Field investigation on the spatiotemporal thermal-deformation characteristics of a composite embankment with two-phase closed thermosyphons on a permafrost slope

The degradation of permafrost caused by climate change and engineering disturbance significantly affects infrastructure stability and transportation safety. Two-phase closed thermosyphons (TPCTs) were widely used to tackle external disturbances by cooling the permafrost stratum in permafrost engineering. However, existing research mainly focuses on the thermal performance of TPCTs. To evaluate the spatiotemporal thermal-deformation characteristics of a composite embankment with L-shaped two-phase closed themosyphons (LTPCTs) on a permafrost slope, we built the first spatiotemporal thermal-deformation observation system for a permafrost embankment with LTPCTs and insulation along the Gonghe-Yushu Highway in the Qinghai-Tibet Plateau, as well as a contrast embankment only with insulation (as a control). The observation results during the first five-year service period indicate that: (1) The cooling performance of LTPCT is determined by the air temperature, and the exterior wall temperature at the top of the evaporator section is significantly affected by the surface ground; additionally, its maximum effective cooling scope is no more than 2.0 m; (2) The LTPCTs can effectively cool down the underlying permafrost in the middle of the composite embankment, and reduce the settlement of the centerline after the second service year; (3) The deformation in the middle of the composite embankment is mainly from the layer of −3.5 to −6.0 m under the bottom of the asphalt layer in the first three years; (4) The maximum settlement near the long sunny slope of the composite embankment can reach 4 times of that at the centerline, and the continuously increasing deformation difference along the cross section may cause longitudinal cracks of the embankment, and influence the traffic safety. Therefore, it is believed that the research results can promote acknowledge for the composite embankments with LTPCTs used in a permafrost slope.