Talus slopes and scree deposits connect rockwall sediment supply, gravitational transport, footslope storage, hydrothermal conditions, and mountain hazards, yet their literature is distributed across several disciplines. This study develops a manually refined bibliometric dataset to clarify the knowledge structure and thematic evolution of talus slope geomorphology. We retrieved 971 records from the Web of Science (WoS) Core Collection, including the Science Citation Index-Expanded (SCI-EXPANDED) and Social Science Citation Index (SSCI) databases, manually screened their geomorphic relevance, excluded records from the incomplete publication year 2026, and analyzed 548 articles and reviews published during 1966–2025. Bibliometrix and Biblioshiny analyses show sustained publication growth, especially after 2006, and an intellectual base combining slope-process geomorphology, paraglacial and periglacial research, geophysical investigation, and hazard studies. Standardized Author Keywords indicate increasing attention to permafrost environment, subsurface detection, multi-source monitoring, and slope hazards. These indexed patterns support a synthesis of talus slopes as dynamic source-transport-storage systems, while the WoS-only coverage and manual refinement steps define the study’s evidential limits.

The Qinghai-Xizang Highway (QXH) exhibits widespread pavement damages because of underlying permafrost thawing. To comprehensively reflect the pavement damages and their controlling factors, images were processed and compared from ground penetrating radar (GPR) and unmanned aerial vehicle (UAV) in 7 typical sections along the QXH in the permafrost regions. The field monitoring data of ground temperature, embankment deformation were also collected to jointly investigate distribution, formation process and development mechanisms of roadway distress based on multi-source data. Indices such as distress ratio, pavement roughness and lateral deformation of the QXH were calculated by image segmentation and spatial analysis based on the UAV images. Results showed that (1) the temporal-spatial distribution of standard deviation of pavement altitude from the UAV image can quantitatively reflect the pavement roughness caused by embankment settlement and and vehicle loading during the roadway operation. The standard deviation has the maximum of difference of with 20-30 cm/a. (2) The average lateral deformation of the QXH can be extracted from the UAV image in thick embankment sections, which was 0.09 m/a in 4 of the 7 selected sections (K3059, K3119, K3177 and K3188). (3) Field monitoring data revealed the climate warming and permafrost thawing along the QXH. The GPR results and the UAV image can mutually verified for the explanation for the formation and development of the pavement damages. The findings can provide a comprehensive analysis method for the pavement damage and embankment distress based on multi-sourced data, and scientific guide for distress prediction and roadway maintenance.

Frost heave poses a critical threat to the stability of infrastructure built on or within frozen ground. Although coarse-grained soils are generally considered less susceptible to frost heave due to their high permeability, low capillarity, and limited water retention, field observations suggest that under specific hydrogeological conditions, such soils can still experience significant frost heave. This study investigates the role of hydraulic pressure in initiating ice growth in freezing coarse materials, using sand as a representative material. Several 1D freezing tests were conducted using a custom-designed apparatus capable of simulating water recharge under hydraulic pressure. Experimental evidence indicates that the presence of hydraulic pressure notably accelerates ice lens growth, even in soils typically classified as non-frost heave susceptible. A model incorporating external water migration via unfrozen water films was developed, revealing that hydraulic gradients enhance water migration toward the ice lens via film, thus accelerating ice segregation. These findings suggest that conventional soil-replacement method employed in cold regions engineering may not be entirely effective if subjected to hydraulic pressure. Overall, this work challenges traditional assumptions regarding the frost heave resistance of coarse-grained soils and highlights the importance of incorporating hydrogeological factors into the frost-prone engineering design. The study also provides a theoretical and experimental basis for frost damage mitigation in cold-region infrastructure.

