Silt Layers Research Articles

Leakage detection applied to the Da-Hedong Reservoir dam (China) based on the flow-field fitting method

Detecting leakage in concrete gravity dams presents a formidable challenge. The Flow-Field Fitting (FFF) method is used to identify leaks in China’s Da-Hedong reservoir dam. We propose vertical- and horizontal-gradient approaches based on the transmitted signal electrical field. A plastic frame is developed to allow the probe to measure horizontal gradients. We determine the exact location of leaks at the reservoir’s bottom and upstream face, respectively, assuming that current leakages are located in hydraulic leakage zones. Numerical experiments and water pressure tests reveal that the conductive silt layer beneath the reservoir can lower the response of the potential values at the leakage inlet, and the effect of the silt layer should be considered and not ignored when interpreting measured data. In addition, with regards to the principle of superposition, the contribution associated with metal pipes in the dam body can be roughly determined by subtracting it from the original potential field data, thereby aiding in locating leaks around the metal pipes. Additionally, the FFF measurements from the reservoir’s bottom also confirm the position of existing faults in the substratum at the reservoir site. Lastly, the results of the FFF method are tested against supporting evidence including ground penetrating radar and water pressure tests. In conclusion, these independent data confirm the effectiveness of the FFF method for leakage localization in the concrete gravity dam.

Wave-induced residual response and liquefaction of a nonhomogeneous layered seabed

Numerical studies were conducted on the wave-induced residual liquefaction of a silt–coarse sand layered seabed. Fully dynamic soil equations and residual seabed response equations were incorporated into the development of a numerical model. The numerical results were compared with theoretical solutions and experimental data from previous studies. Relatively good agreement was found in this comparison, validating the reliability of the proposed numerical model. The present model was applied to systematically investigate the wave-induced residual response with a silt–coarse sand layered seabed. The effects of coverage thickness, permeability, Young’s modulus in the upper silt layer on the residual response of the seabed were carefully examined. Numerical simulations indicate that the potential liquefaction is prone to occur with low permeability of the upper silt layer and shallower water depth, and the effect of coverage thickness of the silt layer on pore pressure and liquefaction potential is determined by shear stress ratio (χ) and effective normalized spreading parameter (Se) which represent the “generation power” and “dissipation potential” for residual pore pressure. The performance of the pore pressure and liquefaction in the layered seabed is the result of a trade-off between two non-dimensional parameters.

Assessing soil vulnerability in Petobo post-liquefaction zone, Palu, Central Sulawesi: A microzonation study utilizing microtremor measurements

On September 28, 2018, a 7.5 Richter magnitude earthquake struck the Palu City neighborhood of Petobo. The tectonic activity along the Palu-Koro fault generated this earthquake, which resulted in soil liquefaction. The purpose of this study is to use microtremor measurements at 33 distinct places to investigate the properties of the soil layer after liquefaction. The obtained data was then evaluated utilizing Horizontal to Vertical Spectral Ratio (HVSR) methodologies such as Ground Shear Strength (GSS), amplification factor, and vulnerability index to determine the soil layer's properties and susceptibility. The dominant frequency ranges from 0.19 to 4.75 Hz, while the dominant period ranges from 0.21 to 5.17 seconds, according to the measurement results. According to these measurements, the silt layer varies between 5 and 30 m. GSS values in the 10-4 to 10-2 range indicate that soil cracking, subsidence, liquefaction, landslides, and compaction are likely. The soil vulnerability and amplification index values range from 2.36 to 4.37, respectively. These values show the potential level of danger, which might be low, medium, high, or extremely high. Peak ground acceleration varied from 299.52 to 301.52 gals, suggesting high to extremely high danger levels. The microzonation map created for this study is considered to be a useful resource for training disaster mitigation approaches and facilitating infrastructure development planning in the region.

