Unfrozen water content of permafrost during thawing by the capacitance technique

Li, Haipeng; Yang, Zhaohui; Wang, Jiahui

doi:10.1016/j.coldregions.2018.04.012

Cited by 31 publications

(11 citation statements)

References 28 publications

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“…Due to the interaction between the coal matrix and its pore space and water, the water in the coal under freezing conditions does not freeze completely, but satisfies a dynamic equilibrium relationship with the temperature; i.e., the unfrozen water content decreases as the freezing temperature of the coal decreases, and there is always some free water present [30,31]. According to the "three zones" theory, the coal can be divided into three zones during freezing [32,33], namely, the unfrozen zone (>0 • C), the freezing zone (0 to −20 • C), and the frozen zone (<−20 • C).…”

Section: Analysis Of the Mechanism Of Water Migration During The Free...mentioning

confidence: 99%

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

Huang

et al. 2021

IJERPH

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This study examines the evolution law of the coal temperature field under low-temperature freezing conditions. The temperature inside coal samples with different water contents was measured in real-time at several measurement points in different locations inside the sample under the condition of low-temperature medium (liquid nitrogen) freezing. The temperature change curve was then used to analyse the laws of temperature propagation and the movement of the freezing front of the coal, which revealed the mechanism of internal water migration in the coal under low-temperature freezing conditions. The results indicate that the greater the water content of the coal sample, the greater the temperature propagation rate. The reasons for this are the phase change of ice and water inside the coal during the freezing process; the increase in the contact area of the ice and coal matrix caused by the volume expansion; and the joint action of the two. The process of the movement of the freezing front is due to the greater adsorption force of the ice lens than that of the coal matrix. Thus, the water molecules adsorbed in the unfrozen area of the coal matrix migrate towards the freezing front and form a new ice lens. Considering the temperature gradient and water content of the coal samples, Darcy’s permeation equation and water migration equation for the inside of the coal under freezing conditions were derived, and the segregation potential and matrix potential were analysed. The obtained theoretical and experimental results were found to be consistent. The higher the water content of the coal samples, the smaller the matrix potential for the hindrance of water migration. Furthermore, the larger the temperature gradient, the larger the segregation potential, and the faster the water migration rate.

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Section: Analysis Of the Mechanism Of Water Migration During The Free...mentioning

confidence: 99%

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

Huang

et al. 2021

IJERPH

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“…The thermal conductivity model derived by Johansen [35] was chosen to determine values of thermal conductivity for both frozen (k f ) and unfrozen soils (k u ). The calculation of k f utilized the unfrozen water content obtained using the capacitance method [36]. For the ground surface layer (gravel fill or organic material), published values of thermal conductivity were used.…”

Section: Thermal Propertiesmentioning

confidence: 99%

Permafrost Thaw and Ground Settlement Considering Long-Term Climate Impact in Northern Alaska

Yang

Lee

2021

Preprint

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Alaska’s North Slope is predicted to experience twice the warming expected globally. When summers are longer and winters are shortened, ground surface conditions in the Arctic are expected to change considerably. This is significant for Arctic Alaska, a region that supports surface infrastructure such as energy extraction and transport assets (pipelines), buildings, roadways, and bridges. Climatic change at the ground surface has been shown to infiltrate soil layers beneath through the harmonic fluctuation of the active layer. Past studies found that warmer air temperature resulted in increasingly deeper thaw, leading to a deeper active layer. This study attempts to assess climate change based on the climate model data from the fifth phase of the Coupled Model Intercomparison Project and its impact on a study site on the North Slope. The predicted air temperature data are analyzed to evaluate how the freezing and thawing indices will change due to climate warming. A thermal model was developed that incorporated a ground surface condition defined by either undisturbed intact tundra or a gravel fill surface and applied climate model predicted air temperatures. Results indicate similar fluctuation in active layer thickness and values that fall within the range of minimum and maximum readings. It is found that the active layer thickens when the ground surface is either gravel fill or undisturbed tundra, but its thickness varies based on climate model predictions. These variations in active layer thickness are then analyzed by considering the near-surface frozen soil ice content. Analysis of results indicates that strain is most significant in the near-surface layers during thaw, indicating that settlement would be concurrent with annual thaw penetration. From this study, the climate model predicted air temperatures for a warming Arctic suggest that the thaw of near-surface frozen ground is largely dependent on ground surface conditions and the thermal properties of soil. Moreover, ice content is a major factor in the settlement predictions on Alaska’s North Slope. This study's results can help enhance the resilience of the existing and future new infrastructure in a changing Arctic environment.

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“…In previous studies, the strength and deformation properties of frozen soil under static conditions considering different influencing factors have been researched. The influence of freezing temperatures ( T ) on the physical and mechanical characteristics of silty clay has been studied by many researchers [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. It has been shown that T could significantly improve the physical and mechanical properties of soils due to the formation of a rigid ice–soil matrix [ 14 ].…”

Section: Introductionmentioning

confidence: 99%

A Nonlinear Constitutive Model for Remoulded Fine-Grained Materials Used under the Qinghai–Tibet Railway Line

et al. 2022

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Using undrained triaxial shear tests, this study investigates the mechanical properties of fine-grained materials (silty clay and sand) which are extensively used for China’s Qinghai–Tibet Railway (QTR) under different confining pressures (σ3) and freezing temperatures (T). The results show that a reduction in T causes an increase in the shear strength and elastic modulus of all the materials tested in the present study. In addition, the freezing of the silty clay has no significant effect on the type of soil behaviour (strain-hardening), whereas the freezing of the sand changes its strain-hardening behaviour to strain-softening. Supposing that the deviatoric stress–strain curves of the silty clay and sand can be divided into two segments due to a reverse bending point, it was assumed that the first segment follows a hyperbolic function. Meanwhile, the second segment is also a hyperbola, with the reverse bending point as the origin and the residual strength as the asymptote. Accordingly, a nonlinear relation constitutive model that considers σ3 and T is derived. All model parameters are identified. The reasonability of the new model was verified using the test results of the materials. A comparison of the predicted and test results shows that this model can well simulate the deviatoric stress–strain response in the failure process of the tested materials. In particular, it can reflect the residual deviatoric stress after the materials’ failure.

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Unfrozen water content of permafrost during thawing by the capacitance technique

Cited by 31 publications

References 28 publications

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

The Temperature Field Evolution and Water Migration Law of Coal under Low-Temperature Freezing Conditions

Permafrost Thaw and Ground Settlement Considering Long-Term Climate Impact in Northern Alaska

A Nonlinear Constitutive Model for Remoulded Fine-Grained Materials Used under the Qinghai–Tibet Railway Line

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