Monitoring investigation on thermal stability of air-convection crushed-rock embankment

The cooling effect and thermal stability of air-convection crushed-rock embankment, including crushed-rock revetment embankment (CRRE) and U-shaped crushed-rock embankment (USCRE), were comparatively investigated by analyzing the ground temperature data collected by a long-term monitoring system along the Qinghai–Tibet Railway. The performances of the CRRE and the USCRE were examined by temperature profiles of six monitoring sites located in permafrost regions with different mean annual ground temperatures (MAGTs). The results indicated that the grounds beneath the USCRE experienced better thermal stability than those beneath the CRRE due to enhanced cooling effect over winter time and insulating effect over summer time of the USCRE. The results also indicated that the thermal stabilities of the air-convection crushed-rock embankments varied with MAGT: in regions with lower MAGT, the air-convection crushed-rock embankments generated stronger cooling effects, and the cooling processes of the shallow grounds beneath the embankments were obvious while the deep ground temperatures kept almost constant; whereas in regions with higher MAGT, especially for the CRRE, the permafrost tables under the embankments had been elevated but the deep permafrost experienced considerable warming. In addition, the differences between ground temperatures beneath right and left shoulders of the embankments were obvious at some monitoring sites, and those thermal differences were closely related to the embankment orientation. The factors determining those thermal differences include solar radiation and may also include wind-forced convection within crushed-rock layers.