Estimating the stability of unprotected embankment in warm and ice-rich permafrost region

The purpose of this study is to estimate the stability of unprotected embankment in the warm and ice-rich permafrost (WIRP) region along the Qinghai–Tibet Railway. The estimation was based on field observations of the varying thermal regime under the unprotected embankments and of the ongoing settlement of this type of embankment. The observed data shows that on the one hand, the unprotected embankment could mitigate the frost heave of the subgrade by homogenizing the geothermal gradient and by decreasing the temperature fluctuation of the WIRP layers. On the other hand, leaving the embankment unprotected has led to the warming of the underlying WIRP layer. This layer releases a considerable amount of unfrozen water. However, the released water undergoes untimely drainage, leading to the ongoing settlement of the embankment. To stabilize the settlement, two recommendations are provided. For those existing unprotected embankments, using shading boards to cool down the underlying permafrost is recommended. For the future embankments constructed in WIRP regions, the inset trenches which are drilled perpendicularly to traffic are recommended to aid the drainage of the released water.