Ice Segregation Research Articles

A systematic investigation of the freezing process of silty clay through unidirectional stepwise freezing method combined with digital imaging processing technology

Soil freezing represents a complex thermo-hydro-mechanical coupling process that encompasses a range of physical and mechanical phenomena, such as heat transfer, moisture migration, cryostructure development, ice lens segregation, frost heave, and consolidation, all of which interact and influence one another throughout the freezing process. This study conducted a unidirectional stepwise freezing test, comprising three distinct freezing stages, to investigate the freezing behavior of Qinghai-Tibet silty clay using digital imaging processing technology (DIPT), which includes an image acquisition system and a digital image processing system. The results demonstrate that the stepwise freezing test provides a more comprehensive insight into the physical and mechanical processes occurring during unidirectional soil freezing. At various stages of freezing, the temperature distribution within the sample achieves a linear stabilization, with the frozen zone exhibiting a slightly larger extent compared to the unfrozen zone. The longitudinal section of the sample developed layered cryogenic cracks, whereas the horizontal section revealed interconnected cryogenic polygonal cracks of varying sizes, which facilitated moisture migration and ice segregation. Furthermore, ice lenses can segregate within a broad temperature range below the soil freezing point in the frozen zone, resulting in frost heave within the frozen zone and consolidation of the unfrozen zone. This study proposes an experimental method to clarify the complex phenomenon and mechanisms of frost heave during soil freezing.

Water accumulation unrelated to ice segregation near the freezing front during soil freezing: Implications for frost heave in high-speed railway embankments and ground ice formation

Investigating water migration in frozen ground is crucial for understanding the hydrothermal dynamics of frozen soil, which is central to frozen soil engineering (e.g., frost heave) and permafrost environments (e.g., ground ice formation). Previous studies have mostly focused on water migration related to ice segregation in frost-susceptible soils, but less on water migration that is independent of ice segregation in non-frost-susceptible soils. Using a novel layer-scanning method based on the nuclear magnetic resonance (NMR) techniques, the water migration dynamic was observed during the freezing of non-frost-susceptible loess under different drainage conditions (with or without water drainage). Results showed an apparent phenomenon of water migration to the freezing front (TFF) (layer L7) (i.e., water accumulation that is independent of ice segregation) occurred in the early freezing stage of non-frost-susceptible soils under no draining water conditions. The traditional water migration mode is related to ice segregation, a new water migration (including upward and downward) mechanism was proposed to reveal this water accumulation unrelated to ice segregation at TFF. The water accumulation at the freezing front is independent of ice segregation, and is attributed to 9% volume expansion due to pore ice formation in the frozen zone, causing water migration downward TFF; while the decrease of the pore volume of the unfrozen zone (being compressed) accounts for the water migration upward TFF. Investigation into whether ice segregation exists and different modes of water migrations (depending on ice segregation or not) will be greatly helpful for exploring the mechanisms of micro frost heave in the high-speed railway embankments and the thick-layered ground ice formation.

A frost heave pressure model for fractured rocks subjected to repeated freeze-thaw deterioration

Rock engineering in the Tibetan Plateau is usually suffered severe freeze-thaw (F-T) deterioration, triggering numerous geotechnical engineering disasters. As the essential triggering factor of F-T damage, the frost heave pressure (FHP) in rocks should be quantitatively described and predicted. In this study, a novel theoretical model is established and validated to estimate the critical entire evolution process of FHP in fractured rocks subjected to repeated F-T deterioration, in which the influence of fracture geometric configuration, rock mechanical properties and F-T conditions are comprehensively considered. Besides, given the obvious five-stage manner of FHP evolution, the combination effect of different dominant mechanisms in different stages is theoretically addressed. During freezing, after a silence stage induced by temperature above freezing point of water, volumetric expansion and frost-heave cracking separately controls the generation and reduction stages of FHP, and the solutions are obtained based on elastic mechanics and Griffith energy balance theory, respectively. During thawing, ice segregation dominates the second-arising stage of FHP that is quantitatively described via segregation potential and water migration velocity, and then the FHP enters the dissipation stage owing to complete melting of fracture ice. In addition, a decay coefficient is introduced to estimate the influence of F-T cycle number on FHP, and a piecewise FHP model is finally constructed for fractured rocks subjected to repeated F-T deterioration. To validate our new model, a total of 12 F-T cycle tests with real-time FHP monitoring are conducted on granite and sandstone specimens considering three typical influencing factors, i.e., fracture width, rock types and freezing temperatures. A rational consistency is identified between the theoretical and testing results in terms of the FHP evolution curves and the peak FHPs in rock fracture, demonstrating the generalizability and robustness of our proposed model.

