The growth and evolution of sinkholes are a considerable proportion of the damage related to subsidence disaster in alluvial areas after ground water extraction for irrigation. In this research it was tried to study the evolution of the sinkholes from the birth point to the stabilization or final step. In the Eqlid-Abarkooh alluvial fan was selected an area about 300 km2 with giant sinkholes where consist; the city of Abarkooh, arable irrigated lands and desert rangelands. The major aspect on the study area was southwest to northeast where it ended to Abarkooh playa. For investigating the formation and evolution of these sinkholes in the study area, field observation for 2 years were done. Soil samples were taken from surface soils (0-25 cm) near and far of the sinkholes. Moreover, 4 soil samples were obtained from the deepest sinkhole as control sample in the study area. Chemical, physical and mechanical soil analyses were performed. Finally, the Ground Penetrating Radar (GPR) method were done for detection subsurface holes to depth of 4 m around the sinkholes. The chemical soil properties results include Electro Conductivity (EC) and the ratio of Ca2+/Mg2+ in lime which was important factors to formation of sinkholes changed from 2.05 to 19.3 dS/m, 0.15 to 6 respectively. The mechanical soil parameters such as Coefficient of Linear Extensibility (COLE) and Plasticity Index (PI) changed from 0.05 to 1.67, 0.99% to 15% respectively. According to sinkhole development, the results obtained that there was a relationship between diameter of sinkhole obtained from 0.6 to 15 m and groundwater extraction quantity changed from 0.18 to 18.14 m3/ha over 25 years. The groundwater level dropped 15 m and sinkhole volume variation obtained 0.014 to 2650 m3 over 25 years. Field discovery and google earth images showed that sinkholes were developed in 3 phases as (1) growth phase (2) mature and (3) steady phases up to about 25 years. The GPR results found some land breaks and a hole underground in the activation and growth phase of sinkhole evolution. Finally, according to some soil parameters and GPR results, the sinkhole hazard map was created in the study area.

The global impacts of agricultural land conversion on soil erosion and pollution, particularly in tobacco cultivation areas, are well-recognized as significant contributors to soil degradation. These areas are identified as hotspots for environmental concerns due to practices that lead to increased erosion and pollution. From this perspective, this case of study explores fine sediment samples from two areas with tobacco cultivation under different tillage systems and seasonal variations, transport into a headwater, and evaluates, on a local scale: (1) the impact of tillage systems on the geochemical signature of sediments; (2) if whether crop seasonality affects these sediment geochemical signatures. The Conventional Ridge Tillage (CRT) system involves extensive soil exposure and machinery for soil management, while the Mulch Ridge Tillage (MRT) system prioritizes soil conservation and relies on herbicides for weed control. The analytical methodology used to assess the sample element characteristics was Energy Dispersive X-ray Fluorescence (EDXRF). It was applied on the twenty fine sediments (ten of harvest and ten of inter-harvest season of tobacco) to quantitatively assess their inorganic composition. Additionally, Pearson correlation analysis, Hierarchical Cluster Analysis (HCA), and Principal Component Analysis (PCA) were applied on the EDXRF data to highlight the similarities and, thus, providing information to assess the complex data clustering patterns. As a result, the sediment compositions from the two studied soil systems are not similar. The PCA showed that the CRT sediments are characterized by the P, S, K, Ca, and Mn content, presenting a geochemical signature related to manure and fertilizer compared to the MRT, which is correlated with Al, Ti, Fe, Cu, and Zn contents, exhibiting a geochemical signature characterized by the natural soil composition. Therefore, the sediment geochemical signatures might be affected by two phases in the study area: a) tillage system characteristics and b) seasonal soil erosion. These findings underscore the importance of managing soil nutrients to mitigate soil pollution and nutrient exportation to aquatic systems. Moreover, the results emphasize the recommendations for sustainable agricultural practices in tobacco-growing areas to protect environmental quality.

This paper aims to develop geopolymer concrete (GPC) with flash-calcined soils cured under ambient conditions. Flash calcination is a heat thermal technique used to eliminate pollutants and organic content in excavated soils and allow them to be used in cementitious formulations. To develop GPC, the materials used in the development of the GP precursor binder should be rich in silicon (Si) and Aluminum (Al) that can react with alkaline silicates to yield Si-O-Al bonds that would form cementitious materials. The GP precursor binder is composed of Metakaolin (MK), flash-calcined soils, and granulated blast furnace slag (GBFS). The thermally treated soils are flash-calcined dredged sediments (FCS) and flash-calcined excavated clays (FCC) while potassium silicate is used as the alkaline reagent. This study aims to use the materials above to develop GPC cured under ambient conditions with high strength, good durability, and microstructure properties. Seven formulations are done to evaluate the effect of replacing MK with either FCS or FCC and GBFS on the mechanical compressive strength, water absorption, and freeze-thaw test. The findings reveal that using only metakaolin (MK0) in the formulation yielded the highest compressive strength. These results align with the porosity test outcomes, which show correlations between micropore and macropore percentages. Analysis of the durability freeze-thaw test suggests that as the proportion of macropores increases, formulations incorporating FCS and FCC exhibit improved resistance to extreme temperatures. Conversely, an increase in GBFS content leads to a finer microstructure and reduced resistance. Water absorption testing indicates that formulations with FCS and FCC display favorable sorptivity coefficients compared to MK0, with increased GBFS content enhancing durability. SEM/EDS and calorimetry tests were conducted to investigate the impact of substituting FCS and FCC for MK within the geopolymer matrix.

