With the global warming, the permafrost on the Qinghai-Tibetan Plateau (QTP) is degrading significantly, which brings potential threats to the major engineering projects built in or on it, e. g., the Qinghai-Tibet Highway, Qinghai-Tibet Railway, and Xinjiang-Tibet Highway. This study uses advanced survey and statistical methods to reveal the spatial distribution characteristics, development patterns, influencing factors, and formation mechanisms of the damages on the pavement induced by permafrost thawing and freeze-thaw cycles to identify their development process, evolution patterns, and different types of underlying permafrost. This will provide suggestions and guidance to the relevant departments in the decision-making, planning, design, and construction and maintenance of the running or future engineering projects on the QTP.

Climate change has a detrimental impact on permafrost soil in cold regions, resulting in the thawing of permafrost and causing instability and security issues in infrastructure, as well as settlement problems in pavement engineering. To address these challenges, concrete pipe pile foundations have emerged as a viable solution for reinforcing the subgrade and mitigating settlement in isolated permafrost areas. However, the effectiveness of these foundations depends greatly on the mechanical properties of the interface between the permafrost soil and the pipe, which are strongly influenced by varying thawing conditions. While previous studies have primarily focused on the interface under frozen conditions, this paper specifically investigates the interface under thawing conditions. In this study, direct shear tests were conducted to examine the damage characteristics and shear mechanical properties of the soil-pile interface with a water content of 26% at temperatures of -3 degrees C, -2 degrees C, -1 degrees C, -0.5 degrees C, and 8 degrees C. The influence of different degrees of melting on the stress-strain characteristics of the soil-pile interface was also analyzed. The findings reveal that as the temperature increases, the shear strength of the interface decreases. The shear stress-displacement curve of the soil-pile interface in the thawing state exhibits a strain-softening trend and can be divided into three stages: the pre-peak shear stress growth stage, the post-peak shear stress steep drop stage, and the post-peak shear stress reconstruction stage. In contrast, the stress curve in the thawed state demonstrates a strain-hardening trend. The study further highlights that violent phase changes in the ice crystal structure have a significant impact on the peak freezing strength and residual freezing strength at the soil-pile interface, with these strengths decreasing as the temperature rises. Additionally, the cohesion and internal friction angle at the soil-pile interface decrease with increasing temperature. It can be concluded that the mechanical strength of the soil-pile interface, crucial for subgrade reinforcement in permafrost areas within transportation engineering, is greatly influenced by temperature-induced changes in the ice crystal structure.

Rising temperatures due to climate change can significantly impact the freeze-thaw condition of airport pavements in cold regions. This case study investigates the implications of warming temperatures on the freeze-thaw penetration and frost heave of pavements in critical airports across Canada. To this end, different methods were used in the quantification process through climate change simulations considering emission scenario RCP8.5 in 20 and 40 year time horizons. The results show that climate change would have different design implications for airport pavements, depending on their location. The predictions suggest a shallower frost penetration depth, and possibly less frost heave, for the airports not underlain by permafrost, while airports over permafrost areas might experience an increase in thickness of the active layer, ranging from 41 to 57 percent, by 2061. Among the different methods used in this study, it was observed that some methods performed better in predicting the frost depth of fine soils, while others worked better in the frost depth prediction of coarse soils. The results indicate the need for more mechanistic models to provide a more realistic prediction of freeze-thaw penetration, as compared to existing empirical models.

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.

This study investigates whether the diurnal temperature cycle affects the geothermal regime on the Qinghai-Tibet Plateau. To separately characterize this effect, the impact of climatic warming on the ground's thermal regime is eliminated by setting the global warming rate to 0 degrees C/year. The diurnal temperature cycle at the natural ground surface is denoted as sinusoidal functions with amplitudes of 0, 5, 8, and 12 degrees C, respectively. A one-dimensional heat conduction model was utilized to compute the geo-temperature under the natural ground surface, eliminating the effect of geometric boundaries, such as the roadway's embankment, on the geothermal regime. The results show that the diurnal temperature cycle does affect the geothermal regime as (1) under the same mean annual ground temperature, the higher diurnal temperature fluctuation amplitude (DTFA) on the ground surface, the thinner the active layer; (2) the higher the DTFA, the colder the underlying soil. An analysis of the heat flow at the ground surface showed that the diurnal temperature cycle resulted in a net negative heat balance at the earth's surface. This heat loss induced by the diurnal temperature cycle cools the underlying soil. The results and analysis suggest that, currently, the documented numerical model which ignores the diurnal temperature cycle overestimates the warming of the underlying soil. This overestimation, if the DTFA at ground surface is 12 degrees C, would be up to 0.4 degrees C. Considering that pavement surface usually undergoes high diurnal temperature cycles, the impact of the DTFA on pavement subgrade's frost conditions and on the pavement deformation is simply discussed. Published by Elsevier B.V.