Frost heave of subgrade soil under complex traffic loads: Test system and experiments

Soil moisture freezing in cold climates leads to frost heave, a phenomenon influenced by soil texture, temperature, moisture levels, and applied loads. This investigation explores frost heave characteristics of subgrade soil under traffic-induced cyclic stresses, including cyclic compressive stress and alternating horizontal cyclic shear stress. A new frost heave test system was developed, featuring advanced temperature control and accurate loading path reproduction. Comprehensive frost heave experiments were performed to examine the frost heave process under various cyclic stress circumstances. Results indicate that cyclic stresses intensify in-situ frost heave of soil, with horizontal cyclic shear stress having a more significant promoting effect than vertical cyclic stress. The combination of vertical cyclic stress and horizontal cyclic shear stress leads to an increase in segregated frost heave. Moreover, vertical cyclic stress amplifies water absorption during soil frost heave. Total vertical deformation encompasses frost deformation in the frozen zone and consolidation in the unfrozen zone. Vertical cyclic stress may inhibit segregated ice lens formation and encourage consolidation in the unfrozen zone, thereby impeding vertical deformation. The simultaneous application of vertical cyclic stress and horizontal cyclic shear stress results in more intense ice segregation and moisture accumulation near the stable frost front.

JWST observations of 13CO2 ice

The structure and composition of simple ices can be severely modified during stellar evolution by protostellar heating. Key to understanding the involved processes are thermal and chemical tracers that can be used to diagnose the history and environment of the ice. The 15.2 µm bending mode of 12CO2 in particular has proven to be a valuable tracer of ice heating events but suffers from grain shape and size effects. A viable alternative tracer is the weaker 13CO2 isotopologue band at 4.39 µm, which has now become accessible at high S/N with the James Webb Space Telescope (JWST). In this study, we present JWST NIRSpec observations of 13CO2 ice in five deeply embedded Class 0 sources that span a wide range in masses and luminosities (0.2–104 L⊙) taken as part of the Investigating Protostellar Accretion Across the Mass Spectrum (IPA) program. The band profiles vary significantly depending on the source, with the most luminous sources showing a distinct narrow peak at 4.38 µm. We first applied a phenomenological approach with which we demonstrate that a minimum of three to four Gaussian profiles are needed to fit the absorption feature of 13CO2. We then combined these findings with laboratory data and show that a 15.2 µm 12CO2 bending-mode-inspired five-component decomposition can be applied to the isotopologue band, with each component representative of CO2 ice in a specific molecular environment. The final solution consists of cold mixtures of CO2 with CH3OH, H2O, and CO as well as segregated heated pure CO2 ice at 80 K. Our results are in agreement with previous studies of the 12CO2 ice band, further confirming that 13CO2 is a useful alternative tracer of protostellar heating and ice composition. We also propose an alternative solution consisting only of heated mixtures of CO2:CH3OH and CO2:H2O ices and warm pure CO2 ice at 80 K (i.e., no cold CO2 ices) for decomposing the ice profiles of HOPS 370 and IRAS 20126, the two most luminous sources in our sample that show strong evidence of ice heating resulting in ice segregation.

Frost heave model and frost heaving force analysis of permafrost tunnel based on segregated ice

