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The Lanolin 750 kV electrical transmission line traverses more than 102.86 km through seasonally frozen regions, causing many engineering problems for transmission tower foundations. In this work, physical models of reinforced concrete independent foundations in soils with different frost heave grades were used to simulate the frost heaving performance in seasonally frozen alpine regions. The test results were used to evaluate the tangential frost heaving force calculated based on different specifications. The results showed that the tangential frost heaving force and frozen depth increased with the temperature decrease. Moderately frost-susceptible soils also increased the tangential frost heaving force and frozen depth. Based on technical standards, the main differences between the calculated and the test values were the variable load component and effective frozen depth coefficients. Correcting the coefficient values resulted in a closer agreement between the test and the calculation results. [ABSTRACT FROM AUTHOR]

The Lanlin 750-kV electrical transmission line is 162.45 km long and traverses more than 3.27 km in highly frost-susceptible soil in Lintao County, China, possibly inducing several engineering problems related to frozen soil in the transmission tower foundation. To study the frost heave characteristics of a reinforced concrete foundation in a seasonally frozen alpine region, in this study, physical model tests were performed on independent reinforced concrete foundations under highly frost-susceptible soil conditions and verified via numerical simulations. The temperature field evolution, tangential frost heaving force, unfrozen water content, and frost heave of highly frost-susceptible soil in an open water-refill environment and under dead load were investigated. The influences of surface temperature, overburden loads, and the buried depth of the groundwater level on the frost heave, tangential frost heaving force, and vertical displacement of the foundation were considered in the numerical simulations. Results showed that when the soil is close to the surface, the response of the temperature field is fast and the range of temperature variations is wide. The tangential frost heaving force was the largest in the middle and upper areas of the foundation, reaching a maximum value of 2.18 kN; moreover, the frozen depth and frost heave were 210.42 and 7.20 mm, respectively. The variation curves of the unfrozen water content were similar at all depths, and the replenished water content increased linearly with time. The numerical simulation results showed that the surface temperature considerably influences the frost heave deformation of the foundation, the dead load has a substantial restraining effect on the tangential frost heaving force and vertical displacement of the foundation, and the groundwater level influences the frost heaving ratio and the increment rate of frost heaving force. The fitting degree between the experimental and simulation results was good. Finally, measures for controlling frost heave to guide engineering practices were proposed based on the experimental study and numerical calculation. [ABSTRACT FROM AUTHOR]

Featured Application: Potential applications of this work include predicting the stable stress and strain fields and analyzing the influence factors of frost heave force and deformation of soil surfaces after freezing processes. In analyzing frost heave, researchers often simplify the compressive modulus of freezing soil by considering it as a constant or only as a function of temperature. However, it is a critical parameter characterizing the stress–strain behavior of soil and a variable that is influenced by many other parameters. Hence, herein several one-dimensional freezing experiments are conducted on silty clay in an open system subjected to multistage freezing by considering the compressive modulus as a variable. First, freezing soil under multistage freezing is divided into several layers according to the frozen fringe theory. Then, the correlation between the freezing rate and temperature gradient within each freezing soil layer is investigated. Takashi's equation for frost heave analysis is modified to extend its application conditions by replacing its freezing rate term with a temperature gradient term. A mechanical model for the stress–strain behavior of freezing soil under the action of frost heave is derived within the theoretical framework of nonlinear elasticity, in which a method for determining the compressive modulus of freezing soil with temperature gradient, overburden pressure, and cooling temperature variables is proposed. This study further enhances our understanding of the typical mechanical behavior of saturated freezing silty clay under frost heave action. [ABSTRACT FROM AUTHOR]