Wolffia globosa (Araceae s. l. / Lemnaceae s. str.), a new aquatic alien species in the flora of Ukraine

In Europe, Wolffia globosa was first recorded in 2002 in the RF, and not in Bulgaria, as it was previously believed. Over the past 20 years, the species has expanded its secondary range. As of 2023, it is known from seven European countries. In Ukraine, W. globosa was first found in 2023 in two localities in Zhytomyr Region (Zhytomyr Polissia). The plant communities with W. globosa in Ukraine belong to the association Lemno-Spirodeletum polyrhizae of the alliance Lemnion minoris of the class Lemnetea. In the reported localities W. globosa occurs in eutrophic stagnant waterbodies with depths of 0.2–0.5 m and weakly flowing waterbodies with depths of 1.2–1.5 m; silty bottom is covered by a silt layer 5–20 cm thick, lighting is full. It is suggested that due to the observed climate warming, further migrations of W. globosa to other regions of Ukraine are possible.

Comprehensive distribution characteristics and factors affecting the migration of chromium in a typical chromium slag-contaminated site with a long history in China.

The contamination of abandoned chromium slag-contaminated sites poses serious threats to human health and the environment. Therefore, improving the understanding of their distribution characteristics and health risks by multiple information is necessary. This study explored the distribution, accumulation characteristic, and the role in the migration process of chromium. The results showed that the contents of total Cr and Cr (VI) ranged from 12.00 to 7400.00mg/kg, and 0.25 to 2160.00mg/kg, respectively. The average contents of both total Cr and Cr (VI) reached the highest value at the depth of 7-9m, where the silt layer retaining total Cr and Cr (VI) was. The spatial distribution analysis revealed that the total contamination area percentages of total Cr and Cr (VI) reached 7.87% and 90.02% in the mixed fill layer, and reduced to 1.21% and 34.53% in the silty layer, and the same heavily polluted areas were located in the open chromiumresidue storage. Soil pH and moisture content were the major factors controlling the migration of total Cr and Cr(VI) in soils. Results of probabilistic health risk assessment revealed that carcinogenic risk was negligible for adults and children, and the sensitive analysis implied that the content of Cr(VI) was the predominant contributor to carcinogenic risk. The combination of chemical reduction and microbial remediation could be the feasible remediation strategy for soil Cr(VI) pollution. Overall, this study provides scientific information into the chromium post-remediation and pollution management for various similar chromium-contaminated sites.

Seismic Failure Mechanisms of Concrete Pile Groups in Layered Soft Soil Profiles

So far, little attention has been paid to the investigation on the seismic failure mechanisms of flexible concrete pile groups embedded in the layered soft soil profiles considering the material non-linearities of soil and concrete piles. The purpose of this study is to investigate seismic failure mechanism models of flexible concrete piles with varied groups in silt layered loose sand profiles under horizontal strong ground motions. Three-dimensional finite element models of the pile–soil interaction systems, which include nonlinearities of soil and concrete piles as well as coupling interactions between the piles and soil, were created for Models I, II, and III of the soil domains, encompassing 1x1, 2x2, and 3x3 flexible pile groups with diameters of 0.80 m and 1.0 m. Model I consists of a homogenous sand layer and a bedrock, Models II and III are composed of a five-layered domain with homogeneous sand and silt soil layers of different thicknesses. The linear elastic perfectly plastic constitutive model with a Mohr–Coulomb failure criterion is considered to represent the behavior of the soil layers, and the Concrete Damage Plasticity (CDP) model is used for the nonlinear behavior of the concrete piles. The interactions between the soil and the pile surfaces are modeled by defining tangential and normal contact behaviors. The models were analyzed for the scaled acceleration records of the 1999 Düzce and Kocaeli earthquakes, considering peak ground accelerations of 0.25 g, 0.50 g, and 0.75 g. The numerical results indicated that failure mechanisms of flexible concrete groups occur near the silt layers, and the silt layers have led to a significant increase in the spread area of the damaged zone and the number of damaged elements.

Investigating stone column effectiveness for sabkha soil improvement: field tests and numerical model