Bi-directional freezing occurs when a tunnel portal passes through an active layer in cold region, or when the tunnel passes through permafrost. The surrounding rock of tunnel portal is frozen by air inside of the tunnel and earth surface. The freezing-thawing cycle of permafrost tunnels is frozen by the permafrost and air inside the tunnel. To investigate the frost heave force on the lining of permafrost tunnels, and verify the layered segregation ice in the surrounding rock of these tunnels, a one-dimensional hydrothermal stress model of bi-directional freezing is established, so as to study the evolution law of segregated ice from the surrounding rock in permafrost tunnels based on the theory of hydro-thermal coupling and segregated ice. After that, based on the mechanical theory, a frost-heave elastic mechanical model including secondary lining, freeze–thaw zone, freezing zone and segregated ice is established. The results show that there is layered segregated ice in the surrounding rock after the lining of permafrost tunnel. The annual difference and the annual average temperature have a great influence on the thickness of segregated ice, while the influence of thermal conductivity is relatively small. The thickness of thawing cycle should be less than 5 m, so that the frost heaving force acting on the lining will not be too large. Good water plugging quality can decrease the thickness of segregated ice. The frost-heaving force acting on the lining increases as the thickness of segregated ice increases. When the thickness of segregated ice is 10 cm, the maximum frost heaving force generated on the lining of single-layer segregated ice is 1.39 times that of non-segregated ice. The frost-heaving force caused by the segregated ice should be considered to guarantee the safety of tunnel structure.

Spatiotemporal variations in frost cracking measures in two dimensions: A case study for rock walls in Jotunheimen, southern Norway

The ground thermal regime has a profound impact on geomorphological processes and has been suggested to be particularly important for weathering processes in periglacial environments. Several frost-related damage indices have hitherto been developed to link climate and frost weathering potential in bedrock, although only for individual points or grid cells. Here, we model ground temperature and frost weathering potential in steep rock walls in the Jotunheimen Mountains, southern Norway, along a two-dimensional profile line for the Younger Dryas Stadial-Preboreal transition (c. 11.5 ka), the Holocene Thermal Maximum (c. 7.5 ka), the Little Ice Age (1750), and the 2010s. We use an established heat flow model and frost-cracking index based on the ice segregation theory. A central innovation of our model treatment is the implementation of ensemble simulations using distributions of automatically mapped crack radii in a rock wall, whereas previous frost damage models considered only a single characteristic crack radius. Our results allowed for the identification of sites with enhanced frost weathering. Such sites are typically found between rock walls and retreating glaciers, as well as in areas where snow depth changes abruptly, resulting in large thermal gradients. Hence, frost weathering may be highly active during glacier retreat, enhancing the damage to rock walls during deglaciation by adding to the damage from stress release. The coldest climates of the Younger Dryas Stadial-Preboreal transition and the Little Ice Age were generally most favorable for frost cracking. Such timing compares well with the knowledge about the timing of rockfall accumulations in Norway.

Simulating ice segregation and thaw consolidation in permafrost environments with the CryoGrid community model

Abstract. The ground ice content in cold environments influences the permafrost thermal regime and the thaw trajectories in a warming climate, especially for soils containing excess ice. Despite their importance, the amount and distribution of ground ice are often unknown due to lacking field observations. Hence, modeling the thawing of ice-rich permafrost soils and associated thermokarst is challenging as ground ice content has to be prescribed in the model setup. In this study, we present a model scheme, capable of simulating segregated ice formation during a model spinup together with associated ground heave. It provides the option to add a constant sedimentation rate throughout the simulation. Besides ice segregation, it can represent thaw consolidation processes and ground subsidence under a warming climate. The computation is based on soil mechanical processes, soil hydrology by the Richards equation and soil freezing characteristics. The code is implemented in the CryoGrid community model (version 1.0), a modular land surface model for simulations of the ground thermal regime. The simulation of ice segregation and thaw consolidation with the new model scheme allows us to analyze the evolution of ground ice content in both space and time. To do so, we use climate data from two contrasting permafrost sites to run the simulations. Several influencing factors are identified, which control the formation and thaw of segregated ice. (i) Model results show that high temperature gradients in the soil as well as moist conditions support the formation of segregated ice. (ii) We find that ice segregation increases in fine-grained soils and that especially organic-rich sediments enhance the process. (iii) Applying external loads suppresses ice segregation and speeds up thaw consolidation. (iv) Sedimentation leads to a rise of the ground surface and the formation of an ice-enriched layer whose thickness increases with sedimentation time. We conclude that the new model scheme is a step forward to improve the description of ground ice distributions in permafrost models and can contribute towards the understanding of ice segregation and thaw consolidation in permafrost environments under changing climatic conditions.