Accurate estimation of the runoff onset date (ROD) is critical for water resource management and the assessment of snowmelt-related hazards. Currently, remote sensing retrieval of ROD primarily relies on the backscatter of synthetic aperture radar (SAR). However, when using SAR data for ROD estimation in forested areas, microwave signals are severely attenuated due to scattering and reflection from branches and tree trunks, making it difficult to capture the state changes of snow beneath the forest canopy. Considering the strong correlation between ROD and vegetation phenology, this study proposes a machine learning-driven framework that leverages Extreme Gradient Boosting (XGBoost) to enhance the accuracy of ROD estimation in forested areas through the synergistic fusion of multi-source heterogeneous data. The model integrates 20 spatiotemporal features, including SAR backscatter, vegetation index, air temperature, and geospatial data. Focusing on California, USA, as the study area, we extracted eight SAR features from 3,925 Sentinel-1 images, four vegetation phenological features from 207 MODIS images, and three meteorological features from ERA5-Land hourly temperature data for the period February to July 2017-2025. Additionally, five geospatial features were derived from Copernicus DEM (GLO-30) and ESA WorldCover datasets. The model was trained and validated against ground-truth ROD data from 125 snow water equivalent (SWE) stations over nine years, yielding a total of 850 samples, using station-grouped 5-fold cross-validation. The results show that the XGBoost ensemble model incorporating spatiotemporal features achieves higher accuracy compared to RF, SVM, LightGBM, MLP, and MLR, with R, MAE, and RMSE reaching 0.63, 10.60 d, and 15.08 d, respectively. When analyzed separately by land cover type, XGBoost yielded the best accuracy among forest stations (R = 0.63, MAE = 10.81 d, RMSE = 15.26 d), whereas RF achieved the highest performance at non-forest stations (R = 0.67, MAE = 9.16 d, RMSE = 13.70 d). Stability analysis indicates no significant variance in MAE across different latitudes, elevations, aspects, or years (p>0.05), confirming the model's robustness. Designed for the historical monitoring of snowmelt, this model enables accurate large-scale estimation of ROD in forested areas under complex mountainous terrain for the first time.

Degrading permafrost beneath the embankment of the Qinghai-Tibet Highway (QTH) induces embankment settlement, which often leads to subgrade damage and disrupts normal highway operation. Based on the ground temperatures and embankment deformation at six monitoring sites, five in permafrost regions and one in a talik region, collected from 1998 to 2020, characteristics of permafrost degradation and embankment deformation were first analyzed. Beneath the embankment centerlines, permafrost thawing rates ranged from 9.7 to 19.9 cm/ a, while the permafrost warming rates at 15.0 m depth varied from 0.005 to 0.019 degrees C/a during the monitoring period. Subgrade deformation was dominated by settlement, with rates of 0.4 to 4.4 cm/a. Three typical forms of embankment deformation are summarized to roughly indicate the general deformation trends. Significant settlement can persist for a long period due to the slow consolidation of the thawed permafrost. Transverse differences in embankment settlement were caused by asymmetric permafrost thawing rates beneath the left and right shoulders. Overall, the evolution of embankment settlement was mainly controlled by the process of permafrost degradation. The results improve understanding of the relationship between permafrost degradation and embankment deformation and provide valuable guidance for the design, construction and maintenance of highways in permafrost regions.

Compacted loess exhibits significant degradation in its engineering properties after undergoing freeze-thaw (F-T) cycles, posing a substantial disaster risk under dynamic loading. However, the dynamic characteristics of post-F-T loess and the physical mechanisms governing these changes remain unclear. This study investigated compacted loess specimens with varying moisture contents. A series of laboratory tests, including F-T tests, dynamic triaxial tests, and scanning electron microscopy tests, was conducted to determine the influence of F-T cycles and moisture content on the dynamic stress versus dynamic strain (sigma d-epsilon d) relationship, dynamic shear modulus, and damping ratio of compacted loess. The mesostructural evolution characteristics of compacted loess with different moisture contents under F-T cycles were analyzed. The dynamic deformation mechanism of compacted loess with high water content was explored. The results suggest that the sigma d-epsilon d relationship of the post-F-T cycles compacted loess conforms to the Hardin-Drnevich model. The initial moisture content of the specimens significantly influenced the dynamic stiffness and profoundly affected the microstructure of the compacted loess. After the F-T cycles, the structural compactness of the compacted loess with a moisture content of 9.6% initially increased and subsequently decreased. The dynamic shear modulus increased and reached its peak value in seven F-T cycles and then declined with increasing F-T cycles, whereas its damping ratio initially decreased and then increased. The structures of the compacted loess specimens with moisture contents of 14.6% and 20.6% tended to loosen. The dynamic shear modulus decreased continuously with increasing F-T cycles, whereas the damping ratios increased continuously. Under long-term F-T cycles (greater than or equal to 15 F-T cycles), the dynamic shear modulus of the loess with a moisture content of 20.6% exhibited a rebound and increase, coupled with a decrease in the damping ratio.

