Permafrost Regions Research Articles

Characteristics of water stable isotopes and runoff sources of a small permafrost basin in northeastern China

Permafrost degradation may have significant impacts on regional water cycles, while little is known about the recharge sources of runoff in permafrost regions, hindering our capability to predict river discharges. Here, a small permafrost basin in Northeast China was selected as the study area. We analyzed isotopic tracers of 186 precipitation, river water, and supra-permafrost water samples collected from May to October 2021. We further calculated the contribution of supra-permafrost water and precipitation to river discharges. The δ18O and δD of precipitation exhibited a significant correlation with air temperature (p<0.05). Similar values and trends were observed in the stable isotope changes of river water and supra-permafrost water, indicating a close hydraulic relationship between the two water sources. Hydrograph separation revealed that supra-permafrost water and precipitation are the first and second end-member of river water in the basin, with a contribution of 85% and 15%, respectively. Overall, our results suggest that supra-permafrost water is the main recharge source of runoff, highlighting the importance of permafrost in the regulation of runoff in small catchments.

Numerical Model of Temperature-Filtration Regime of Earth Dam in Harsh Climatic Conditions

The article addresses the issue of numerical modeling of the process of forming the temperature regime of earth dams, along with their foundations, built and operated in permafrost conditions. A large number of such structures have been constructed in the permafrost regions of the Earth to meet the needs of industry and population. The paper outlines the key principles of designing and constructing such structures. These principles were developed based on years of experience in hydrotechnical construction. Failure to follow these principles leads to structural failures, as confirmed by the presented statistics on accidents. It is essential to ensure the appropriate thermal condition of the structure and its foundation, either frozen or thawed. An unplanned transition of soils from one state to another may lead to an emergency situation. Temperature changes can cause phase transitions of water from liquid to solid (ice), which also affects the formation of the structure’s regime. Numerical methods of calculation allow for the most comprehensive consideration of the influencing factors and processes. The article presents the results of numerical modeling of the filtration-temperature regime of an earth dam with a foundation in permafrost conditions, using two computational programs. The first is based on a locally variational approach (Termic, authored by the researchers), while the second uses a classical linear equation system solution (PLAXIS 2D 2022 software). A comparison of the results obtained from both programs showed good qualitative and quantitative consistency. Under the influence of seepage flow, the zone of frozen ground degradation is spreading in the lower part of the earth dam and its foundation. By September of the 27th year of operation, the thawed ground zone reaches approximately the middle of the structure at the base. The temperature values along the screen axis at the base of the structure are +1.2 °C (according to the Termic program—ver. 1.1) and +1.06 °C (according to PLAXIS 2D PC). Recommendations and future research directions on this topic are also formulated.

Mapping land cover in the low Arctic using multiple sources of earth observation data

Land cover maps in high latitude regions are important for permafrost modeling and mapping and other climate change related studies. National and global land cover products cannot meet the requirements for regional permafrost mapping due to their broad land cover types. This study produced a land cover map in a low Arctic region using multi-source earth observation data, including different modes of RADARSAT-2 (RS2), Sentinel 2 (S2), and the high resolution ArcticDEM. We assessed the performances of two machine learning classification algorithms (Random Forest (RF) and Support Vector Machine (SVM)) with different combinations of input data, including evaluating the effects of incidence angle from different RS2 modes on classification results. This study concludes that the combination of two imaging modes of RS2, S2 composites and the high resolution ArcticDEM achieves a more accurate land cover map (the overall accuracy is 93.6%) than other combinations with the overall accuracies ranging from 38% to 87%; the performance of RF is better than that of SVM, the overall accuracy difference ranges from 21% to 1%; and the shallow SAR incidence angles outperform steep ones in classification results of different combinations for both classifiers.

Land cover change and its driving factors in Siberia from 1992 to 2020.

