Impacts of supra-permafrost water ponding and drainage on a railway embankment in continuous permafrost zone, the interior of the Qinghai-Tibet Plateau

In a permafrost environment, supra-permafrost water is an important local factor affecting the shallow ground thermal regime and also plays a significant role in geotechnical problems. In this study, the impacts of supra-permafrost water ponding and drainage on the thermal regime and settlement characteristics of a railway embankment in continuous permafrost zone, the interior of the Qinghai-Tibet Plateau were investigated using 13-year records (2003–2016) of field measured data. Results showed that, because of the great latent heat of the ponded water alongside the embankment, a zero curtain layer (ZCL) as much as 5.5 m thick developed in and beneath the embankment after embankment construction in 2003. A three-layered thermal regime developed in the embankment and the subgrade. Although crushed rock revetments were installed 5 years after embankment construction, no soil cooling occurred beneath the ZCL and the ZCL remained stable in thickness. Meanwhile, embankment settlement developed quickly and nearly linearly from 2003 to 2012, with a cumulative settlement approaching approximately 160 mm at both the sunny and the shady embankment shoulders. Compression and creep of warm and ice-rich permafrost layer (WIPL) beneath the ZCL are considered as the main contributors to this significant settlement. Following drainage of the ponded water during 2012, the ZCL cooled quickly and completely frozen after two cold seasons. The underlying permafrost table moved upwards into the embankment and the WIPL cooled with time. Embankment settlement also slowed significantly. However, an asymmetrical temperature field developed in the embankment and the subgrade because of the sunny-shady embankment slope effect, leading to differential settlement between the sunny and the shady embankment shoulders.