Under the background of global climate changing, the warming of permafrost has led to numerous engineering infrastructures being operated on warm permafrost foundations with diminishing bearing capacity. Meanwhile, infrastructure construction not only increases the overburden load on permafrost foundations but also induces directional deviation of the principal stress axis relative to the vertical direction. Therefore, conducting study on the stress-strain behavior and strength characteristics along different principal stress directions in warm frozen soils is imperative for accurately assessing deformation evolution patterns and bearing capacity of warm permafrost foundations. Thus, the stress-strain relationships respond, non-coaxiality evolution and strength distribution characteristics during directional loading along different principal stress directions were systematically investigated. The results indicated that the influence of principal stress direction on the strength intensifies with decreasing initial mean principal stress (when p0 = 500 kPa, the strength at alpha = 45 degrees exhibits a 27.3 % reduction compared to the alpha = 0 degrees). Concurrently, increasing initial mean principal stress diminishes both the stress-strain non-coaxiality angle and the directional dependence of strength. Furthermore, a novel strength model incorporating principal stress direction is proposed for warm frozen silt. These findings elucidate the correlation mechanisms between non-coaxiality evolution and strength anisotropy in warm frozen silt under fixed principal stress direction, providing theoretical foundations for optimizing engineering designs in permafrost regions under warming scenarios.

Retrogressive thaw slumps (RTSs) rapidly reshape microtopography and near-surface structure on permafrost hillslopes, altering infiltration pathways, hillslope–channel hydrologic connectivity, and subsurface heat–water exchange. However, point observations remain insufficient to resolve hydrothermal heterogeneity and near-zero temperature-zone processes at the profile scale. Here, using a representative RTS site in the northeastern Qinghai–Tibet Plateau (QTP), we develop a monitoring-constrained ground-penetrating radar (GPR) framework for profile-scale hydrothermal inversion. Stratified monitoring data from an undisturbed reference area are used to establish relationships among relative permittivity, temperature, and volumetric water content, which are then applied to multi-temporal GPR profiles to reconstruct two-dimensional temperature and water-content fields. The temperature inversion retains high accuracy near phase transition, with an RMSE of 0.219 °C. The reconstructed profiles reveal clear seasonal contrasts in the near-zero temperature zone, with areal proportions of 0.482–0.485 in early July and 0.738–0.744 in late October. Among the late-October profiles, the mean depth of the 0 °C isotherm varies little, whereas its lateral roughness ranges from 0.114 to 0.135 m, indicating stronger lateral thermal heterogeneity. At the slump head, shallow mean water content differs little among profiles, but wet-zone occupancy differs by 14.7 percentage points at a water-content threshold of 0.35 and nearly doubles at 0.40. These results show that structural metrics provide more sensitive profile-scale constraints for interpreting subsurface water redistribution and heat-transfer processes under RTS disturbance, thereby providing a useful reference for assessing hydrothermal reorganization in degrading permafrost landscapes.

Rock glaciers are important geomorphic indicators of mountain permafrost conditions, yet the mechanisms controlling spatially heterogeneous deformation within individual rock glaciers remain poorly understood. This study investigates the Baishuigou Rock Glacier (BRG) in the Qilian Mountains by integrating multi-year InSAR observations, borehole stratigraphic data, and ground-temperature measurements to characterize its deformation and explore its relationship with permafrost degradation. The results reveal pronounced spatial heterogeneity in surface displacement. The main body of the rock glacier exhibits persistent displacement, with mean annual LOS displacement rates ranging from −6.93 to 13.19 mm yr−1, corresponding to relatively well-preserved ice-rich frozen ground. The frontal zone shows stronger and more variable displacement under more degraded subsurface conditions, whereas the relict rock glacier area exhibits relatively weak displacement dominated by seasonal thermal responses. Comparisons among the borehole sites further indicate that spatial differences in surface displacement correspond to variations in active-layer thickness, ground-ice conditions, and thermal state. The integrated observations suggest a possible spatial transition from relatively well-preserved ice-rich frozen ground in the upper part of the rock glacier toward more degraded conditions downstream. This study demonstrates that integrating surface deformation with subsurface structural and thermal observations provides stronger physical constraints for understanding spatially heterogeneous rock glacier deformation and its relationship with frozen-ground conditions.