Numerical simulation of frost heave of saturated soil considering thermo‐hydro‐mechanical coupling

AbstractFrost heave can lead to both the ground uplifting and frost heave pressure under different circumstances, and cause many engineering problems. To describe the characteristics of frost heave under various thermo‐hydro‐mechanical (THM) coupling conditions and calculate both the frost heave amount and the frost heave pressure, the coupled THM process, as well as the phase change of the pore water, should be considered for freezing soil. In this paper, thermodynamic equilibrium conditions in saturated freezing soil were derived to account for the mechanical effect on the cryogenic suction and unfrozen saturation of pore water during phase transition. Then the governing equations were developed considering the water flow, heat transfer, stress equilibrium, phase change, ice segregation, and their complex interactions. Based on that, a numerical model considering fully THM coupling is presented within the framework of finite element provided by COMSOL. Both frost heave amount tests and frost heave pressure tests were simulated to verify the proposed model. Then the model was applied to subgrades with different types of soil and different boundary conditions, to reveal the characteristics of frost heave amount and frost heave pressure under different conditions, and at the same time to demonstrate the model's applicative prospect.

Experimental investigation of the erodibility of soda saline-alkali soil under freeze-thaw cycle from a microscopic view

Soda saline-alkali soil, dominated by NaHCO3, has complex engineering properties that change with external water, heat, and salt, making it prone to water erosion. By destroying soil microstructure, freeze-thaw (F-T) action can potentially enhance soil erodibility and provide water erosion material. Therefore, this work examined the freeze-thaw erosive properties and microstructural evolution mechanisms of soda saline-alkali soil. Disintegration tests and a series of microscopic tests examined the impacts of freeze-thaw cycles (N = 0, 1, 5, 10, 30, 60) and soluble salt content (η = 0.4 %, 0.8 %, 1.2 %, 1.6 %, 2.0 %) on the soil erodibility index (disintegration rate). The results demonstrated that F-T action continued to weaken the disintegration resistance of the saline soil. Moreover, this trend relatively stabilized after 10 F-T cycles.Soluble salt content had a two-phase impact on the saline soil disintegration. Increased salt content below 0.8 % improved erosion resistance, but salt content above 0.8 % accelerated the soil erosion. According to the Gouy-Chapman diffuse double layer (DDL) theory, the variation in the thickness of DDL induced by higher sodium ion contents and lower sodium ionic valence were deemed as the main causes. When the salt content increased from 0.8 % to 2.0 %, the disintegration rate increased by 49.40–71.43 %. Microscopic results showed that sequential F-T cycles decreased intra-aggregate pores (<4 μm) and increased inter-aggregate pores (>4 μm). This mechanism was attributed to the unfrozen water migration and ice segregation due to the cryo-suction process during the freezing process. Correlation analysis indicated that soil microstructure with a bimodal characteristic dominated the erodibility index. The effect of F-T action on soil erodibility was more significant than the soluble salt content, with both impacted saline soil erodibility by affecting pore distribution characteristics and soil aggregate formation, respectively. These findings may assist soda saline-alkali soil salinity prevention and control of saline soil erosion in seasonally frozen regions globally.

How Ice Particles Increase Mobility of Rock‐Ice Avalanches: Insights From Chute Flows Simulation of Granular Rock‐Ice Mixtures by Discrete Element Method

AbstractRock‐ice avalanches occurring in cold high‐mountain regions often cause catastrophic damages due to their extremely high mobility. Rock and ice have different physical properties, such as particle size, density, friction, etc., leading to the segregation of rock and ice in the mixture and impacting its mobility. However, how ice affects the mobility of rock‐ice avalanches is still poorly understood. A series of numerical experiments were conducted by using the discrete element method to quantify the effect of rock‐ice particle size ratio and ice content on the particle segregation and mobility of their mixtures. Results show that rock‐ice particle size ratio and volumetric ice content determine the spatial distribution of ice, thereafter affecting the mobility of the rock‐ice mixture by controlling the ratio of particle collision stress and coulomb friction stress. In particular, different from conventional understanding, the ice spatial distribution can have a significantly greater influence on the mixture's mobility compared to the volumetric ice content in some scenarios. This study provides insights into the effect of granular ice on the mobility law in the early phase of rock‐ice avalanches and has important implications for their hazard assessment.