Siberia occupies vast areas underlain by permafrost, and understanding its land cover changes is important for ecological environmental protection in a warming climate. Based on the land cover and climate datasets, we analyzed the land cover changes and their drivers in Siberia from 1992 to 2020. The results show that ① From 1992 to 2020, the areas of evergreen needleleaf trees and deciduous needleleaf trees in Siberia decreased by 9% and 2.5%, and the areas of grassland, shrub, cropland, and construction land increased by 1.5%, 14.2%, 2.8%, and 39.2%, respectively. Cropland expansion had the fastest rate of 1.85% in the continuous permafrost zone, and construction land expansion had the fastest rate of 3.07% in the non-permafrost zone. ② The center of gravity of agricultural land continues to migrate to the northeast, and the center of gravity of construction land continues to migrate to the southwest. ③ The primary drivers for the land cover changes were temperature and precipitation, and active layer thickness also affected grassland, cropland, and deciduous needleleaf trees. The correlation coefficient between active layer thickness and cropland area is 0.74 in the continuous permafrost zone. The interaction between factors is mostly manifested as a two-factor enhancement, with the highest q-value of the interaction of temperature and precipitation for explanatory power. Our results suggest that climate change and permafrost degradation significantly changed land cover in Siberia. This finding deepens our understanding of the mechanisms of land cover change under the influence of permafrost degradation and provides a new perspective on the land cover changes in permafrost regions.

Study on Soil Freeze–Thaw and Surface Deformation Patterns in the Qilian Mountains Alpine Permafrost Region Using SBAS-InSAR Technique

The Qilian Mountains, located on the northeastern edge of the Qinghai–Tibet Plateau, are characterized by unique high-altitude and cold-climate terrain, where permafrost and seasonally frozen ground are extensively distributed. In recent years, with global warming and increasing precipitation on the Qinghai–Tibet Plateau, permafrost degradation has become severe, further exacerbating the fragility of the ecological environment. Therefore, timely research on surface deformation and the freeze–thaw patterns of alpine permafrost in the Qilian Mountains is imperative. This study employs Sentinel-1A SAR data and the SBAS-InSAR technique to monitor surface deformation in the alpine permafrost regions of the Qilian Mountains from 2017 to 2023. A method for spatiotemporal interpolation of ascending and descending orbit results is proposed to calculate two-dimensional surface deformation fields further. Moreover, by constructing a dynamic periodic deformation model, the study more accurately summarizes the regular changes in permafrost freeze–thaw and the trends in seasonal deformation amplitudes. The results indicate that the surface deformation time series in both vertical and east–west directions obtained using this method show significant improvements in accuracy over the initial data, allowing for a more precise reflection of the dynamic processes of surface deformation in the study area. Subsidence is predominant in permafrost areas, while uplift mainly occurs in seasonally frozen ground areas near lakes and streams. The average vertical deformation rate is 1.56 mm/a, with seasonal amplitudes reaching 35 mm. Topographical (elevation; slope gradient; aspect) and climatic factors (temperature; soil moisture; precipitation) play key roles in deformation patterns. The deformation of permafrost follows five distinct phases: summer thawing; warm-season stability; frost heave; winter cooling; and spring thawing. This study enhances our understanding of permafrost deformation characteristics in high-latitude and high-altitude regions, providing a reference for preventing geological disasters in the Qinghai–Tibet Plateau area and offering theoretical guidance for regional ecological environmental protection and infrastructure safety.

Direct shooting method-based optimized design of novel bridge-like pavement structures

Abstract To mitigate the impact of subgrade settlement on pavement in permafrost regions, an innovative prefabricated pavement structure system composed of longitudinal and transverse beams combined with concrete slabs was proposed and designed. The mechanical performance indicators under the most unfavorable conditions were evaluated using ANSYS finite element software. The direct shooting method was employed to systematically optimize the dimensions of the prefabricated pavement structure components. The results indicate that the prefabricated pavement structure exhibits excellent deformation resistance during subgrade settlement. The direct shooting method optimized the prefabricated pavement structure, ensuring structural safety while reducing weight and minimizing construction costs. Furthermore, a correlation analysis was conducted on the dimensions of the structural components affecting maximum deformation, maximum equivalent stress, and overall structural volume. The analysis identified the significant influence of the upper flange plate of the steel beam and the bottom steel plate on the overall mechanical performance and steel consumption of the pavement structure.