Extreme weather events, including heatwaves, cold waves, and strong winds, significantly impact lake thermal stratification and aquatic ecosystem stability. This study applied the Environmental Fluid Dynamics Code (EFDC) hydrodynamic-thermal model to analyze the thermal stratification characteristics of Lake Fuxian and its response to extreme weather. The results indicate that the stratification period spans from March to December, with the mixed layer depth (MLD) varying between 6.86 m and 9.89 m in spring and summer, and deepening to 47.7 m in autumn and winter. Extreme heat compresses the MLD and increases surface temperature by 1.59 °C, while strong winds deepen the MLD, causing cooling at the surface and warming at greater depths. Cold waves slightly reduce the mixed-layer temperature and weaken the thermocline. Air temperature, solar radiation, and wind-driven turbulence jointly control the vertical temperature distribution, with wind-driven circulation playing a key role in surface temperature heterogeneity. These findings highlight the need for adaptive management strategies, such as adjusting water intake depths during heatwaves and enhancing monitoring during extreme weather events, to protect aquatic ecosystems under climate change.

Driven by rapid climate change and accelerated glacial recession, many proglacial forefields have recently evolved into complex ice-debris landforms exposed to periglacial environments. These transitional processes have significant implications for geomorphological evolution and water supply in arid high-mountain regions; however, our understanding of the thermal mechanisms governing their evolution and long-term stabilization remains limited. This study evaluates the thermal evolution and heat transfer regimes at a retreating glacier margin in the Aerzailaikunai Valley in the eastern Tianshan Mountains in China based on the results of in-situ observations and measurements (ground temperature monitoring, pit excavation, and microclimatic measurements). The results indicate that as elevation decreases, the debris cover of the retreating glacier margin transitions from thin (less than 20 cm) and fragmented layers to thick (56–148 cm) and spatially continuous layers that fundamentally alter the subsurface thermal state. This thickened debris cover facilitates a pronounced thermal asymmetry within the active layer, characterized by a rapid autumnal freezing rates (7.71–7.85 cm/d) which are nearly six times greater than summer thawing rates (1.33–1.36 cm/d). Subsurface dynamics are further regulated by the seasonal snowpack as the shallow winter snow cover (average depth ~ 8.91 cm) is insufficient to form an effective insulating buffer and facilitates the continuous downward propagation of cold energy, while spring snowfall events significantly prolong the spring zero-curtain phase through the mechanisms of meltwater refreezing and latent heat buffering. Thermal orbit analysis supports a seasonal shift in heat transfer modes whereby winter cooling is broadly consistent with conduction-dominated heat propagation, whereas summer dynamics are affected by additional non-conductive and phase-change processes. These findings highlight the role of the coarse-grained active layer as a potential “thermal shield” that may favor the long-term preservation of buried ice. This study provides field-based thermal evidence for the paraglacial transition from glacial to permafrost-dominated conditions and offers essential insights into the hydrological regulation and water storage potential of ice-debris complexes in a warming climate.

Coarse-grained soils are conventionally classified as frost-non-susceptible, yet field evidence revealed significant frost heave in coarse-grained subgrades subjected to confined water, challenging the traditional gradation-based frost susceptibility assessments. To explore the frost heave susceptibility of coarse-grained soil under confined water conditions, four sandy soils containing 0, 5, 10, and 15% fines were tested under stepwise increasing water pressures of 5, 10 and 20 kPa for 9 days using a freeze-thaw apparatus. The thermal regime, ice growth process, and water content profile in samples was obtained and analyzed. Experimental results show that frost heave increases with water pressure and fine content. Based on pre-melting theory, the mechanism by which confined water aggravates the frost heave was explored. It was clarified that the increased hydraulic gradient in the unfrozen water film accelerates the water migration toward ice lens through the film, hence promoting ice growth, ultimately aggravating frost heave. Finally, the reliability of current standards for evaluating the frost heave susceptibility of coarse-grained soil was assessed, then the reasons for the current frost heave susceptibility method failure was revealed, and finally a statistical model incorporating water pressure and fine content was proposed to improve frost heave susceptibility evaluation method.

