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Surface water is an important local factor in engineering geological conditions in permafrost regions. In this paper, the impacts of surface water ponding on the long-term thermal and settlement characteristics of an air convection embankment (ACE) were investigated based on 13 years of data records from field observations along the Qinghai-Tibet Railway (QTR). The time series of the ground temperatures and the settlement of two ACEs with and without adjacent surface water ponding were investigated and compared. The results indicated that surface water ponding could significantly affect the thermal performance of the ACE. Without surface water ponding, the ACE showed a satisfactory cooling effect; the underlying permafrost table rose, and the shallow permafrost layer cooled significantly after construction of the embankment. However, with surface water ponding, the great heat capacity and latent heat of the ponded water and related capillary action impeded the thermal interaction between the ACE and the underlying permafrost. Before the drainage of the ponded water, no permafrost cooling occurred beneath the embankment. The settlement of the two ACEs also differed significantly. The creep of the ice-rich permafrost layer immediately beneath the permafrost table was inferred as the main contribution of the settlement. The temperature of the layer was the main factor determining the rate of settlement. The results can help the hydro-thermal analysis of engineering foundations built over permafrost and provide a reference for embankment construction and maintenance in permafrost regions with rich surface water. • Water ponding can exert significant impacts on thermal performances of the ACE. • The ACE without water ponding showed satisfactory cooling on underlying permafrost. • Settlement of the ACE was mainly induced by creep of ice-rich permafrost layer. • Temperature of ice-rich permafrost layer determined settlement rate of the ACE. [ABSTRACT FROM AUTHOR]

The structural functionality of roads and railways in warm permafrost regions is influenced by both physical and mechanical processes at work within the underlying subgrade. This paper uses ten-years worth of monitoring data to examine the thermal regimes and deformation behaviors of three different types of crushed-rock embankments employed in the construction of the Qinghai-Tibet Railway, which is located in a warm permafrost region of the Tibetan Plateau, China. More specifically, the efficiency of U-shaped crushed-rock, crushed-rock revetment, and crushed-rock basement embankments in stabilizing permafrost temperature is evaluated with consideration to the permafrost table, ground temperature, and mean annual ground temperature. Then, deformation laws in the three embankments were analyzed. Finally, deformation characteristics and sources for general subgrade are discussed and summarized on the basis of monitoring data and previous research. Results show the permafrost table of each of the three crushed-rock embankments to be higher than that of the natural ground at all times, and that the underlying permafrost warms with time regardless of the type of embankment employed. The deformation characteristics of general subgrade in permafrost regions are determined to be non-uniform and persistent. Furthermore, U-shaped crushed-rock embankment out-performed both crushed-rock revetment embankment and crushed-rock basement embankment in terms of cooling capacity and ability to weaken the sunny-shady slope effect. These findings stand to provide important guidance for understanding the deformation mechanisms of subgrade in warm permafrost regions, as well as for improving Qinghai-Tibet Railway embankment quality and operational safety. • Ten-years monitoring data was used to analyze cooling effects of three CREs. • It is concluded that UCRE demonstrates a better cooling effect. • Deformation laws and causes for three CREs were analyzed. • Deformation characteristics and sources for general subgrade are summarized. [ABSTRACT FROM AUTHOR]