Numerical evaluation for cooling performance of a composite measure on expressway embankment with shady and sunny slopes in permafrost regions

As an efficient engineering measure for protecting permafrost from thawing, the composite measure composed of L-shaped two-phase closed thermosyphons (TPCTs), insulation board and crushed-rock revetments (CRs) is applied to the low-grade highway in the Qinghai-Tibet Plateau. However, it is uncertain whether this composite measure can be available for an expressway embankment with wide bituminous pavement and strict deformation requirement, and the deformation performance of the embankment with composite measure is the key factor controlling safe operation. In this study, a hydro-thermo-mechanical coupled model for the expressway embankment combined with the composite measure is developed, the working process and mechanism of L-shaped TPCTs, insulation board and CRs are analyzed, respectively, and the cooling and reinforcing effects of the composite measure for the embankment with shady and sunny slopes are evaluated. The numerical results show that: (1) The working process and mechanism of L-shaped TPCTs, insulation board and CRs are different. (2) The composite measure can not only prevent the permafrost degradation, but also relieve the asymmetric geotemperature and moisture distributions caused by shady-sunny slope effect. (3) The composite measure can significantly reduce the embankment deformation, reliably alleviate the deformation difference and reinforce the stability of the expressway embankment in permafrost regions.