Freeze-thaw (F-T) cycles strongly affect the hydro-thermal state and deformation stability of soils along cold-region water diversion routes. However, systematic investigations into the cycle-resolved evolution of contrasting deformation modes among heterogeneous route soils under identical field-informed thermal forcing remain limited. Four representative soils along the Tongtian River to Qaidam Basin water-diversion route were subjected to F-T cycling using a field-temperature-based thermal path. Temperature evolution, water distribution, and axial deformation were monitored, while freezing temperature, unfrozen water content, thermal conductivity, and post-F-T structural-state changes were analyzed. The results show that all samples experienced pronounced freezing under the imposed thermal path, with a confirmed freezing depth of at least 90 mm, corresponding to more than 90% of the sample height. After F-T cycling, the water content at all measured positions was higher than the initial value, and stronger water accumulation occurred in the upper part of the samples, indicating upward water redistribution toward the freezing front. The four soils developed distinct residual deformation modes. B-3 showed the strongest frost-heave-dominated response, with a residual deformation ratio of 16.85%, whereas B-4 exhibited a thaw-settlement-dominated response, with a residual deformation ratio of -0.63%. Residual deformation accumulated nonlinearly with F-T cycles. Post-F-T dry density and void ratio changes further indicated that residual frost-heave accumulation was associated with structural loosening and pore expansion, whereas thaw-settlement-dominated behavior corresponded to densification or contraction. These findings reveal the coupled evolution of thermal, hydraulic, and deformation responses of heterogeneous route soils under realistic F-T conditions, providing a basis for identifying deformation-prone sections and improving hydro-geotechnical management of cold-region water diversion projects.

Warming-induced permafrost degradation is accelerating the development and reactivation of retrogressive thaw slumps (RTSs), yet the weekly-scale timing and thermal-hydrologic conditions of activation remain poorly constrained. We develop and test a weekly thermal-hydrologic activation framework and apply it to two RTSs on the northeastern Qinghai-Tibetan Plateau (QTP) using one year of air temperature, ground surface temperature (GST) and active-layer soil-moisture data. A temperature-based snow-cover proxy and a 30-day snow-memory index are derived from the daily GST-air temperature relationship and used to seasonally adjust thermal thresholds. Three weekly indicators are combined using a two-out-of-three rule with majority voting at sensor and site scales. Thresholds are calibrated by grid search and receiver operating characteristic (ROC)/Youden analysis, and moving-block bootstrap resampling is used to quantify uncertainties in activation timing and classification performance. The framework consistently identifies two seasonal activation windows at both sites: an energy-controlled window in May-June, associated with the first seasonal connection of the active layer and initial headwall softening, and a water-controlled window in August, linked to heavy rainfall, high shallow moisture and deeper thaw near the permafrost table. Engineered road units activate earlier than adjacent natural slopes. The classification shows high sensitivity and area under the curve (AUC) values >0.9, with relatively narrow uncertainty intervals at the weekly scale. The framework captures the dual seasonal activation of RTSs and provides a transferable basis for short-term early warning and infrastructure-related hazard assessment in permafrost regions.

Rivers on the Qinghai-Tibet Plateau (QTP) are likely significant contributors to nitrous oxide (N2O) emissions globally. However, direct measurements remain scarce, leaving the underlying mechanisms of N2O emission poorly understood. This study investigated N2O dynamics in the Xuerong Zangbo River on the QTP by integrating in situ measurements, chemical analysis, molecular techniques, and N-15-pairing experiments. Mean dissolved N2O-N concentration was 0.522 +/- 0.166 mu g L-1 in summer and 0.795 +/- 0.271 mu g L-1 in winter, with emission rates ranging from -62.7 to 86.2 mu g m(-2) h(-1) and from -57.5 to 75.8 mu g m(-2) h(-1). Denitrification was the main contributor to the N2O. Microbial community analysis revealed more intense competitive interactions in summer, which were negatively correlated with N2O concentrations and emission factors (EF5r). This implied that microbial competition may disrupt N2O production. The Structural Equation Model (SEM) indicated that warming could inhibit N2O generation by intensifying competition among microorganisms. Additionally, the synergistic effect of wind speed and flow velocity was an important factor controlling the N2O emission rates. This study revealed the mechanisms underlying N2O production and emission of a Tibetan river, offering new insights into the riverine N2O biogeochemical processes on the QTP.