Relationship between soil structure and hydrological properties of the active layer in the permafrost region of the Qinghai–Tibet Plateau based on fractal theory

Soil structure and hydrological properties influence ecosystem stability and hydrological cycles. Fractal theory has been widely used in the quantitative analysis of soil particle-size distribution (PSD), aggregate and pore distribution, and evaluation of soil degradation, desertification, and wind erosion. However, the complex relationships between soil physiochemical properties and soil hydrological processes based on fractal theory have not been thoroughly investigated. This study focused on the correlation among soil structure, physicochemical properties, and hydrological properties in the active layers of various soil types and vegetation coverages in the permafrost region of the Qinghai–Tibet Plateau (QTP) using the principles of fractal theory. The results showed that the fractal dimension of soil PSD (DPSD) in the active layer of the QTP was predominantly within the range of 2.13–2.70, which is notably smaller than the fractal dimension of the soil water retention curve (DWRC: 2.72–2.93). With decreased vegetation coverage, the alpine soil particles exhibit gradual fineness, increasing the DPSD. Soil physicochemical properties were affected by the interactions among internal factors and the external environment, such as geographical locations, slope orientations, vegetation coverages, and soil freeze–thaw cycles. The results of correlation analysis indicated that the fractal dimension of PSD and the soil water retention curve (WRC) were significantly correlated with soil textural, physicochemical, and hydraulic properties, particularly in clay, silt, and very fine sand content. Finally, a fractal model of WRC in the permafrost region was established based on DPSD and WRC parameters of the Gardner and van Genuchten models. The study provides an improved perspective for revealing the transport process and influencing mechanism of soil water and salt in the active layer of the QTP and a more accurate prediction of soil physiochemical and hydrological properties for climate warming and wetting.

Experimental study of polyurethane-cement composite reinforcing talik beneath subgrade in permafrost regions: Exothermic characteristics, durability and micro-mechanism

Experimental study of polyurethane-cement composite reinforcing talik beneath subgrade in permafrost regions: Exothermic characteristics, durability and micro-mechanism

Diversity of primary vegetation species of lake shore impacts largely carbon emissions in thermokarst lakes on the Qinghai-Tibet plateau.

Terrestrial organic matter from surrounding primary vegetation is critical for carbon cycling in thermokarst lakes. However, the characteristics and contribution of this vegetation in shaping microbial community and affecting carbon emissions in thermokarst lakes remain poorly understood. This study quantifies the influence of lakeshore primary vegetation characteristics on microbial community and carbon emissions across lakes with different vegetation types on the Qinghai-Tibet Plateau (QTP). Our findings indicate that methane (CH4) diffusion and ebullition emissions increase significantly from alpine desert (AD), alpine steppe (AS), alpine meadow (AM) to swamp meadow (SM). Specifically, diffusion fluxes in lakes averaged 1.7 mmol m‌‌-2 d-1 (ranging from 0.04 to 5.7 mmol m-2 d-1), and ebullition fluxes in lakes averaged 14.5 mmol m-2 d-1 (ranging from 0.18 to 99.1 mmol m-2 d-1). Carbon dioxide (CO2) diffusive emissions in SM, AM, AS were significantly higher than AD, with fluxes ranging from -14.12 mmol m-2 d-1 to 51.33 mmol m-2 d-1. The primary vegetation diversity also showed a significant increase from AD (3.17 ± 1.33), AS (5.33 ± 1.63), AM (4.5 ± 1.05) to SM (9.2 ± 1.40). Lake shore primary vegetation diversity indirectly enhances CH4 and CO2 emissions by altering water pH. Additionally, it influences methane-cycling microorganisms through pH regulation, further promoting CH4 emissions. Greater vegetation diversity also increases CH4 emissions by affecting sediment microbial carbon. These results underscore the importance of integrating vegetation diversity and microbial community patterns into carbon cycling models to improve the predictions of thermokarst lake carbon emissions in a warming and greening future, emphasizing the urgent requirement to protect the pristine environments of permafrost regions.

Water and carbon fluxes from a supra-permafrost aquifer to a stream across hydrologic states

Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predict the long-term fate of recently thawed carbon in permafrost environments. Here, we used distributed Darcy’s Law calculations to quantify groundwater and DOC fluxes into Imnavait Creek, Alaska, a representative headwater stream in a continuous permafrost watershed. We developed a statistical ensemble approach to model the parameter variability and range of potential contributions of steady-state groundwater flow to the creek. We quantified the model prediction uncertainty using statistical sampling of in-situ, active-layer soil hydro-stratigraphy (water table, ice table, and soil stratigraphy), high-resolution topography data, and DOC data. Moreover, the predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season were also considered given the potential variability in saturation. The model predictions were similar to and span most of the observed range of Imnavait Creek streamflow, especially during recession periods, and also during saturation excess overland flow. As the Arctic warms and supra-permafrost aquifers deepen, groundwater flow is expected to increase. This increase is expected to impact stream, river, and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach.