Influences Driving and Limiting the Efficacy of Ice Segregation in Alpine Rocks

AbstractRockwall erosion by rockfall is largely controlled by frost weathering in high alpine environments. As alpine rock types are characterized by crack‐dominated porosity and high rock strength, frost cracking observations from low strength and grain supported pore‐space rocks cannot be transferred. Here, we conducted laboratory experiments on Wetterstein limestone samples with different initial crack density and saturation to test their influence on frost cracking efficacy. We exposed rocks to real‐rockwall freezing conditions and monitored acoustic emissions as a proxy for cracking. To differentiate triggers of observed cracking, we modeled ice pressure and thermal stresses. Our results show initial full saturation is not a singular prerequisite for frost cracking. We also observe higher cracking rates in less‐fractured rock. Finally, we find that the temperature threshold for frost cracking in alpine rocks falls below −7°C. Thus, colder, north‐exposed rock faces in the Alps likely experience more frost cracking than southern‐facing counterparts.

Change of pore water near the freezing front during soil freezing: Migration and mechanisms

The formation and growth of segregation ice dominate the frost heave during soil freezing, which is closely related to water migration. To analyze segregation ice during soil freezing for different soils, a freezing-thawing experiment was conducted with Lanzhou loess (LZL) and Qinghai-Tibet Plateau silty clay (QSC) using a novel layered nuclear magnetic resonance approach. During LZL freezing, the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front, but decreased with decreasing temperature in other layers, whereas during the freezing of QSC, the unfrozen water content in different layers (including the freezing front) decreased with decreased temperature. Notably, the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water. In addition to the temperature gradient, the squeezing action during soil freezing was another important factor affecting water migration, especially at the early stage of soil freezing. However, which of the two factors, squeezing action and temperature gradient, was the dominant one causing water migration depended on soil structure. At the early stage of soil freezing, the squeezing action had a significant effect on the water migration of LZL, but no significant effect on that of QSC. Furthermore, water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice. This study provided an improved understanding for ice segregation and water migration during soil freezing.

Impedance Factor of Hydraulic Conductivity for Frozen Soil Based on Ice Segregation Theory and Its Application

AbstractThe necessity and rationality of using an impedance factor in the calculation of hydraulic conductivity of frozen soil has been an ongoing debate. To address this issue, ice segregation theory was used to analyze the physical meaning of the impedance factor. Based on assumptions sourced from segregation theory, experimental evidence regarding the hydraulic conductivity of frozen soil and the Gibbs‐Thompson effect, a relationship between the impedance factor and soil parameters was deduced. The necessity of the impedance factor was discussed under closed unsaturated and open saturated freezing systems. Finally, the derived impedance factor was compared with the current empirical impedance factor. The results showed the following: (a) The impact of the impedance factor on closed unsaturated freezing systems was small. However, an impedance factor was necessary for water migration in freezing systems with a high degree of ice segregation, such as open saturated freezing systems. (b) The derived impedance factor combined with the VG model had good performance for simulating water migration under different freezing conditions. (c) Compared with the empirical impedance factors, the derived impedance factors considered the effect of segregation acceleration caused by the pore expansion, improving the simulation accuracy of water migration at the freezing front. The parameters used to derive the impedance factor were only the initial porosity and the accumulative curve of the particle size grading, which was easily applied and combined with a VG model as a general method for computing the hydraulic conductivity of frozen soil.

Micro–composition evolution of the undisturbed saline soil undergoing different freeze–thaw cycles

The micro–composition of the soil is closely related to its engineering properties. In Northeast China, seasonal freezing and thawing can induce deterioration of the physicomechanical characteristics of saline soil, which can ultimately lead to engineering failures and geological disasters. To investigate the micro composition evolution including the microstructure and grain size distribution of saline soil under the influence of freeze–thaw cycles, mercury intrusion porosimetry (MIP) and laser particle size analysis (LPSA) were used to test undisturbed saline soil specimens undergoing different freeze–thaw cycles. The pore size distribution curves showed a double–peak shape and the grain size distribution curves showed a bidirectional change. Overall, the pores >0.4 μm increased while the pores smaller than 0.4 μm decreased with increasing freeze–thaw cycles. Moreover, the grain size distribution showed a different changing trend at a pore diameter of approximately 10 μm. During the whole freeze–thaw cycle process, the fragmentation of coarse particles (> 10 μm) and the aggregation of fine particles (< 10 μm) were evident, causing the transformation of different pore sizes, and the bidirectional change existed synchronously in the whole process. The freeze–thaw cycles for saline soil caused the lyotropic salt precipitation and dissolution and the ice volumetric expansion and ice segregation to change the grain size distribution leading to the evolution of pore distribution, ultimately changing the soil micro–composition and resulting in the change of macro engineering characteristics. The study is useful for understanding the change in the engineering properties of saline soil under freeze–thaw cycles from a microscale perspective.