AbstractThis study explores the application of stone columns to improve the bearing capacity of sabkha soil for the construction of a Lattice Communication Tower foundation in the Eastern Province of Saudi Arabia. Geotechnical investigation report, an on-site footing loading test to evaluate the foundation's bearing capacity and settlement behavior following stone column installation, and post-cone penetration tests (CPT) to assess soil densification are all part of the study data. The uppermost 4 m of the soil profile comprise a medium to dense layer of sand with silt, followed by a 12-m layer of weak sabkha soil (SPT, N less than 4). Below the sabkha layer, the strata exhibit varying densities, ranging from medium to dense and very dense layers, extending to the maximum depth of investigation. The comparison of Pre- and Post-CPT data revealed significant improvements in the sand and silt layer above the sabkha layer, as well as moderate improvements in the upper portion of the sabkha layer. However, the majority of the sabkha soils and underlying soil layers did not show significant improvement. Plaxis 3D numerical models were employed to provide insights into the performance of the composite area encompassing stone columns and the surrounding soil. Comparing field tests and numerical models showed that neglecting stone column installation effects in numerical models led to overestimating settlements. However, when examining the field data and numerical results with a raised coefficient of lateral earth pressure when of $${K}_{^\circ }=2$$ K ∘ = 2 , a distinct alignment between settlement values consistent with those derived from field testing. The findings highlight the importance of including site-specific conditions and installation effects in numerical modeling to accurately predict the behavior of stone columns in sabkha soils.

Diverse sedimentary organic matter within the river-aquifer interface drives arsenic mobility along the Meghna River Corridor in Bangladesh

In alluvial aquifers with near-neutral pH and high dissolved arsenic (As) concentrations, the presence and character of sedimentary organic matter (SOM) regulates As mobility by serving as an energetically variable source of electrons for redox reactions or forming As–Fe-OM complexes. Near tidally and seasonally fluctuating rivers, the hyporheic zone (HZ), which embodies the mixing zone between oxic river water and anoxic shallow groundwater, may precipitate (or dissolve) iron (Fe)-oxides which sequester (or mobilize) As. To understand what is driving the mobilization of As within a shallow aquifer and riverbank sands adjacent to the tidally fluctuating Meghna River, we characterized the chemical reactivity of SOM from the sands, and a silt and clay layer, underlying the HZ and aquifer, respectively. Dissolved As (50–500 μg/L) and Fe (1–40 mg/L) concentrations increase with depth within the shallow aquifer. Similar vertical As and Fe concentration gradients were observed within the riverbank sands where concentrations of the products of reductive dissolution of Fe-oxides increase with proximity to the silt layer. Compared to all other sediments, the SOM in the clay aquitard contains older, more recalcitrant, terrestrially-derived material with high proportions of aromatic carboxylate functional groups. The shallow silt layer contains fresher SOM with higher proportions of amides and more labile polysaccharide moieties. The SOM in both the riverbank and aquifer is terrestrially-derived and humic-like. The labile SOM from the silt layer drives the microbially mediated reductive dissolution of As-bearing Fe-oxides in the HZ. In contrast, the carboxylate-rich SOM from the clay aquitard maintains dissolved As concentrations at the base of the aquifer by complexing with soluble As and Fe. This highlights that SOM-rich fine (silt or clay) layers in the Bengal basin drive As and Fe mobility, however, the specific processes mobilizing As and Fe depend on the lability of the SOM.

Sheet Pile Failure Caused by Scouring and Sand Mining at Padang River Bank

Ground movement occurred on the banks of the river in Padang which has been protected by steel sheetpile which borders the Factory property. Indications of ground movement are detected through visual observations. It was also reported that the day before the incident there had been continuous rain until the next day. Based on the results of the technical drilling, it appears that the soil density becomes lower after 10m depth. There is a layer of sandy silt with a soft to medium consistency at a depth of about 18m to 26m. With soil conditions that are dominated by sandy soil, the risk of scouring due to river flow is one of the things that needs to be considered. Landslides occur gradually because changes in river flow patterns gradually changed due to internal and external factors. Internal factors are caused by the flow and behavior of the river itself, while external factors are the activity of mining of sand material around the riverbanks. Along with the swift river flow, especially during flood water conditions, the layers of soil material move and are washed away by the flow of water so that there is a gap between the sheetpile and the original soil. These conditions cause the passive resistance of the sheet pile to gradually decrease and to experience deformation due to the pushing of the soil material that has experienced a movement. Important findings in the investigation is that the very soft clay layer underneath the sandy layers was not detected prior to the investigation.