Rock glaciers are important ice-debris landforms in high-mountain permafrost environments, but the development, knowledge base, and emerging directions of this research field remain insufficiently synthesized. This study retrieved English-language article and article/data paper records from the Science Citation Index Expanded database of the Web of Science Core Collection using the query TS = (“rock glacier*” OR “rock glacier*”). After document-type filtering and manual screening, 1125 valid records published between 1910 and 2025 were analyzed. Descriptive bibliometrics were used to characterize scientific production and collaboration patterns, Reference Publication Year Spectroscopy (RPYS) was used to identify historically influential publication years and foundational references, and keyword co-occurrence networks, thematic mapping, and thematic evolution analysis were used to trace associations among research topics. A Logistic life-cycle model was used only as a diagnostic tool for the current publication stage, not as a deterministic forecast. The results indicate that global rock glacier research remains in an active growth stage, although model-derived saturation values should be interpreted cautiously because bibliometric trajectories are affected by database coverage, indexing practices, research funding, technological change, and policy demand. RPYS shows that the knowledge base evolved from geomorphological description, classification, and genetic debate toward permafrost creep, internal structure, thermo-mechanical response, and hydrological significance. Keyword and thematic analyses show increasing attention to climate change, mountain permafrost, InSAR, ground-penetrating radar, hydrological processes, and multi-source monitoring. Because the dataset is restricted to English-language SCI-Expanded records, the results should be interpreted as a map of indexed international literature rather than a complete inventory of all rock glacier knowledge.

In permafrost regions of the Qinghai-Xizang Plateau, embankments of the Qinghai-Xizang Highway and Qinghai-Xizang Railway experiencing roadside water accumulation exhibit more pronounced engineering deteriorations. A widely accepted view is that the accumulated water adjacent to the embankment possesses substantial thermal energy, which accelerates the degradation-even disappearance-of the underlying permafrost. Moreover, the presence of roadside water keeps the embankment soil in a persistently high-moisture state, thereby making the frozen-soil embankment more susceptible to deformation under traffic loading. However, in the permafrost regions of the Qinghai-Xizang Plateau, deteriorations of embankments affected by roadside water are more commonly manifested as undulating pavement surfaces, and extensive crack networks appear on the embankment crest even where thermosyphons are installed. These manifestations are not fully consistent with the deterioration mechanisms proposed by existing viewpoints. We propose the hypothesis that temperature gradients, formed due to the freezing and thawing processes between the roadside water-affected soil and the roadbed soil, lead to moisture migration under the influence of temperature gradients, resulting in frost heave and thaw settlement in the roadbed soil. To validate this hypothesis, we conducted the following investigations sequentially. Initially, we selected a roadbed with a thermosyphon (TPCT) system, which has a significant cooling effect, as the study object. By analyzing the temperature monitoring data of the roadbed section, the temperature variance was calculated to identify the time nodes where the temperature gradient of the roadbed soil was maximum and minimum. Subsequently, corresponding roadbed temperature distribution maps were drawn, illustrating the changes in the temperature and position of the low-temperature core near the TPCT over time. Furthermore, using small-scale indoor model experiments, we qualitatively concluded that moisture in the soil migrates toward the TPCT due to the temperature gradient. Thereafter, combining borehole water content data and precipitation data from the sloped terrain construction site, the formation mechanisms and timing characteristics of roadside water accumulation were analyzed. Ultimately, by integrating the ground temperature data, air temperature data, roadside water formation mechanisms, and the operating characteristics of the TPCT, it was concluded that roadside water, while in a thawed state during TPCT operation, acts as a supplementary source for moisture migration in the roadbed soil. This migration leads to cracking in the TPCT roadbed. Therefore, this study reveals a novel damage mechanism: asynchronous freeze-thaw processes induce temperature gradients, which drive the migration of roadside water into the roadbed and are responsible for the cracking damage.