The excellent grounding performance of tracked mining vehicles (TMVs) is a crucial foundation for the normal operation of the entire deep-sea polymetallic nodule mining system. Based on the weak mechanical properties of deep-sea fluidized sediments, this study conducted model tests to deeply analyze the pressure-sinkage relationship curve characteristics and the soil failure process under the vertical action of the TMV track plates. It identified the influence of soil water content on the failure mode and compaction degree and established a new segmented pressure-sinkage model, verifying its accuracy. The test results showed that the width of the track plates and the water content of the sediments had a significant impact on the pressure-sinkage relationship curve, while the sinkage speed had little effect. The bearing capacity of the sediment was an inherent property of the soil, independent of the track plate width and sinkage speed, and decreased with increasing water content. By combining the changes in soil strength and the movement characteristics of soil particles under vertical load, the pressure-sinkage model was divided into the compaction stage, elastic stage, elastoplastic stage, and plastic stage. Based on the experimental results under various conditions, a predictive model for track sinkage depth that considers sediment water content and track plate width was developed. The findings of this study can provide a scientific theoretical basis for the design optimization of parameters such as vehicle weight and track dimensions, promoting the development of deep-sea polymetallic nodule mining.

Sandy hydrate reservoirs are considered an ideal target for the extraction of marine natural gas hydrates (NGH). However, engineering geological risks, including reservoir sand production and seabed subsidence during the extraction process, present a significant challenge. In 2019, China discovered a high-concentration sandy NGH reservoir with favorable commercial development potential in the Qiongdongnan Basin of the South China Sea, establishing the region as a key focus for future exploration and development efforts. A thorough comprehension of macro-meso mechanical properties of this specific sandy NGH reservoir is essential for the safe and efficient extraction of hydrates. In this study, a novel method is proposed to calculate hydrate saturation of hydrate-bearing sandy sediments (HBSS) with hexagonal close-packed state. A series of undrained biaxial compression with flexible boundary show that hydrate cementation enhances the strength of the sample. However, an excessively high hydrate saturation is likely to induce strain softening, whereas an increase in confining pressure helps to mitigate strain softening. Hydrate cementation promotes the formation of abundant force chains. The inhomogeneous displacement, sliding, and relative rotation of the particles are the primary factors contributing to the formation of X-shaped shear bands, which is related to cemented bond breakage. The primary cause of hydrate cementation failure is tensile stress failure. External loading induces force chains to undergo buckling, fracturing, and restructuring, which governs fabric development. The research outcomes offer novel insights into the inhomogeneous deformation and macro-meso mechanical properties of HBSS at the particle-scale.