Geoelectric Method for Groundwater Identification in Pangkalarang

Meeting the need for clean water is one of the supporting conditions for creating good public health. Clean water can be obtained from several sources, including ground water, river water, dug well water, and so on. Likewise, people in the Pangkalarang area are experiencing a clean water crisis. They have difficulty getting clean water and can only rely on dug well water which is brownish red in color, similar to tea water and has a slight metallic smell. And of course this water is not suitable for consumption and can only be used for watering plants, washing clothes and bathing. The condition of clean water may be influenced by the condition of the Pangkalarang area which has swamps and is a coastal area, so it is possible that water pollution from dug wells may occur. The Pangkalarang area has a source of clean water in the form of groundwater whose existence needs to be known to make it easier for the community to determine the position of the drilled well. Therefore, researchers consider it necessary to investigate the existence of groundwater which is a source of clean water using Geoelectric methods in the Pangkalarang area. This Geoelectric method uses a Schlumberger electrode configuration to obtain information on the position and depth of the aquifer. This electrode configuration has the advantage of good vertical resolution so that it can represent groundwater depth conditions in detail along with information on the types of silt or rock layers in or around the aquifer. The results of observations and research data processing using IPI2Win software show that there is a very Geoelectric point position that can be used as a reference for determining the drilled well point, namely at a depth of 87 m it is estimated that water can be found, but it is still very likely to be mixed with sea water. Therefore, researchers recommend that groundwater drilling be carried out to a depth of 87 - 164 meters.

Prediction models for effective PVD-enhanced in-situ flushing remediation of multi-layered soils

The re-utilization of original industrial sites poses a significant challenge in the remediation of contaminated soils, driven by the transformation of urban industrial spaces. In this study, a prediction model is proposed to address this challenge by focusing on the in-situ flushing remediation of multi-layered soils enhanced with PVDs. The analytical model is versatile for various scenarios where the boundaries have different diffusion capacities by introducing imperfect diffusion boundaries. It incorporates the effects of the sandy silt layer and the decay characteristics of initial contaminant concentrations with depth on remediation efficiency of multi-layered contaminated soils. To validate the model, the solutions derived from the matrix analysis were compared with experimental data and numerical simulation results from COMSOL Multiphysics. Parametric analysis reveals that the model effectively captures different boundary conditions ranging from fully non-diffusive to completely diffusive by utilizing the imperfect diffusion capacity coefficient within the range of 0 to 50. Furthermore, the remediation of the upper and lower silty clay layers of the sandy silt layer was different but both decreased in efficiency as the thickness of the sandy silt layer increased. Notably, the concentration of the contaminant exhibits more pronounced variations with increasing radial dispersivity compared to vertical dispersivity.

The Luna structure, India: A probable impact crater formed by an iron bolide

The Luna structure of India has been rumored to be an impact crater for more than a decade without any convincing evidence. This structure (1.5–1.8 km) is prominently visible in the low-lying Banni Plains of the tectonically active Kutch Basin as a circular morphological feature with a less-prominent rim. Luna area is strewn with melt-like rocks having high specific gravity and displaying wide range of magnetic properties. It contains minerals like wüstite, kirschsteinite, ulvöspinel, hercynite, and fayalite. The whole rock analysis denotes PGE enrichment, with notably higher average concentrations of Ru (19.02 ppb), Rh (5.68 ppb), Pd (8.64 ppb), Os (6.03 ppb), Ir (10.63 ppb) and Pt (18.31 ppb). The target is not exposed at Luna, owing to the overlying thick sequence of Quaternary sediments. The mineralogical and geochemical signatures points to an impact into a target, which is rich in clay with elevated calcium and silica (sand/silt) content. Geochemical data suggests an iron or stony-iron meteorite as the potential projectile at Luna. The silt layer containing plant remnants, underlying the strewn layer, yielded a radiocarbon age of 6905 years, making Luna the biggest crater to result from an iron bolide within the last 10,000 years.