During the construction of subgrade, the remolding water content w of lime–sand-stabilized clay usually varies in a wide range, leading to inconsistent effectiveness in strength enhancement. Until now, this aspect has not been investigated. In this study, an unconfined compression test and microscopic observation were carried out on clay and stabilized clay (adding 4% lime by mass and 50% sand by volume). The results show the following: (1) remolding water content w had a strong effect on the soil fabrics of pure clay and lime-stabilized clay. An increase in the w from the dry to wet side of optimum reduced matric suction, which diminished the aggregation effect among fine-grained particles in both clay and lime-stabilized clay. Correspondingly, fine-grained aggregate progressively disintegrated, and dispersed fine-grained particles increased. As a result, the w increment at w ≤ wcha made the dispersed fine-grained particles successively fill the large pores between aggregates, densifying the soil fabric. In contrast, at w > wcha, the ongoing disintegration of aggregate resulted in progressive structural weakening. Herein, wcha was defined as the characteristic water content at which the soil fabric transitioned from structural densification to weakening. (2) The UCS of both pure clay and lime–sand-stabilized clay followed a bell-shaped pattern as the w increased, with wcha acting as the turning point. For pure clay soils, the UCS increased with increasing w up to wcha because of structural densification, but decreased beyond wcha due to structural weakening. In lime–sand-stabilized clay, where a sand grain skeleton developed, the compression of lime-stabilized clay induced by the movement of sand grains during shearing activated its contribution to the overall strength. The compressive capacity of the lime-stabilized clay varied in a bell-shaped manner with w, and this trend was mirrored in the UCS of lime–sand-stabilized clay. (3) At a low w, the fact that the clay aggregate exhibited sand-like mechanical behavior reduced the effectiveness of incorporating sand and lime for enhancing the UCS. As the w increased at w ≤ wcha, the breakdown of aggregates enlarged the distinction between pure clay and sand, resulting in a more pronounced improvement in the UCS with the addition of sand and lime. At w > wcha, the lubrication effect occurring at the contact between sand grains diminished the interlocking between the sand grains. Consequently, the effectiveness of the UCS enhancement decreased.

Engineering geological investigations indicate that confined water exists in the stratum during the warm season in permafrost regions and in underground engineering employing artificial ground freezing (AGF) to isolate groundwater, causing significant upward deformation of the stratum and frost damage to engineering structures. However, limited studies have explored the effect and mechanism of hydraulic pressure on ice growth during soil freezing upwards. Therefore, this study designs and conducts four groups of bottom-up freezing tests under various hydraulic pressures, and develops a model to investigate the mechanism of hydraulic pressure on ice growth, based on the theory that liquid water migrates towards the ice lens through an unfrozen water film. The experimental results, including thermal regime, frost heave, cryo-structure, and water redistribution are analyzed systematically, which show the frozen depth, frost heave increment, ice lens thickness, and the layered water content in the samples all increase with hydraulic pressure. The model is validated with experimental data, and the calculation results demonstrate that the ice growth rate increases with hydraulic pressure due to a higher pore water pressure (PWP) gradient in the unfrozen water film. Thus, the characteristics and mechanisms of ice growth in the stratum, accelerated by hydraulic pressure, are clarified. Finally, the applications and implications of this study to engineering geology are discussed, which contribute to a better understanding of ground ice formation in permafrost regions and frost damage prevention in underground engineering performing AGF.

Adsorption is a key mechanism governing water vapor diffusion in lunar regolith. To investigate this process, we conducted experiments under simulated lunar conditions—Knudsen diffusion conditions—using three soil types with varying water vapor adsorption heats and specific surface areas. Results show that soils with higher adsorption heat and larger surface area captured more water vapor. Lower temperatures enhanced water retention across all soil types. In samples with underlying ice, upward migration of water vapor was hindered by adsorption onto soil particles, reducing water loss. Montmorillonite, with its superior adsorption properties, retained the most water under all test conditions. These findings suggest that cold lunar regoliths with high adsorption capacity may act as a favorable reservoir for water accumulation.