Settlement of embankments in permafrost regions in the Qinghai-Tibet Plateau

Settlement of embankments in permafrost regions results from several simultaneous processes, each with a different mechanism. The first is the well-known process of thaw settlement due to the degradation of permafrost underneath. This has been considered to be the most problematic and has attracted great attention in previous studies. The second process is that of creep. Field observations show that due to the construction of embankments, the temperature in permafrost layers may rise remarkably, forming a large ‘warmer’ frozen layer with a higher tendency to creep. At the same time, creep of unfrozen soils can take place in the active layer in warm seasons under new loading conditions. Third, because freeze-thaw cycling in the active layer can change the soil properties, additional settlement would also take place in the first years. These three processes are interactive, which makes any attempts at calculation very difficult. The article first reviews the basic methodologies and their limitations for settlement estimation. Then, based on the practice in the construction of a highway and a railway on the Qinghai-Tibet Plateau, the possible settlement sources are analysed. In order to investigate the whole settlement comprehensively with clear mechanisms, the concept of an equivalent permafrost table is proposed.