In the long-term exploitation of natural gas hydrate, the stress change intensifies the creep effect and leads to the destruction of pore structures, which makes it difficult to predict the permeability of hydrate reservoir. Although permeability is crucial to optimize gas recovery for gas hydrate reservoirs, until now, accurately modeling the permeability of hydrate-bearing clayey-silty sediments during the creep process remains a significant challenge. In this study, by combining the nonlinear fractional-order constitutive model and the Kozeny-Carman (KC) equation, a novel creep model for predicting the permeability of hydrate-bearing clayey-silty sediments has been proposed. In addition, experimental tests have been conducted to validate the derived model. The proposed model is further validated against other available test data. When the yield function F 0, the penetrating damage bands will be generated. Results show that, once the model parameters are determined appropriately by fitting the test data, the model can also be used to predict permeability under any other stress conditions. This study has a certain guiding significance for elucidating the permeability evolution mechanisms of hydrate-bearing clayey-silty sediments during the extraction of marine gas hydrates. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Permafrost thaw has the potential to release ancient particulate and dissolved organic matter that had been stored for thousands of years. Previous studies have shown that dissolved organic matter from permafrost is very labile and can be used by heterotrophic microbes close to the thaw area. However, it is unknown if ancient particulate organic matter can also be utilized. This study aims to investigate whether arctic microbial communities (bacteria and Archaea) incorporate ancient organic matter potentially released from thawing permafrost into their biomass. We compare and contrast the radiocarbon signatures of microbial lipids and higher plant biomarkers (representing terrestrial organic matter) from five soil profiles and seven deltaic lake sediment cores from the Mackenzie River drainage basin, Arctic Canada. In the surface soils, modern to post-modern short-chain fatty acids (SCFA) ages indicate in situ microbial production, with differential rates of organic carbon (OC) cycling depending on soil moisture. In contrast, SCFA in deeper soils display millennial ages, which likely represent the microbial necromass preserved through mineral association. In deltaic lakes that are disconnected from the river, generally old SCFA suggests the uptake of pre-aged OC by bacteria. In perennially connected lakes, pre-aged SCFA could originate from in situ microbial uptake of old OC or from the Mackenzie River. Higher plant-derived long-chain fatty acids (LCFA) present older radiocarbon ages, reflecting mineral stabilization during either pre-aging in soils (for high closure lakes) or riverine transport (for no and low closure lakes). Archaeal lipids are younger than SCFA and LCFA in high closure lakes, and older in low and no closure lakes, mirroring bulk radiocarbon signatures due to their heterotrophic production. These radiocarbon signatures of bacterial biomarker lipids may therefore reflect microbial incorporation of ancient OC (e.g., derived from permafrost thaw) or exceptional preservation (e.g., through mineral stabilization). Hence, even in relatively high OC environments such as arctic aquatic ecosystems, microbes can rely on ancient OC for their growth.

The mechanical behavior of Methane Hydrate-Bearing Sediment (MHBS) is essential for the safe exploitation of Methane Hydrate (MH). In particular, the pore size and physicochemical characteristics of MHBS significantly influence its mechanical behavior, especially in clayey grain-cementing type MHBS. This study employs the Distinct Element Method (DEM) to investigate both the macroscopic and microscopic mechanical behavior of clayey grain-cementing type MHBS, focusing on variations in pore size and physicochemical characteristics. To accomplish this, we propose a Thermo-Hydro-Mechanical-Chemical-Soil Characteristics (THMCS) DEM contact model that incorporates the effects of pore size and physicochemical characteristics on the strength and modulus of MH. This THMCS model is validated using experimental data available in the literature. Using the proposed contact model, we conducted a series of investigations to explore the mechanical behavior of MHBS under conventional loading paths, including isotropic and drained triaxial tests using the DEM. The numerical results indicate that smaller pore sizes and lower water content-key physicochemical characteristics resulting from variations in electrochemical properties and the intensity of the electric field-can lead to reduced shear strength and stiffness due to the increased breakage of aggregates and weakened cementation. Additionally, heating was found to further accelerate the process of structural damage in MHBS.

The efficiency of alkali-activated ground granulated blast furnace slag in stabilizing dredged sediments with high water contents is suboptimal because the activators become diluted. To improve stabilization efficiency, additives such as nano-CaCO3 are proposed. However, some of the proposed additives may not be practical owing to their high costs. This study experimentally investigates the addition of Na2CO3 for the stabilization of dredged sediment with high water contents (i.e., 100%) using Ca(OH)2-activated slag. Experimental results show the optimal content of Na2CO3 to obtain the highest 28-day unconfined compressive strength of stabilized sediments is 0.2% gravimetrically. Below the optimal content, the strength increases with Na2CO3 content. Above the optimal content, a decrease in strength is observed. By examining the reaction products and microstructure of the stabilized dredged sediments, it is observed that the coupling mechanism of cation exchange and calcite precipitation promotes the development of finer capillary pores, leading to a reduction in interpore connectivity and lower structural heterogeneity of the fine capillary pores. Experimental evidence from this study broadens the practical applications of sustainable soil stabilization using additives.

This study investigates the sustainable use of seabed dredged sediments and water treatment sludges as construction materials using combined dewatering and cement stabilization techniques. Dredged sediments and water treatment sludges, typically considered waste, were evaluated for their suitability in construction through a series of dewatering and stabilization processes. Dewatering significantly reduced the initial moisture content, while cement stabilization improved the mechanical properties, including strength and stiffness. The unconfined compressive strength (UCS), shear modulus, and microstructural changes were evaluated using various analytical techniques, including unconfined compression testing, free-free resonance testing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results show a direct correlation between reduced w/c ratios and increased UCS, confirming the potential of treated sludge as a subbase layer for roads and landfill liners. A chemical analysis revealed the formation of calcium silicate hydrate (CSH) and ettringite, which are critical for strength enhancement. This approach not only mitigates the environmental issues associated with sludge disposal but also supports sustainable construction practices by reusing waste materials. This study concludes that cement-stabilized dredged sediments and water treatment sludges provide an environmentally friendly and effective alternative for use in civil engineering projects.