In cold regions, the thermal effect of accumulated water on underlying permafrost and permafrost subgrade remains a significant hazard causing engineering risks. Water depth of accumulated water may be an important influence factor of permafrost thermal stability, but there is lack of qualitative and quantitative research about that. In this study, equivalent thermal conductivity theory and solid heat transfer theory have been used to establish the calculation model for simulating heat transfer in water and soil. Thereafter, the accuracy and reliability of the calculation model are checked by monitored data and subsequently used to analyze the thermal erosion of water on underlying permafrost and permafrost under the embankment. These simulation results show that shallow water can protect permafrost and deeper water disrupts the thermal stability of underlying permafrost. The thermal effect extent of water is primarily determined by its depth, and the concept of critical depth and stable depth of accumulated water has been proposed. Moreover, the temperature field of permafrost under embankment can be changed by the slope toe water. In addition, the thermal effect range of the slope toe water is limited by the thermal influence radius, which increases with the depth of standing water. These findings provide support as well as a fundamental base for environmental issues arising from the accumulated water. These observations will, thus, also be valuable to further engineering environment studies in cold regions.

Under the condition of warming and wetting trend on Qinghai-Tibet Plateau due to climate change, summer rainfall infiltration alters the change of the hydrothermal state and may impact the cooling performance of crushed-rock interlayer embankment. Herein, two experimental models with the 1.4-m-thickness (M1) and 0.6m-thickness (M2) crushed-rock layer (CRL) were conducted in an environmental simulator experiencing the freezing and thawing cycles. The hydrothermal response to rainfall events was investigated and quantified by analyzing the variations of measured soil temperatures, volumetric water contents, and heat fluxes. Thermal observations show that rainfall infiltration caused heat advection and resulted in step change of soil temperature at depth. Rainfall infiltration reduced the surface temperature of the CRL, but warmed the soil layer at depth by up to 2.13 degrees C. The average temperature of the base soil layer under the action of concentrated rainfall basically showed an increasing trend. In particular, the CRL with a smaller thickness (M2) had a more significant thermal response to rainfall event. In addition, the moisture pulse, experiencing a step increase and following a gradual decrease caused by rainfall water infiltration, appeared several hours earlier than the temperature pulse. Moreover, infiltrated water produced an additional energy to warm the soil at depth, with maximum heat flux of 12.13 W/m2 and 79.90 W/m2 for the M1 and M2, respectively. The infiltrated water accumulated at the top of base soil significantly delayed the refreezing processes in cold period due to the latent heat effect. The net founding of this study provide an insight into improving the design crushed-rock embankment in permafrost regions.

This article presents the results of field study near a Northern Railway embankment (Hanovey station) in a field work area of the Geocryology Department (Moscow State University), where we performed cone penetration tests, measured the thickness of the active layer and soil temperatures, monitored settlement of the embankment, and performed laboratory tests. A mathematical model was compiled in the Qfrost program based on these data taking the unevenness of the snow cover in the study area into account. Calculations of the temperature regime of the embankment until 2050 taking climate change into account (according to the RCP 4.5 scenario), showed that the thickness of the talik at the embankment will increase by 40% in 30 years and without taking this factor into account, by 17%. This article also discusses the features of the position and structure of the embankment, as well as the composition and properties of frozen soils, which significantly affect the stability of the embankment.

In this article, we consider the problem of thermal response of the near-surface ice-rich permafrost to the effects of linear infrastructure and current climate change. First, we emphasize the scientific and practical significance of the study and briefly describe permafrost conditions and related hazards in the study area. Then we present a mathematical model which accounts for the actual process of soil thawing and freezing and consists of two nonlinear equations: heat conduction and moisture transfer. Numerical calculations were made to predict temperature and moisture conditions in the railroad embankment, taking into account solar radiation, snow cover, rainfall infiltration, and evaporation from the surface. The numerical results indicate that moisture migration and infiltration play the primary role in the development of frost heaving and thaw settlement. During winter, the frost-heave extent is monotonously increased due to pore moisture migration to the freezing front. Strong volume expansion (dilatation) is observed near the surface of the active layer with the onset of the warm season and meltwater infiltration. Settlement of the upper layers of the soil occurs in the summer months (June-August) when there is intense evaporation due to drying. Autumn rains stop the process of thaw settlement by increasing the soil moisture. The above processes are repeated cyclically every year. A frozen core shifts to the shaded side of the embankment under the influence of variations in the solar radiation. Over time, the total moisture content of the frozen core is increased which increases differential heaving and negatively affects the stress-strain state in the embankment. The quantitative and qualitative characteristics of the processes of frost heaving and thaw settlement are obtained in the annual and long-term cycles.

Long-term thermal effects of air convection embankments (ACEs) over 550-km-long permafrost zones along the Qinghai-Tibet railway were analyzed on the basis of 14-year records (2002-2016) of ground temperature. The results showed that, after embankment construction, permafrost tables beneath the ACEs moved upward quickly in the first 3years and then remained stable over the next 10years. The magnitude of this upward movement showed a positive correlation with embankment thickness. Shallow permafrost temperature beneath the ACEs decreased over a 5-year period after embankment construction in cold permafrost zones, but increased sharply concurrent with permafrost table upward movement in warm permafrost zones. Deep permafrost beneath all the ACEs showed a slow warming trend due to climate warming. Overall, the thermal effects of ACEs significantly uplifted underlying permafrost tables after embankment construction and then maintained them well in a warming climate. The different thermal effects of ACEs in cold and warm permafrost zones related to the working principle of the ACEs and natural ground thermal regime in the two zones. (c) 2018 American Society of Civil Engineers.

In this paper, a new method was proposed to decrease the heat accumulation in permafrost embankment by controlling an oriented heat transfer in asphalt pavement Two highly oriented heat-induced structures, named G-OHIS (only gradient thermal conductivity) and G+R-OHIS (combined gradient thermal conductivity and heat reflective layer), were designed by using two indexes of summertime daily heat absorption and annual net heat accumulation on the top of embankment The results showed that the heat absorptions on the top of embankments of the G-OHIS and G+R-OHIS in summer decreased by 9.9% and 23.2% respectively. The annual net heat accumulation on the top of embankment decreased by 6.2% for the G-OHIS and 37.9% for the G+R-OHIS. Moreover, the summertime mean daily temperatures on the top of embankments of the G-OHIS and G+R-OHIS reduced by 0.74 degrees C and 1.66 degrees C respectively. The annual temperature difference on the top of embankment reduced by 1.07 degrees C for the G-OHIS and 1.96 degrees C for the G+R-OHIS. The effectiveness of the G-OHIS in reducing pavement temperature was validated by an indoor irradiation test. It is expected to reduce permafrost thawing and other pavement distresses caused by permafrost thawing by controlling an oriented heat transfer in asphalt pavement. (C) 2016 Elsevier Ltd. All rights reserved.

The G214 expressway is the first major expressway constructed in permafrost regions on the Qinghai-Tibet Plateau. This paper investigates the temperature field distribution and deformation of subgrade by establishing the finite element model. The temperature boundary, vehicle load and the global warming condition of roadbed are considered as influencing factors. The numerical results indicate that subgrade generates large settlement in first year after construction and would reach a stable state in five years. Vertical displacement in embankment internal is related to the variation of melt soil cores. It means that the freeze-thaw cycle makes a big contribution to vertical displacement.