Mobilization of water affecting formation and dissociation of hydrate in clay sediment

Under in situ conditions, common occurrences of liquid water within hydrate-bearing reservoirs have been confirmed during recent field studies. However, the potential influences of such dynamic process – migration of liquid water on formation and dissociation of gas hydrate have still never been investigated. By using brown clay as storer of mobile liquid water, in combination of ice segregation, gradient temperature fields and plane observation windows, and in addition to magnified ‘climbing effect’ under gradient temperature fields, these potentials were investigated. Non-occurrence and even dissociation of hydrate within stability region of methane hydrate are identified; and in comparison with generality of P and T, liquid water migration is responsible for such heterogeneities and localities during hydrate formation and dissociation. For the sample with height of 22.5 cm, upper limit of hydrate converging section does not exceed 15.1 cm and the lower one is above 3.4 cm. I.e. hydrate appearance mainly distributes in the middle and lower section of sample with a range of 6.5 ∼ 9.1 cm and the maximum utilization ratio of sample in vertical direction does accordingly not exceed 45 %. Moreover, ‘breathing’ and ‘water ripple’ vibrations along the bottom of solid as-formed hydrate structures are observed, implying a mechanical driving force to suck up liquid water and then convey away to foster hydrate growth elsewhere. A novel layer-by-layer accumulation growth pattern of hydrate is accordingly proposed, providing a new perspective for the future applications and developments relevant to natural gas hydrate, e.g. resource evaluation of hydrate, over-optimistic comments on current hydrate stability, reason of hydrates exploration technology losing its efficacy, plugging mechanism of hydrate inside pipelines, etc.

The effects of late Cenozoic climate change on the global distribution of frost cracking

Abstract. Frost cracking is a dominant mechanical weathering phenomenon facilitating the breakdown of bedrock in periglacial regions. Despite recent advances in understanding frost cracking processes, few studies have addressed how global climate change over the late Cenozoic may have impacted spatial variations in frost cracking intensity. In this study, we estimate global changes in frost cracking intensity (FCI) by segregation ice growth. Existing process-based models of FCI are applied in combination with soil thickness data from the Harmonized World Soil Database. Temporal and spatial variations in FCI are predicted using surface temperature changes obtained from ECHAM5 general circulation model simulations conducted for four different paleoclimate time slices. Time slices considered include pre-industrial (∼ 1850 CE, PI), mid-Holocene (∼ 6 ka, MH), Last Glacial Maximum (∼ 21 ka, LGM), and Pliocene (∼ 3 Ma, PLIO) times. Results indicate for all paleoclimate time slices that frost cracking was most prevalent (relative to PI times) in the middle- to high-latitude regions, as well as high-elevation lower-latitude areas such the Himalayas, Tibet, the European Alps, the Japanese Alps, the US Rocky Mountains, and the Andes Mountains. The smallest deviations in frost cracking (relative to PI conditions) were observed in the MH simulation, which yielded slightly higher FCI values in most of the areas. In contrast, larger deviations were observed in the simulations of the colder climate (LGM) and warmer climate (PLIO). Our results indicate that the impact of climate change on frost cracking was most severe during the PI–LGM period due to higher differences in temperatures and glaciation at higher latitudes. The PLIO results indicate low FCI in the Andes and higher values of FCI in Greenland and Canada due to the diminished extent of glaciation in the warmer PLIO climate.

High‐resolution stable isotopic signals of ground ice indicate freeze–thaw history in permafrost on the northeastern Qinghai–Tibet Plateau