Identification of Geothermal System in Cisolok, West Java based on the Correlation of Gravity Method, ADMT (Active Directory Magnetotelluric), and Drill Log Data

Indonesia has 40% geothermal potential of the world’s geothermal potential. One proof of its potential is in Cisolok, West Java. The method used in this study is the gravity method from 2013 GGMPlus satellite with First Horizontal Derivative (FHD) analysis which is correlated with ADMT and drill log data. Based on overlaid between Land Surface Temperature (LST) map and residual anomaly map, Cisolok has a temperature of around 23.8 – 26.5 °C. These correlations describe the normal fault structure in the south that controls the Cisolok geothermal system. The results of the 3D inversion modeling show alternating layers of tuff, tuff breccia and silt as a cap rock with a density contrast of 0 – 0.2 gr/cc at a depth of 0 – 325 m, thick limestone layers with a density contrast of -0.1 – (-0.05) gr/cc at a depth of 325 – 700 m, and a layer of granodiorite rock as an intrusion body with a density contrast of -0.2 – (-0.15) gr/cc at a depth of 700 – 900 m. Based on the results obtained, it can be proven that the gravity method and the ADMT method have a fairly good correlation in geothermal exploration activities.

How do Different Types of River Maintenance Works Affect the Ichthyofauna of Small European Watercourses?

Abstract Watercourses serve the needs of agriculture in certain sections and are subject to strong anthropopressure. When agriculture prevails in the catchment, it often has abundant vegetation, macrophytes in particular, and the bottom is covered by a substantial layer of silt. In order to ensure patency of flow and access to water, small watercourses are very often subject to river maintenance works. The aim of the study was to assess the impact of 3 types of works on the diversity of fish species and density of fish in the 1 and 2 year after the works at 21 sites located on 8 rivers in the European Central Plains Ecoregion. As a result of the works, especially in the 1 year after the works, significant changes were found in hydrochemical and hydrological parameters, especially with the increase in velocity and mean depth in watercourses. Additionally, habitat change contributed to differences in the composition of the ichthyofaunal. After 1 year, the diversity of fish species and fish population density increased or remained unchanged after dredging and removal of plants from the river channel, but they decreased after the removal of macrophytes from river banks. After year 2, a decrease in the diversity of fish species and density was observed, associated with re-infestation and siltation of the watercourses. Particularly in the case of dredging and removal of macrophytes from the river bank, maintenance works should not be done too frequently, because some species of natural value disappear.

The deep soil water dynamics and its environmental controls after long-term revegetation

The increase in the extreme drought trend, reduction in soil erosion, and acceleration of deep soil desiccation are renewing interests in soil water dynamics and its environmental controls after long-term (>30 years) grass and shrub revegetation on the Chinese Loess Plateau (CLP). However, inconsistent findings have been reported on soil water dynamics in these typical land uses due to the multi-dependent environmental controls. The objectives of this study are to identify the spatial variability of soil water dynamics and its controls in a small watershed. For this purpose, spatiotemporal soil water storage in 1 m interval to a depth of 5 m was decomposed into a temporal mean (i.e., time-stable pattern) and temporal anomaly (Atn), which varies over time and is related to soil water dynamics. Atn was then decomposed into a space-invariant temporal anomaly (i.e., spatial mean of Atn) and a space-variant temporal anomaly (Rtn), which reflects the spatial variability of soil water dynamics. The Rtn was further decomposed using the empirical orthogonal function (EOF) to identify its major controls. Results showed that soil water dynamics (gain and loss) decreased from grassland to abandoned cropland followed by shrubland after long-term revegetation. The hot spots in deep soil water dynamics (2–5 m) were identified in layered soils with an overlying sand layer and underlying silt layer, and grassland with the coexistence of tree-shrub-grass and high deep soil organic carbon (SOC) content. 50–70% of the total variations of Rtn were explained by the first two spatial patterns (EOFs). Silt and SOC content controlled EOF1 of Rtn at 0–2 and 2–5 m, respectively. Plant canopy and soil profile properties (e.g., layered soils with an overlying sand layer and underlying silt layer) controlled EOF2 of Rtn at 0–1 and 2–5 m, respectively. The EOF analysis suggests that silt and SOC dominated soil water storage capacity, plant canopy regulated water flux, and variations of hydraulic properties in soil profiles may jointly drive spatial variability of soil water dynamics.

