PDF(6042 KB)
Similarity Criterion Based on the Analytical Solution of Heat Conduction Equation in Frozen Soil
BO Yin, WANG Cong, FENG Yan-fang, ZHANG Bin, ZHANG Ying, GUO Xiao-gang, YAO Jin-song, WEI Lai, CHEN Rong, XU Chen
Journal of Changjiang River Scientific Research Institute ›› 2025, Vol. 42 ›› Issue (5) : 184-191.
PDF(6042 KB)
PDF(6042 KB)
Similarity Criterion Based on the Analytical Solution of Heat Conduction Equation in Frozen Soil
[Objective] The evolution pattern of temperature field in frozen walls serves as a key factor in optimizing design schemes during artificial ground freezing. At present, laboratory model tests are a critical approach for investigating the development of temperature fields. This study aims to propose a method for deriving similarity criteria for temperature field model tests, offering essential theoretical guidance for the design of laboratory experiments. [Methods] First, analytical solutions to one-dimensional heat conduction differential equations, under both constant and nonlinear thermal parameters, were obtained using the method of separation of variables with different boundary conditions. Based on these solutions, similarity transformation techniques were employed to derive similarity criteria for frozen soil model tests, accounting for both heat exchange and non-heat-exchange conditions. Finally, the finite element software ABAQUS was utilized to conduct numerical simulations of the temperature fields for both prototype and model soils under constant and nonlinear thermal conductivity conditions, verifying the accuracy of the derived criteria. [Results] Results indicated that under non-heat-exchange conditions, when the first-type (Dirichlet) and second-type (Neumann) boundary conditions were combined, the time similarity coefficient equaled the square of the geometric similarity coefficient, enabling rapid determination of model test durations once the geometric scaling ratios were predefined. Similarly, under the combination of second-type and third-type (Robin) boundary conditions, the time similarity constant coefficient remained the square of the geometric similarity constant coefficient. This consistency held regardless of whether thermal parameters were constant or nonlinear, meaning that the time similarity coefficient was the square of the heat conduction geometric similarity coefficient. ensuring uniform criteria between prototype and model cases. When heat exchange was considered, the temperature similarity coefficient was no longer constant. In such cases, the test soil must be replaced and the similarity coefficients of thermal properties such as thermal conductivity, specific heat capacity, and density must satisfy specific quantitative relationships with those of the prototype soil. [Conclusion] The simulation results showed that under the corresponding time and geometric scaling conditions derived in this study, the temperature fields of the prototype and model closely matched, further validating the accuracy of the proposed similarity criteria. The similarity criteria derived from analytical solutions to heat conduction equations fully incorporate the effects of heat exchange boundary conditions and provide a fast and accurate method for determining scaling relationships when similarity coefficients for relevant thermophysical parameters are known. These findings are expected to offer a theoretical basis for solving nonlinear heat conduction problems and for guiding the design and execution of frozen soil model tests.
frozen soil / non-linear heat conduction / analytic solution / similarity criterion / model test
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In order to explore the influence of cyclic freezing and thawing on the deformation characteristics of railway subgrade in seasonal frozen soil region, we performed freeze-thaw cycle test and consolidation compression test on the roadbed filling of Lanzhou-Xinjiang Railway as the research object. Through the tests we obtained the regularities of railway subgrade deformation caused by freeze-thaw cycles and compression characteristics. Moreover, we analyzed the influencing factors of compression characteristics by significance test via orthogonal analysis. Results revealed that the frost heave rate and the melting subsidence coefficient both increased in a power function with the increase of the number of freeze-thaw cycles, and both were positively correlated with water content and negatively correlated with compaction degree at the same freeze-thaw cycle. The compressive modulus of subgrade soil increased at first and then stabilized with the proceedings of cyclic freezing and thawing. The compaction degree (B) had the largest influence on compressive modulus, followed by water content (C), freeze-thaw cycle (A), the interaction between B and C, the interaction between A and B, and the interaction between A and C in sequence. We recommend choosing the compression modulus after nine freeze-thaw cycles as the design value of the road strength of Lanzhou-Xinjiang Railway. The research finding is of guiding significance for the prevention and control of frost heaving and subsidence of railway subgrade.
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Thermal conductivity is an important parameter for estimating thermal regime of permafrost in engineering design. Using QL-30 thermophysical instrument made in Anter Corporation in State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, thermal conductivity of undisturbed permafrost taken from Beiluhe site were studied. Experimental studies show that there are distinct difference in thermal conductivity between undisturbed permafrost and frozen soil. Ice content by volume controls the thermal conductivity of shallow permafrost. For the shallow permafrost with same soil texture, same structure and consolidation condition, it is found that its thermal conductivity has negative correlativity with gas content by volume and positive correlativity with volume density, respectively. On the other hand, gas content by volume is a dominant factor that affects the thermal conductivity of deep permafrost and ground ice. Besides, ground ice in the Tibetan Plateau has the thermal conductivity equivalent to that of pure ice, and gas content by volume affects its thermal conductivity. The studies of thermal conductivity of undisturbed permafrost on the Tibetan Plateau will be helpful to the thermal calculation in the permafrost regions of the plateau.
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To address the issue of foundation stability in construction engineering in cold regions, an experimental study was conducted to investigate the physical and mechanical properties of a frost susceptible silty clay in freezing process. Parameters such as the critical water content for frost heaving, frost heave forces, and shear strength of warm frozen soils were determined. The results indicate that frost shrinkage occurs when the water content of soil samples is below the critical water content for frost heaving. This phenomenon is attributed to the combined effect of frost shrinkage of the soil skeleton and phase transformation of pore water. The vertical displacement curves of soil samples exhibit three types with varying water content: frost shrinkage, frost shrinkage followed by rebound, and frost shrinkage followed by frost heave. The curve of frost heave forces can be divided into two stages, namely rapid growth and stable growth, due to the development of the temperature field. The frost heave force increases as the freezing temperature decreases. The increase in temperature gradient within the active zone of freezing soils, based on the theory of segregation potential, is the cause of higher frost heave forces. When compared to soil samples at normal temperature, the cohesion of frozen silty clay at -3℃ increased from 7.34 kPa to 29.56 kPa, and the internal friction angle increased from 6.40° to 9.18°. However, the shear stress curves did not exhibit brittle failure of frozen soils, but rather displayed characteristics of strain hardening.
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