Formation mechanism of longitudinal cracks in expressway embankments with inclined thermosyphons in warm and ice-rich permafrost regions

•Longitudinal cracking of an inclined thermosyphon embankment is studied.•Ground temperature, deformation and stress state of embankment are analyzed.•The induced ground temperature field was the primary cause to the crack.•Warm and ice-rich permafrost contributes to the crack appearance and development.•An improved inclined-vertical thermosyphon embankment is proposed. Thermosyphon-induced longitudinal cracks affect the embankment stability in permafrost regions, which is a serious concern for the Chinese Qinghai-Tibet Expressway (QTE) to be constructed in the near future. Here, longitudinal cracking on the experimental inclined thermosyphon embankment of the QTE in warm and ice-rich permafrost regions is investigated. The cooling effect of the inclined thermosyphons is found to be concentrated in the embankment center, with uneven ground-temperature fields causing embankment differential deformation. Tensile stress concentration is induced on the embankment top surface, with longitudinal cracks potentially being initiated at the maximum tensile stress point. The temporal and spatial initiation of longitudinal cracks is determined by both the embankment stress state and the asphalt-pavement splitting strength. According to the computation, longitudinal cracking was initiated before May or in October–December in the second year after construction completion, 1.8–2.8 m from the embankment center on the sunny half of the pavement. Without significant climate warming change, the main longitudinal crack width development continues with decreasing annual increments, approaching a stable state eventually. To overcome this cooling effect problem for the inclined thermosyphon embankment, the structure should be improved to add cold energy and decrease heat absorption under the slopes. The inclined-vertical thermosyphon embankment proposed herein decreases the embankment cracking probability.