Identification of modern meteoric water, glacial meteoric water, and fossil seawater in a deep borehole at the coastal area of Horonobe, north Japan, using groundwater dating and paleoclimatic proxy methods

Groundwater flow in deep areas of coastal regions has attracted significant attention for geological radioactive waste disposal or geological CO2 storage. To investigate groundwater flow in coastal areas, groundwater dating methods with the potential to assess slow groundwater flow were used at depths of up to 1200 m at Hamasato, Horonobe, northern Japan. Multiple groundwater dating methods were applied using pore water in drilling core and pumping groundwater. This study shows that modern meteoric water, glacial meteoric water, and fossil seawater are distributed in sand and silt layers at 300–360 and 90–300 m in depth and in silt and mud layers below 800 m in depth, respectively. Modern meteoric water infiltrated after and glacial meteoric water infiltrated during the latest glacial period were identified using δD and δ18O values, estimated recharge temperature from noble gas concentrations, and 14C concentrations. The estimated recharge temperatures of modern and glacial meteoric waters were 8.1 ± 2.0 and 2.1 ± 2.0 °C, respectively, whereas the δD and δ18O values were −68 ± 3‰ and −10.3 ± 0.2‰, −81 ± 2‰ and −11.4 ± 0.3‰, respectively. The 14C age of modern meteoric water was 10–16 ka. However, the 14C age of glacial meteoric water could not be estimated because it was highly diluted by 14C-free CO2 from methanogenesis and marine carbonate dissolution. Fossil seawater was identified using δD, δ18O, 36Cl, and 4He. δD and δ18O values underwent water-rock interaction and approached inland fossil seawater with increasing depth. 36Cl/Cl values did not reach secular equilibrium in situ in the Yuchi Formation due to its relatively short geological age and consolidation-induced porosity changes. However, the Yuchi Formation seawater is considered extremely old because its 36Cl/Cl ratio is higher than that of modern seawater as a result of 36Cl production, which also explains the observed 36Cl/Cl increases with depth toward the secular equilibrium ratio (36Cl/Clse). 4He concentrations were in the order of 10−6 ccSTP/gw, corresponding to an in situ accumulation age of 1–2 Ma, neglecting the external flux. The contribution of external flux could be negligible for the short geological age and rapid sedimentation rates. 4He ages were equivalent to the geological age of the Yuchi Formation. Core investigations can interpolate groundwater investigations because cores, particularly those from low-hydraulic conductivity layers, can be collected continuously. In addition, stable and radioactive isotopes and noble gases can help identify modern meteoric water, glacial meteoric water, and fossil seawater, assisting in understanding the groundwater flow velocity.

Field test on the mechanism of composite bucket foundation penetrating sandy silt overlying clay

Composite bucket foundation has been gradually applied in China, involving six tilting supports to connect an upper pillar with a lower suction bucket with even honeycomb components separated by bulkheads. However, there are limited field measurements for such new type of offshore wind turbine foundation structure currently. In this study, field test campaign is launched to investigate the evolution of critical parameters for composite bucket foundation during the penetration process in soils. Results indicate that the coefficient of lateral pressure on the exterior skirt increases dramatically when traversing a shallow sandy silt layer, and the maximum value is approximately 2.81 times the passive soil pressure coefficient; the presence of negative pressure within the bucket causes a coefficient of lateral pressure on the interior skirt within the range between active and passive pressure coefficients. Nonetheless, as the penetration depth increases, the muddy-silty clay layer inside the bucket prevents further generation of seepage channels. By comparing the volume of seawater discharged from the bucket with its penetration volume into the mud surface, it is found that the bucket is under an over-speed penetration state. This study serves to promote the understanding of self-weight and negative pressure penetration mechanism for composite bucket foundation.

Study on Spatiotemporal Transport Characteristics of Soil Moisture in Layered Heterogeneous Vadose Zone Based on HYDRAS-3D

The heterogeneity of layered soils affects the transport processes of water in the vadose zone. However, the mechanism of soil moisture transport in the vadose zone under heterogeneous media conditions, especially the three-dimensional transport mechanism, is a frontier problem to be studied. In order to reveal the law of soil water transport in the vadose zone under heterogeneous media, this paper constructs a three-dimensional model of water transport using HYDRAS-3D (V 2.x) software through in situ tests of water transport in 3 × 3 × 4 m sample and verifies and analyzes the model. The vertical distribution and variability of soil water content and the temporal and spatial rules of soil water transversal transport at the soil–layer interface were analyzed. The results indicate that after adjusting the parameters in the HYDRAS-3D model using measured values, the simulation results are reasonable, and the model has high reliability. To represent the water content variability characteristics of the test tube profile, water movement in the vadose zone was classified as follows: (I) steady period (April–September, less affected by rainfall), (II) slow change period (January–March), and (III) rainfall rapid change period (June, when the impact of rainfall on the test cylinder was greater). The two largest values of the soil water potential variation gradient, 19.9 and 17.8 cm/d, were observed in the silty clay layer of the test cylinder, and the influence of evaporation and infiltration in the silty clay layer was most notable at the interface. The lateral transport of soil water at the interface was influenced to a certain degree by the layered heterogeneity, wherein the fine sand layer exhibited the most pronounced impact. This was followed by silt and silty clay layers, with the silt layer showing the lowest degree of influence. The research results can provide scientific reference for the rational planning of water resources in the Yinchuan Plain.