Numerical study on cooling performance of the L-shaped crushed-rock embankment in permafrost regions

In permafrost regions, crushed-rock embankments are favored for their environmental compatibility and thermal efficiency. This study introduces the innovative L-shaped crushed-rock embankment (LCRE), which features a crushed-rock layer exclusively at the base and on the sunny slope, providing a cost-effective alternative to the conventional U-shaped design. Using numerical methods, we assessed the cooling performance of the LCRE compared to other crushed-rock embankments, focusing on the impact of its geometric parameters. The findings indicate that the overall cooling performance of the LCRE is situated between that of the crushed-rock interlayer embankment and the U-shaped crushed-rock embankment, and its ability to mitigate the shady and sunny slope effect is superior to that of the U-shaped crushed-rock embankment. Additionally, our analysis reveals that increasing the horizontal width of the revetment to enhance cooling is not a cost-effective approach. The LCREs is more suitable for higher embankments than U-shaped counterparts. Despite the LCRE's advantageous thermal performance and cost benefits, its asymmetric load distribution could lead to exacerbated differential settlement, highlighting the need for further research. This study offers pivotal insights into the design and development of innovative crushed-rock embankments in permafrost regions.

Experimental assessment of freeze-thaw deterioration in compression-cast fiber-reinforced concrete

An increasing number of critical infrastructures are built in cold and perma-frost regions, resulting in higher susceptibility to damage due to freeze-thaw (F-T) cycles. This paper assesses the mechanical properties and F-T damage evolution of compression-cast fiber-reinforced concrete (CCFRC) through rapid F-T cycling tests. Nine types of fiber-reinforced concrete (FRC) are experimentally investigated through 144 cubic and 39 prismatic specimens. The main parameters considered in the tests include the casting pressure applied during the compression casting procedure (between 0 and 15 MPa), type of the internal added fibers (polypropylene, end-hooked steel, or their combination), fiber content, and number of F-T cycles. The effects of these parameters on the failure modes, strength degradation rates, deterioration evolution, frost resistance durability, microscopic behavior, and F-T resistance of FRC specimens, are examined in detail. The microscopic performance of different specimens is further investigated using the X-ray computed tomography (X-CT), scanning electron microscopy (SEM), and backscattered scanning electron (BSE) tests. Based on the test results, it is shown that: (i) compared with the mass loss rate, the relative dynamic elastic modulus can be a more suitable index to assess the F-T resistance of FRC; (ii) compression casting and addition of fibers can effectively enhance the F-T denudation resistance of CCFRC; (iii) compression casting reduces the compressive and flexural strength degradation rates of CCFRC, but at the expense of more brittle behavior; and (iv) compression casting and use of the mixed polypropylene and end-hooked steel fibers can effectively delay the F-T cycling induced damage, reduce porosity and internal defects, and enhance the micro-structural behavior and F-T resistance of CCFRC. F-T deterioration prediction models are also proposed and shown to provide accurate and effective representation of the behavior of CCFRC materials.

Attributing the Variations in Evapotranspiration and Its Components of Alpine Grasslands Over the Tibetan Plateau

AbstractClarifying the controlling factors of annual variations in evapotranspiration (ET) and its components (transpiration (T) and evaporation (E)) over alpine grasslands of high‐cold regions is vital to understanding the hydrological processes of the terrestrial ecosystem. Therefore, this study investigated the variability of ET and its components over the alpine grasslands of the Tibetan Plateau (TP) and the driving factors underlying these changes during 1961–2013. The results showed that the annual ET over alpine grasslands was 339 mm, of which 59% and 41% were contributed by E and T, respectively. Annual ET, E, and T over the TP grasslands changed insignificantly before 1995, whereas increased dramatically during 1995–2013. Regarding different alpine grassland types, annual ET and its components in seasonal frost regions (SAG) were larger than in permafrost regions (PAG). The increase of ET and its components in PAG was profoundly larger than that in the SAG region during 1995–2013. Water and energy factors controlled the ET of approximately 65% and 31% area of the TP grasslands, respectively. Leaf area index was the major cause of T variability throughout 64% area of TP grasslands, while regions where energy factors were the major force of T change were mainly located in the eastern SAG region. Variability of E on entire TP grasslands (81%) was mainly regulated by available water supply. Our results indicate that as permafrost degradation has the potential to amplify climate warming and precipitation increase, ET over the PAG region was expected to continue increasing faster than the SAG region.

