infiltration are summarized, and a coupled seepage–erosion finite element model is established to analyze the interactions between the rainfall infiltration process and the internal-erosion process within layered deposited-soil slopes. This finite element model was validated by simulating the coupled seepage–erosion process in a one-dimensional layered soil column. Then, serials of two-dimensional coupled seepage–erosion simulations were conducted to investigate the rainfall-induced seepage–erosion patterns, as well as their impact on the stability evolution of the layered deposited slopes. It was shown that the rainfall-induced seepage–erosion accelerate the water infiltration into the slope and facilitate the generation of subsurface stormflow near the layer interface, which will weaken the soils around the layer interface and accelerate the slope failure process inevitably. Special attention should be paid to the rainfall-induced seepage–erosion effect when evaluating the stability of layered deposited-soil slopes.

Study on the Applicability of Load Calculation Method for Large-Diameter Shield Tunnel in Argillaceous Sandstone Stratum under High Water Pressure

Surrounding rock pressure is an important factor to be considered during designing tunnel structures. In this research, the on-site surrounding rock pressure of a large diameter shield tunnel in argillaceous sandstone stratum was tested, and the evolution process of surrounding rock pressure was analyzed, based on which the variation law of surrounding rock pressure with buried depth and span of the tunnel was discussed. Combined with the numerical simulation method, the applicability of the load calculation method for the large-diameter shield tunnel in the argillaceous sandstone stratum was studied. The results showed that the variation of surrounding rock pressure generally changed from a rapid and substantial increase to a slight decrease and finally tended to be stable. Before reaching stability, the deformation pressure was dominant; then, the loosening pressure became the main pressure, and the surrounding rock pressure almost reached the maximum value in the synchronous grouting stage. Moreover, it was also found that the shield construction had a great influence on the surrounding rock pressure of the 15-ring segments behind the working face. While calculating the surrounding rock pressure, the tunnel section shape, buried depth and surrounding rock conditions should be fully considered. The Full Soil Column Theory, Terzaghi's Theory, Xie's Theory and Bierbauman's Theory were more suitable for tunnels with a buried depth of less than 2.5 hp. When the buried depth of the tunnel exceeded 2.5 hp, the calculation results needed to be enlarged by 2 ∼ 3 times if the Statistical Method or Protodyakonov's Theory was used for calculation. Xie's Theory can be used to calculate the surrounding rock pressure of shallowly buried argillaceous sandstone stratum large-diameter shield tunnel. For a deeply buried argillaceous sandstone stratum large-diameter shield tunnel, it is recommended to use Numerical Simulation Method.

Uranium bioavailability in soil pore water: A long-term investigation in a contaminated soil mesocosm

Uranium in soil can exist in both (IV) and (VI) oxidation states, distributed among different soil fractions (exchangeable, carbonate, oxidizable, reducible, and residual). Following its release from these fractions, uranium enters the soil pore water, becoming bioavailable and potentially posing risks due to its radio and chemical toxicity. Given the significant health and environmental risks associated with uranium, it is crucial to understand its behaviour in contaminated soil pore water and how it changes over time, especially in response to seasonal variations. To address this issue, study was designed to investigate the temporal changes in uranium availability in soil pore water, with a special focus on effect of seasonal variations and biogeochemical reactions that govern the bioavailability of uranium in a contaminated soil mesocosm. This field investigation was carried out for two consecutive years, and revealed that, seasonal variation has a significant effect on the bioavailability of the uranium in the upper soil layers (<30 cm). The biogenic NO3− induced oxidative dissolution of uranium was found to be the predominant reaction causing the dissolution of uranium into soil pore water, followed by ion-exchange in upper layer, whereas at higher depths (30 cm < d < 70 cm) bioavailability is predominantly controlled by ion-exchange reaction. Furthermore, the study shows that at upper layers bioavailability is high during the summer, which is attributed to higher rate of biogenic denitrification and ion exchange reactions. Fast vertical migration of uranium in the soil column is attributed to formation of stable mobile species such as hydroxo‑carbonato ((UO2)xCO3(OH)y−), hydroxo (UO2)x(OH)y and carbonato (UO2CO3) complexes, identified by speciation modelling. For the first time, this study reports the process controlling uranium behaviour in soil pore water and the effect of seasonal variation on it in a contaminated soil. The findings are essential for assessing its potential radiological impact and remediation planning.