Distribution, sources, and health risk assessment of VOCs/SVOCs in soils obtained from petrochemical-contaminated sites in Guangzhou, a subtropical coastal megacity in southern China

Investigation and analysis of the soil contamination characteristics of legacy petrochemical sites is the basis for safe land reuse. Volatile/semivolatile organic compounds (VOCs/SVOCs) are a group of mutagenic, carcinogenic, and teratogenic substances that can induce leukemia, brain tumors, asthma, and a variety of other cancers through oral ingestion, dermal exposure, and/or inhalation. This study was designed to explore the horizontal and vertical distribution characteristics, sources, and health risks of VOCs/SVOCs in different operational areas of an abandoned petrochemical enterprise site in Guangzhou City. The survey assessed the presence and amounts of 12 VOCs/SVOCs across 522 soil samples. Measurements were conducted using a combination of purge and trap-gas chromatography and mass spectrometry (P&T-GC-MS). The investigation revealed that the total content of the 12 compounds was 69798.7 μg kg−1, with an average value of 5816.6 μg kg−1. The highest benzene content was 10900 μg kg−1, with an average value of 462.5 μg kg−1, and the maximum value exceeded this average by 2.7-fold. According to the horizontal distribution, VOCs/SVOCs were mainly concentrated in the oil delivery console, storage tank area, oil refining area, and fire pumping stations. Depending on the vertical distribution, pollutants were generally distributed in the plain fill layer, with a downward trend in the muddy silt and silt layers. The source apportionment of VOCs/SVOCs was analyzed and discussed with correlation analysis and a positive matrix factorization (PMF) model in this study. The source analysis results showed that a mixture of petroleum, solvent, and coal sources, solvent sources, and traffic sources were the main sources of VOCs/SVOCs, and their contribution rates to VOCs/SVOCs were 17.7%, 70.0% and 12.3%, respectively. The health risk assessment showed that 8 carcinogenic VOCs/SVOCs carry potential carcinogenic risks for children and adults. This study can provide data support and a judgment basis for the redevelopment of contaminated sites, determination of pollution responsibility and effective management of soil pollution.

Frost-induced changes in the structure of sediments – Results after 500, 1 000, 1 500 experimental freeze–thaw cycles

Sediment samples composed of silt (<0.063 mm), fine- (0.125–0.250 mm) and coarse-sand (0.5–1.0 mm) fractions were subjected to freeze–thaw cycles under controlled laboratory conditions for a period of eight months. A total of 40 samples of different sediment arrangement, sediment packing, water content and mineralization were studied at 0 (prior to experiment) and after 500, 1 000, and 1 500 freeze–thaw cycles. Macroscopic and 3-D X-ray imaging observations of the sediment structure reorganisation were reported. The results indicate modifications in the vertical and horizontal sediment arrangement along with the development of frost-induced deformational structures and internal (inter-layer) inhomogeneities of the sediment fabric. The most commonly observed changes in the sediment structure originated from the experimental frost action are: modifications at the boundary between lithologically-different sediments, formation of cracks within sediment layers, changes in thickness of the individual layers, and development of sediment deformations. The vast majority of frost-induced modifications of the sediment structure are observed within the silt layer and at its boundaries with sand layers. The presence and frost susceptibility of silt sediment may be treated as a driving force that facilitates the process of sediment deformation during the freeze–thaw activity. Moreover, it was shown that changes in the sediment structure include both formation and obliteration of frost-originated features with the increase in the number of freeze–thaw cycles.