AbstractUnderstanding the mechanism of formation of ground ice and the freeze–thaw history of permafrost is essential when assessing the future of permafrost in a changing climate. High‐resolution ground ice records, integrating stable isotopes (δ18O, d‐excess, and δ13C), hydrochemistry (EC and pH) data, and cryostratigraphy at a depth of 4.8 m from two contrasting permafrost profiles (P‐1, P‐2) in the Source Area of the Yellow River (SAYR) on the northeastern Qinghai–Tibet Plateau (QTP), were investigated. The results suggested significant depth variations in the stable isotopes and hydrochemistry of the ground ice. The near‐surface ground ice (NSGI) and deep‐layer ground ice (DLGI) were characterized in terms of variations in stable isotopes and known modern active layer data. By synthesizing the measured δ18O and the modeled isotopic fractionation processes during freezing, we suggest that both the NSGI and DLGI in P‐1 were mainly formed by the segregation mechanism during permafrost aggradation. The NSGI in P‐2, however, exhibited quick freezing origins compared with the predominant ice segregation processes for the DLGI. By combining the evolution of various stable isotopes and hydrochemistry with 14C age data, four historical freeze–thaw stages were identified. Specifically, one thawing–refreezing stage (2.8–2.2 m), one freezing aggradation stage (2.2–1.6 m), and two permafrost aggradation–degradation cycle stages (4.8–2.8 m; 1.6–0.7 m) were differentiated, which emphasize the importance of climate‐induced freeze–thaw transitions and differing permafrost aggradation processes on ground ice formation and resultant isotope hydrochemical behaviors. This study is the first to use high‐resolution data in ground ice to interpret the freeze–thaw history of permafrost in the SAYR. These findings are important for further understanding of past permafrost evolution and projected future permafrost degradation trends on the QTP, and provide an alternative method to explore permafrost history.

Study on the Influence of Initial Water Content on One-Dimensional Freezing Process of the Qinghai-Tibet Silty Clay by Using Digital Image Technology

The water content of the foundation soil will change dynamically as a result of rainfall, snowfall, and ground surface evaporation, leading to a significant change in frost heave properties of the foundation soil in cold regions. One-dimensional freezing tests of the Qinghai-Tibet silty clay with three different initial water contents in an open system were carried out using CCD image acquisition technology and computed tomography (CT) scanning technology in combination with the traditional soil freeze-thaw test system. The heat conduct process, cryostructure formation, frost heave development, unfrozen zone consolidation, ice segregation, water migration, and redistribution during soil freezing are studied comprehensively. The results show that increasing the sample’s initial water content will lead to the increase of frozen depth, ladder-like cryostructures in vertical sections, more structural polygons in horizontal sections, and also more obvious ice lens segregation, unfrozen zone consolidation, and water migration during the freezing of soil samples.

Optimization of Conditions for Removal Phenolic Compounds from Water by a Graphene Oxide Aerogel

AbstractIn this study, graphene oxide (GO) was prepared from graphite by improved Hummers’ method. Graphene oxide aerogel (GOA) was synthesized via the ice segregation induced self‐assembly method. Various modern analytical methods were utilized to characterize GOA. The results revealed the aerogel structure with a pore size of 100–150 μm, a specific surface area of 515.21 m2/g, and a pore volume of 2.08–2.16 cm3/g. The synthesized GOA was applied as an adsorbent for the removal of phenol (PN) and bisphenol A (BPA) with a maximum adsorption capacity of 117.65 and 70.17 mg/g, respectively. Response surface methodology involving a rotating central composite design was applied to investigate simultaneously the effects of adsorption variables including adsorption time, pH, and initial concentration on the removal efficiency of GOA for PN or BPA. The results showed that the optimal adsorption efficiency for PN was 92.15 % with an adsorption time of 208.52 min, a pH of 6.08, and an initial PN concentration of 30 mg/L. Regarding BPA, the optimal adsorption efficiency was 95.27 % with an adsorption time of 352.79 min, a pH of 4.91, and an initial BPA concentration of 20 mg/L. The adsorption of both PN and BPA onto GOA was appropriate with the Langmuir model, in which the maximum adsorption capacity of GOA for PN and BPA was 117.65 and 70.175 mg/g, respectively. The results confirmed that the adsorption of PN and BPA onto GOA was monolayer adsorption on a homogeneous surface. The adsorption mechanism of GOA for PN or BPA depended mainly on the electrostatic interaction and hydrogen bonding between −OH of PN, BPA, and oxygen‐containing functional groups of GOA. Besides, π‐π interaction between carbon rings of GOA and PN or BPA also contributed to the enhancement of adsorption performance. The results showed that GOA exhibited potential application in the treatment of organic pollutants. Besides, the evaluation of the morphology of the GOA and the simultaneous effects of different factors can contribute to the advancement of graphene‐based materials and the improvement of wastewater treatment.