Analyses of temperature fields under the embankment with crushed-rock structures along the Qinghai–Tibet Railway

On the basis of in situ temperature monitoring of the embankments with crushed-rock structures (including a crushed-rock embankment, an embankment with crushed-rock slope protection, and a crushed-rock embankment combined with a crushed-rock slope protection) along the Qinghai–Tibet Railway (QTR), eight monitoring profiles were chosen to analyze changes in ground temperatures due to combined impact of embankment and crushed-rock layer. Embankments were constructed in permafrost regions with different ground temperatures (Region I: Tcp ≥ − 0.5 °C; Region II: − 1.0 °C ≤ Tcp < − 0.5 °C; Region III: − 2.0 °C ≤ Tcp < − 1.0 °C; Region IV: Tcp < − 2.0 °C. Where, Tcp is the mean annual ground temperature at the depth of 15 m). After two to three freeze–thaw cycles, the permafrost tables rose by 1.4 m–3.7 m, which showed that the embankments with crushed-rock structures had a positive effect in cooling the roadbed. At the same time, it was observed that the ground temperature below the permafrost table rose gradually in the initial stages of construction, afterwards, this process was restrained by the embankment which the crushed-rock structures. The degree of restraint varied in the different permafrost regions. The cooling effects on the embankments in Region III and IV were stronger than that in Region I and II.