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.

Snow cover and seasonally frozen ground (SFG) are the key cryospheric elements on the southern edge of Altai Mountains (SEAM). Quantifying the thermal effect of snow cover on the frozen ground remains challenging. Utilizing the datasets observed at Altai Kuwei Snow Station (AKSS) and by National Meteorological Stations of China Meteorological Administration (CMA), we evaluated the thermal effect of snow cover on SFG regime. The results observed by AKSS indicated that the energy exchange between the ground and atmosphere was significantly insulated by snow cover, resulting in a considerable temperature offset between the snow surface and the ground below. This offset reached a maximum of 12.8 degrees C for a snow depth of 50 cm, but decreased for snowpack depths of >70 cm, whereas the snow temperature lapse rate was systematically steeper in the upper snowpack than at depth. Snow cover was the dominating driver of inter-annual differences in the SFG regime, as represented by the annual maximum freezing depth and soil heat flux. The observed average soil heat loss rate increased from 2.68 to 5.86 W/m(2) on two occasions when the average snow depth decreased from 61.2 cm to 13.7 cm, resulting in an increase in maximum freezing depth of SFG from 69 cm to >250 cm soil depth. The results observed by CMA also demonstrate how snow cover controlled the SFG regime by warming the ground and inhibiting freezing of the soil column. Snow cover caused a 44.5-cm decline of annual maximum freezing depth during 1961-2015 period. SFG degradation between 1961 and 2015 was accompanied by increases in both air temperature and snow cover, with the former playing the dominant role. The correlation between snow cover and the ground-atmosphere temperature offset provides a new empirical method of evaluating the effective thermal effect of snow cover on SFG.

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.