Seasonal freezing and thawing significantly influence the migration and distribution of soil hydrothermal salts. Understanding the dynamics of hydrothermal salt forces in canal foundation soils is crucial for effective canal disease control and optimization. However, the impact on rectangular canals remains poorly understood. Therefore, field-scale studies on water-heat-salt-force-displacement monitoring were conducted for the canal. The study analyzed the changes and interaction mechanisms of water-heat-salt-force in the soil beneath the canal, along with the damage mechanisms and preventive measures. The results indicate that the most rapid changes in temperature, moisture, and salt occur in the subsoil on the canal side, with the greatest depth of freezing. Heat transfer efficiency provides an intuitive explanation for the sensitivity of ground temperature at the junction of the canal wall and subsoil to air temperature fluctuations, as well as the minimal moisture migration in this region under the subcooling effect. The temperature-moisture curve suggests that current waterheat-force and water-heat-salt-force models exhibit a delay in accurately predicting water migration within the subsoil. Rectangular canals are more susceptible to damage under peak freezing conditions, requiring a combined approach of freezing restraint and frost-heaving force to mitigate damage. These findings offer valuable insights for canal design, maintenance, and further research.

Thermochemical processing of biowaste generates renewable carbon-rich materials with potential agronomic uses, contributing to waste valorization. This study evaluates the application of hydrochar obtained from hydrothermal carbonization of food waste, those obtained by different post-treatments (washing, aging, and thermal treatment), as well as biochar obtained by pyrolysis as soil amendments. For this purpose, the effect of char addition (1-10 wt% d.b.) on a marginal agricultural soil on germination and growth of Solanum lycopersicum (tomato) plants was assessed. All the hydrochars exhibited a chemical composition suitable for agronomic use, characterized by high nutrient content, abundant organic matter, and low concentration of phytotoxic metals. In contrast, biochar exceeded the permissible limits for Cr, Cu, and Ni concentrations rendering it unsuitable for application to agronomic crops. The high temperature of thermal post-treatment and pyrolysis favored mineral and heavy metal concentration while washing significantly reduced nutrient content (N, S, P, K, Mg) along with the electrical conductivity. The addition of biochar or both washed and thermally post-treated hydrochar negatively affected tomato growth. Reduced chlorophyll content was associated with the decreased expression of genes encoding enzymes involved in antioxidant metabolism. This led to photosynthetic membrane damage, as evidenced by chlorophyll fluorescence-related parameters. Conversely, the addition of aged (<= 5 wt %) and fresh (1-10 wt%) hydrochars increased both germination and plant growth compared to unamended soil, indicating that hydrochar from food waste does not require additional post-treatments to be used as a soil amendment.

In the context of global warming, understanding the impact of thaw slump on soil hydrothermal processes and its responses to climate is essential for protecting engineering facilities in cold regions. This study aimed to investigate the effect of thaw slump development on active layer soil. We considered the early thaw slump development in the Tibetan Plateau as research object and conducted long-term monitoring of soil hydrothermal activity in the active layer of various parts of the landslide and the regional meteorology. The results showed that thaw slump development shortened the freezing and thawing time of the active layer, increased the freezing and thawing rates of the shallow soil (10-20 cm), and enhanced the heat exchange between the active layer soil and the atmosphere and the heat transfer between the soils. The heat-exchange efficiency of the active layer, from largest to smallest, was headwall > collapsed area > unaffected area (bottom of the slope) > unaffected area (top of the slope). Furthermore, thaw slump development lowered the water storage of the active layer prof ile and weakened the dynamic response of soil water to precipitation. The events of soil water responses and soil water increments were smaller in the landslide area than in the unaffected area. During a co-precipitation event, the overall soil water storage increment (SWSI) of the profile was significantly smaller in the landslide area than in the unaffected area (P < 0.05), with an SWSI of 2.04 mm in the headwall and 1.77 mm in the collapsed area. In addition, thaw slump development altered the mechanism of soil water transport driven by soil temperature changes, which affected soil water redistribution of profile. The study gives ecohydrology-related research in cold climates a scientific foundation, thereby guiding the construction and maintenance of infrastructure projects.