Screening the optimal modified biochar for nitrogen retention in black soil.

Reducing the environmental problems caused by nitrogen loss and nitrogen pollution is of great significance. The addition of biochar to soil is a new method for increasing nitrogen interception due to the special structural and physicochemical properties of biochar. The optimal modified biochar was screened out after acid-base modification and batch adsorption test in this paper. And then the effects of different soil and biochar mixing methods on soil physicochemical properties and nitrogen adsorption and retention were explored through soil column leaching test. The results showed that the biochar with a pyrolysis temperature of 700°C had the best adsorption effect on nitrogen after being modified by 0.1mol/L HCI, and the adsorption capacity of nitrate nitrogen reached 121.46 mg/g. The adsorption process of ammonia nitrogen and nitrate nitrogen conformed to the Langmuir model and was mainly homogeneous monolayer. After mixing the selected modified biochar with black soil, the pH increased by 4.77%, the content of ammonia nitrogen increased by 4.89%, and the nitrate content increased by 16.62%. In this study, the adsorption effect of biochar on nitrogen in black soil was discussed, so as to explore the optimal use of biochar in soil, which provided some reference basis for the relevant research.

Exploring the combination of biochar‐amended soil and automated irrigation technology for water regulation and preservation in green infrastructure

AbstractBiochar is a carbon sink material with the potential to improve water retention in various soils. However, for the long‐term maintenance of green infrastructure, there is an additional need to regulate the water contents in the covers to maintain vegetation growth in semiarid conditions. In this study, biochar‐amended soil was combined with subsurface drip irrigation, and the water preservation characteristics of this treatment were investigated through a series of one‐dimensional soil column tests. To ascertain the best treatment method specific to semiarid climatic conditions, the test soil was amended with 0%, 1%, 3%, and 5% biochar. Automatic irrigation devices equipped with soil moisture sensors were used to control the subsurface water content with the aim of enhancing vegetation growth. Each soil column test lasted 150 h, during which the volumetric water contents and soil suction data were recorded. The experimental results reveal that the soil specimen amended with 3% biochar is the most water‐saving regardless of the time cost. Soil with a higher biochar content (e.g., 5%) consumes a more significant amount of water due to the enhancement of the water‐holding capacity. Based on the experimental results, it can be concluded that the appropriate ratio can be determined within 1%–3%, which can reduce not only the amount of irrigated/used water but also the time cost. Such technology can be explored for water content regulation in green infrastructure and the development of barriers for protecting the environment around deep underground waste containment.

Method for Simulating the Anti-Damage Performance of Consolidation Soil Balls at the Roots of Seedlings during Transportation Using Consolidated Soil Columns.

In the process of landscaping or afforestation in challenging terrain, in order to improve the survival rate of transplanted seedlings, it is necessary to transplant seedlings with a mother soil ball attached. During transportation, the soil ball at the root of the seedlings is very susceptible to breakage due to compression, bumps, and collisions. In order to ensure the integrity of the soil ball of the transplanted seedlings and improve the survival rate of seedlings, a method of chemically enhancing the soil surface strength was employed. Specifically, a polymer-based soil consolidating agent was used to solidify the root balls of the seedlings. To examine the abrasion resistance performance of the soil balls formed by consolidating the surface with polymer adhesive during the transportation process, we utilized a polymer-based consolidating agent to prepare test soil columns and developed a method to simulate the damage resistance performance of seedling root balls during transportation using these soil columns. The method primarily encompasses two aspects of testing: compressive strength testing of the consolidated soil columns and resistance to transportation vibration testing. The first method for testing the resistance to transportation vibration of the consolidated soil columns is a combination test that includes three sets of tests: highway truck transportation vibration testing, combined wheel vehicle transportation vibration testing, and impact testing. Although the method is cumbersome, testing is more accurate. The second method for testing the resistance to transportation vibration of the consolidated soil columns involves simultaneously testing multiple consolidated soil columns using a simulated transportation vibration test platform. The testing method is concise and efficient, and the test results are more intuitive. The combined assessment of the resistance to transportation vibration and compressive strength testing of the consolidated soil columns allows for a comprehensive evaluation of the soil columns' resistance to damage during transportation. This study mainly provides a quick and effective method for detecting the damage resistance of consolidated soil columns/balls during transportation, providing technical support for the application of polymer-based consolidation agents in the field of seedling transplantation.