Sensitivity of the impact of aeolian sand cover on permafrost degradation in the Qinghai–Xizang Plateau

Abstract Environmental transformations and intensifying desertification across the Qinghai-Xizang Plateau significantly influence permafrost degradation, heightening risks associated with carbon emissions, thermal hazards, and infrastructural damage. However, the specific response of permafrost to desertification remains insufficiently understood. Here, we employed numerical modelling to examine the sensitivity of the impact of aeolian sand cover (ASC) on permafrost degradation. Our findings reveal that the thickness and moisture content of ASC profoundly affects permafrost degradation. Moreover, permafrost thermal stability and the rate of climatic warming modulate this degradation process. The simulation results identify two critical thickness thresholds for ASC: 20 cm and 80-120 cm. Specifically, dry ASC thinner than 20 cm accelerates permafrost degradation driven by desertification, whereas ASC thicker than 20 cm mitigates this effect. Furthermore, increased moisture in ASC extends the thickness thresholds to 80-120 cm. These results suggest that climatic variations in the Qinghai-Xizang Plateau, particularly transitions towards either warming-drying or warming-wetting, will markedly influence the response of permafrost to desertification. Notably, a warming-drying climate may reduce the potential degradation of permafrost caused by desertification. This study provides a critical reference for understanding the impact of aeolian desertification on permafrost in regions beyond the Qinghai-Xizang Plateau. It holds significant policy implications for environmental conservation and infrastructure development within the plateau.

Soil organic matter interactions along the elevation gradient of the James Ross Island (Antarctica)

Abstract. Around half of the Earth's soil organic carbon (SOC) is presently stored in the Northern Hemisphere permafrost region. In polar permafrost regions, low temperatures particularly inhibit both the production and biodegradation of organic matter. Under such conditions, abiotic factors such as mesoclimate, pedogenic substrate or altitude are thought to be more important for soil development than biological factors. In Antarctica, biological factors are generally underestimated in soil development due to the rare occurrence of higher plants and the short time since deglaciation. In this study, we aim to assess the relationship between SOC and other soil properties related to the pedogenic factors or properties. Nine plots were investigated along the altitudinal gradient from 10 to 320 m in the deglaciated area of James Ross Island (Ulu Peninsula) using a parallel tea-bag decomposition experiment. SOC contents showed a positive correlation with the content of easily extractable glomalin-related soil protein (EE-GRSP; Spearman r=0.733, P=0.031) and the soil buffering capacity (expressed as ΔpH; Spearman r=0.817, P=0.011). The soil-available P was negatively correlated with altitude (Spearman r=-0.711, P=0.032), and the exchangeable Mg was negatively correlated with the rock fragment content (Spearman r=-0.683, P=0.050). No correlation was found between the available mineral nutrients (P, K, Ca and Mg) and SOC or GRSP. This may be a consequence of the inhibition of biologically mediated nutrient cycling in the soil. Therefore, the main factor influencing nutrient availability in these soils does not seem to the biotic environment; rather, the main impact appears to stem from the abiotic environment influencing the mesoclimate (altitude) or the level of weathering (rock content). Incubation in tea bags for 45 d resulted in the consumption and translocation of more labile polyphenolic and water-extractable organic matter, along with changes in the C content (increase of up to +0.53 % or decrease of up to −1.31 % C) and a decrease in the C:N ratio (from 12.5 to 7.1–10.2), probably due to microbial respiration and an increase in the abundance of nitrogen-binding microorganisms. Our findings suggest that one of the main variables influencing the SOC/GRSP content is not the altitude or coarse-fraction content (for which a correlation with SOC/GRSP was not found); rather, we suspect effects from other factors that are difficult to quantify, such as the availability of liquid water.