Mechanical alterations in shale formations due to exposure to water-based fracturing fluids and supercritical carbon dioxide (ScCO2) significantly affect the performance of shale gas exploration and CO2 geo-sequestration. In this study, a hydrothermal (HT) reaction system was set up to treat Longmaxi shale samples of varying mineralogies (carbonate-, clay-, and quartz-rich) with different fluids, i.e. deionized (DI) water, 2% potassium chloride (KCl) solution, and ScCO2 under HT conditions expected in shale formation. Statistical micro-indentation was conducted to characterize the mechanical property alterations caused by the shale-fluid interactions. An in situ morphological and mineralogical identification technique that combines scanning electron microscopy (SEM) and backscattered electron (BSE) imaging with energy-dispersive X-ray spectroscopy (EDS) was used to analyze the microstructural and mineralogical changes of the treated shale samples. Results show no apparent changes in the Young's modulus, E, and hardness, H, after treatment with DI water under room temperature (20 degrees C) and atmospheric pressure for 7 d. In contrast, E and H were decreased by 31.2% and 37.5% at elevated temperature (80 degrees C) and pressure (8 MPa), respectively. The addition of 2% KCl into DI water mitigated degradation of the mechanical properties. Quartz-rich shale specimens are the least sensitive to the water-based fracturing fluids, followed by the clay-rich and carbonate-rich shale formations. Based on in situ morphological and mineralogical identification, the primary factors for the mechanical degradation induced by water-based fluids include carbonate dissolution, clay swelling, and pyrite oxidation. Slight increases in the measured E and H and compression of porous clay aggregates were observed after treatment with ScCO2. The major factor contributing to the mechanical changes resulting from the exposure to scCO2 appears to be the competition between swelling caused by adsorption and compression of shale matrix. (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/).

The moisture accumulation and freezing damage of coarse-grained fill (CGF) in high-speed railway (HSR) subgrades have been widely concerned. Based on the newly developed water-vapor-heat-mechanical coupling test apparatus, a series of soil column tests were carried out to investigate the frost heave mechanism of CGF. The results indicate that the liquid water in CGF is discontinuous and difficult to migrate to the freezing front. The primary mechanism of moisture accumulation and frost heave in CGF is vapor migration and phase transition. With increasing freeze-thaw cycles, both vapor migration and frost heave reduce. The thaw settlement of the CGF is less than the frost heave, so there is a net upward deformation in each cycle. Furthermore, the fine particle content has a prominent effect on the heat transfer and frost heave of the CGF compared to the fine particle type. Even under the condition of vapor replenishment, controlling the content of fine particles is still an important way to inhibit frost heave. Moreover, after reducing the maximum particle size of CGF, the frost heave of the sample increases. Nuclear magnetic resonance (NMR) test results show that CGF is dominated by large pores, and the freeze-thaw cycle further promote the development of large pores, providing a good channel for the migration of vapor. In conclusion, the frost heave development caused by vapor migration is slow and continuous, posing a non-negligible risk to HSR subgrades during long-term service.

Southwest China was affected by two extreme droughts in the autumn to spring of 2012-2013 and the winter to summer of 2020-2021. These droughts caused water depletion, crop damage, and socio-economic disruption. However, little is known about the accurate representation of the two drought events and the responses of vegetation to the droughts. We used multiple vegetation indices and multi-source climate data to quantify the spatiotemporal variations of the two events. We assessed the different responses of vegetation greenness in Southwest China to the two drought events to determine the underlying mechanisms. Vegetation greenness in Southwest China showed different responses to the two events due to differences in the early hydrothermal conditions. The 2012-2013 autumn-spring drought suppressed vegetation growth in Southwest China, with a total decrease of 0.17 (31.7 %) in the normalized difference vegetation index relative to the baseline conditions in the early stage of the drought. The decrease in precipitation and soil water depletion in late summer 2012 aggravated the decrease in vegetation greenness from winter 2012 to spring 2013. By contrast, during the winter-summer drought in 2020-2021, there was an increase of 0.22 (52.3 %) in the normalized difference vegetation index in January-March 2021 relative to the baseline conditions. Adequate precipitation and soil water in the late summer to autumn of 2020 compensated for water loss due to the extreme drought, and, concurrently, more downward solar radiation and warmer conditions linked to less cloudiness contributed to vegetation greening in spring 2021. These results show that early hydrothermal conditions have a vital role in the different responses of vegetation greenness to extreme drought events. These results will help in water management and ecosystem protection in the current background of more frequent extreme weather and climate events resulting from the global climate crisis.