Transformation and Leaching Simulation of 6:2 and 8:2 diPAP and Related Metabolites in Unsaturated Soil Column Studies with MACRO

PFAS (perfluoroalkyl substances) are widespread in the environment and are found in almost every medium. Besides persistent PFAS, their transforming precursors gained attention since they may be a reservoir for persistent PFAS in soil. Only little information is available about the behavior of these precursors and the simultaneous leaching of their transformation products. However, this information is urgently needed to improve estimates of contamination levels. For this purpose, two precursors and their non-degradable metabolites were simulated using the MACRO model, with parameter values optimized using the evolutionary algorithm caRamel. A constant first-order transformation rate did not adequately represent the leaching of transformation products, but a variable transformation rate that decreased at the date of an equilibrium soil moisture provided a good representation of the precursor transformation and leaching of transformation products. The results are new evidence that variable environmental parameters such as soil moisture may affect the transformation rate of precursors. The simulation study is a step towards describing the behavior of PFAS precursors through physically-based models.

Spatial distribution and risk assessment of polycyclic aromatic hydrocarbons in soils from contaminated sites in Eastern China.

A total of 16 polycyclic aromatic hydrocarbons (PAHs) were measured in 28 soil column samples from two contaminated industrial sites in Eastern China. The total concentration of 16 PAHs (∑PAHs) in the surface soil (0-20cm) was measured up to 52,600ng/g (dry weight basis) with a remarkable spatial difference in the studied contaminated sites. The concentrations of the ∑PAHs in soils decreased with the increase in soil depth (0-10m). The surface and subsurface soil presented a tenfold higher concentration than the soil with depth greater than 4m. Additionally, the vertical migration tendency of the PAHs was found to be correlated significantly with their hydrophobicity (R2 = 0.79, P < 0.01). Naphthalene (with lowest octanol-water partition coefficient among the studied PAHs) showed the greatest average soil depth at which its peak concentration occurred. Furthermore, risk quotient analysis by using benzo[a]pyrene as reference compound showed that 71.4% of the samples exhibited high ecological risk for soil. Moreover, the total carcinogenic risk of the PAHs in the surface soil samples was assessed at 5.61 × 10-5-1.28 × 10-4 and 4.41 × 10-6-9.43 × 10-5 for male and female workers, respectively, in which 67.9%-71.4% of the samples showed potential risk. Generally, these results suggest a further consideration of ecological and health risks associated with PAHs in contaminated sites in Eastern China.

A semi-implicit material point method for coupled thermo-hydro-mechanical simulation of saturated porous media in large deformation

The coupled thermo-hydro-mechanical (THM) response of liquid-infiltrated porous media underpins the safe operation and maintenance of key engineering infrastructure. Challenges remain in modeling and understanding the complicated multiphysics processes of porous media subjected to THM loads and undergoing large deformation. In this study, we develop a stabilized material point method (MPM) for modeling the THM responses of large deformation problems in biphasic solid–fluid mixtures. A novel and efficient staggered solution scheme is proposed to solve the governing equations of the coupled system formulated in terms of four primary variables: solid displacement (u), liquid velocity (v), pore pressure (p), and temperature (T). The scheme solves the energy balance equation first and employs the resulting temperature to further advance the calculation of the momentum and mass balance equations using a semi-implicit fractional step method to facilitate equal-order interpolations. Both the incompressible and weakly compressible fluid are considered in the presented fractional step formulations. We also develop the axisymmetric form of the coupled MPM to increase the applicability and efficiency of the method in THM problems. The validity, stability, and robustness of the proposed method are demonstrated through three benchmark problems, including the heating of a saturated half-space, the non-isothermal consolidation of a soil column, and a three-dimensional axisymmetric problem pertaining to the thermoelastic response around a point heat source. The predictive capability of the proposed method for large deformation problems is further showcased by the simulation of the progressive failure process of a thermal-sensitive slope.