Rill erosion and controlling factors on highway side-slopes in the permafrost region

Rill erosion and controlling factors on highway side-slopes in the permafrost region

Research on the Geosynthetic-Encased Gravel Pile Composite Highway Foundation in Low-Temperature Stable Permafrost Regions

In low-temperature stable permafrost regions, both active and passive cooling measures are commonly employed to ensure the long-term stability of highway structures. However, despite adopting these measures, various types of structural issues caused by permafrost degradation remain prevalent in high-grade highways. This indicates that in addition to preventing permafrost melting, structural reinforcement of the foundation is still necessary. Based on the analysis of the long-term foundation temperature field and settlement using the finite element method, which was validated through an indoor top-down freeze–thaw cycle test, this paper explores, for the first time, the feasibility of applying geosynthetic-encased gravel pile composite highway foundations—previously commonly used for permafrost destruction—in low-temperature stable permafrost areas where permafrost protection is the primary principle. By analyzing the long-term temperature field, settlement behavior, and pile–soil stress ratios of permafrost foundations influenced by both the highway structure and composite foundation, it was found that when the pile diameter is 0.5 m, pile spacing is 2 m, and pile length is 11 m, the mean monthly ground temperature of the permafrost foundation will not be significantly affected. Therefore, the properly designed geosynthetic-encased gravel pile composite highway foundation can be adopted in low-temperature stable permafrost regions where permafrost protection, rather than destruction, is required.

A quasi‐continuous long‐term (5 Ma) Mid‐European mountain permafrost record based on fluvial magnetic susceptibility and its contribution to the explanation of Plio–Pleistocene glaciations

The low field magnetic susceptibility (χLF) measured in the 1116‐m‐long Dévaványa core (Pannonian Basin) is a quasi‐continuous record of the Plio–Pleistocene Mid‐European mountain permafrost development. The continuity of fluvial conditions is confirmed by seismic data, and the detrital origin of magnetite is indicated by frequency‐dependent susceptibility measurements, scanning electron microscope, and hysteresis investigations. The χLF record is correlated to the δ18O curve (LR04) supported by palaeomagnetic data. The colour of samples documents precession and obliquity cycles in local facies variations, but the χLF indicates the dominance of 100‐ka eccentricity cycles in the linked mountainous permafrost events. Comparison with orbital solutions revealed that the long‐term development of permafrost occurs as a result of amplitude modulation of the 100‐ka eccentricity cycles. Increases in amplitude of the 100‐ka cycles inhibits permafrost development due to shortened winters. Thus, if extremes are present, the permafrost regions are limited or disappear, but if the 100‐ka eccentricity cycles are attenuated, permanent frost can extend into the temperate zone. This amplitude modulation may also be responsible for the early glaciations during the Pliocene, for the intensification of Northern Hemisphere glaciation, foreshadows cooling in the forthcoming 405‐ka term, and allows the change from 41‐ka cycles to 100‐ka ones in the Mid‐Pleistocene Transition to be explained. The 41‐ka cycles are the result of obliquity‐controlled changes close to the polar cycles, while 100‐ka cycles occur when the amplitude attenuation of the 100‐ka eccentricity cycles enables extended glaciations that suppress the regular 41‐ka cycles. Higher mountains in the catchments enable higher resolution of permafrost records documenting even smaller glaciations. However, the similarities in the overall trends in χLF records of catchment areas with 1500‐m difference in their altitude is a potential counter‐argument when considering the role of tectonic elevations in the expansions of mountainous permafrost.

Soil Texture Mapping in the Permafrost Region: A Case Study on the Eastern Qinghai–Tibet Plateau

Soil Texture Mapping in the Permafrost Region: A Case Study on the Eastern Qinghai–Tibet Plateau

An Analysis of Vertical Infiltration Responses in Unsaturated Soil Columns from Permafrost Regions

Rainfall infiltration affects permafrost-related slope stability by changing the pore water pressure in soil. In this study, the infiltration responses under rainfall conditions were elucidated. The instantaneous profile method and filter paper method were used to obtain the soil–water characteristic curve (SWCC) and hydraulic conductivity function (HCF). During the rainfall infiltration test, the vertical patters of volumetric moisture contents, total hydraulic head or suction and wetting front were recorded. Advancing displacement and rate of the wetting front, the cumulative infiltration, the instantaneous infiltration rate, and the average infiltration rate were determined to comprehensively assess the rainfall infiltration process, along with SWCC and HCF. Additionally, the effects of dry density and runoff on the one-dimensional vertical infiltration process of soil columns were evaluated. The results showed that the variation curve of wetting front displacement versus time obeys a power function relationship. In addition, the infiltration rate–time relationship curve and the unsaturated permeability curve could be roughly divided into three stages, and the SWCC and HCF calculated by volumetric moisture content are more sensitive to changes in dry density than to changes in runoff or hydraulic head height.