Hydrothermal solidification offers an effective, sustainable method for stabilizing clay soil, addressing environmental concerns while improving geotechnical properties. Facilitating pozzolanic reactions between lime and clay under controlled temperature and pressure significantly enhances compressive strength and soil durability. This process promotes calcium silicate hydrate (C-S-H) formation, reduces industrial waste, and supports lime reuse, making it an energy-efficient soil improvement approach. This study investigates the impact of lime addition (0-20%) and various chemical and physical parameters on clay soil compressive strength. Key chemical components include SiO2 (20.1-76.9%), Al2O3 (7.6-34.8%), Fe2O3 (0.6-32.9%), CaO (0.1-43.5%), MgO (0-9.56%), Na2O (0.01-2.8%), and K2O (0.1-3.9%). Physical properties such as density, plasticity index (6-34.5%), and liquid limit (24-65.2%) were analyzed alongside process parameters like heating temperature (60-1000 degrees C), curing time (0-120 days), and curing temperature (20-41 degrees C). Using a dataset of 152 samples divided into training and testing groups, the statistical analysis focused on the leaching coefficient (Lc) and silica-sesquioxide ratio (Kr). Lc emerged as the most significant factor, achieving an R2 of 0.89 and an RMSE of 1.13 MPa. This study found that the compressive strength of lime-treated clay soils varied from 0.02 MPa to 11.9 MPa, influenced by lime concentration, chemical composition, and processing factors. Increased lime additions, particularly when combined with hydrothermal treatment, led to significant strength enhancements owing to improved pozzolanic activity. The plasticity index (PI) markedly diminished with lime stabilization, enhancing workability and mitigating volumetric variations. The density of treated soils rose from 0.8 g/cm3 to 2.1 g/cm3, signifying improved particle compaction and less porosity. The mechanical enhancements indicate that hydrothermal solidification efficiently converts expanding clay into a robust and stable material appropriate for geotechnical applications. Increased Lc improved compressive strength through enhanced pozzolanic activity and density, while higher Kr values, indicating lower CaO availability, yielded limited strength gains. Lc consistently outperformed Kr and other chemical compositions in enhancing clay soil compressive strength.

Under the action of freeze-thaw cycles, the internal temperature and water distribution of slope soils in cold regions change significantly, which directly affects the stability of slopes. In order to study the differences in hydrothermal reactions at different depths and their impacts on the stability of slopes. This study establishes both a freeze-thaw model and a hydrothermal coupling model, combining field measurements with numerical simulations to examine the dynamic changes in hydrothermal characteristics within the slope. The results indicate that the variation in slope temperature with depth can be divided into three stages: initial freezing, stable freezing, and thawing. In the freezing stage, the negative temperature gradient drives water to migrate towards the freezing front, forming segregated ice and inducing frost heave. In the thawing stage, the latent heat released by the phase change in segregated ice promotes water to move towards the slope toe, increasing the water content there and indirectly exacerbating the risk of slope instability. The heat and moisture transfer in frozen soil slopes shows non-linear and dynamic characteristics. The unique process of one-way freezing and two-way thawing makes the thawing rate 1.35 times that of the freezing rate, and this asymmetric characteristic is the key to understanding the mechanism of slope instability.

The fill-cut transition subgrade (FCTSS) is a weak point in subgrade damage. Indoor experiments were conducted to clarify the deformation damage mechanism. It was found that repeated dynamic load leads to upward migration of moisture along the fill-tangent interface and the formation of moisture migration channels. The overall moisture of the soil samples increased under the condition of continuous moisture migration and aggregation. The increase in moisture weakened the strength of the soil, resulting in an increase in moisture accumulation in the region corresponding to the location of greater compressive deformation, which is also the location where damage occurred. Therefore, in order to prevent the effect of dynamic load on the deformation damage of the subgrade, the external recharge of FCTSS should be controlled. This study can provide a valuable reference for the construction and protection of subgrade in the fill-cut transition in loess areas.

In order to reveal the effect mechanism of hydrothermal aging on jute fiber (JF)-reinforced waterborne acrylic resin (WAR) composites and broaden the application of JF in the field of composites, JF/WAR composites were prepared in this paper to explore the impact mechanism of hydrothermal aging on the flexural properties and volatile organic compound (VOC) release of composites. The results showed that the atomic kinetic energy increased with increasing temperature at 25 degrees C, 40 degrees C and 60 degrees C, and the diffusion coefficient increased by 476.88 % at 60 degrees C. The weight loss rates were 1.53 %, 2.71 %, and 5.07 %, respectively. The weakening of the CO peaks, O-H peaks as well as C--O proved the degradation of JF and WAR. The flexural strength of the samples decreased to 63.43 MPa, 59.87 MPa, and 42.88 MPa with increasing temperature at 25 degrees C, 40 degrees C and 60 degrees C, respectively, and the flexural modulus was more sensitive to hydrothermal aging. Under short-term hydrothermal aging conditions, the composites all complied with Fick law. Water molecules diffuse, adsorb and dissolve hydrophilic VOC molecules in the pores of the composite materials. Non-Fick diffusion behaviors occurred under long-term hydrothermal aging conditions, and serious damage occurred at the interface of the fiber matrix, with fiber breakage as the main damage mode, and the transmission resistance of VOC will decrease after 1440 mins hydrothermal aging, and the release of VOC will increase significantly.