Formation mechanism and characteristics of longitudinal cracking on embankment with TPCTs in permafrost regions of the QTP

Owing to high cooling efficiency without external cooling requirement, two-phase closed thermosyphons (TPCTs) play a certain role in maintaining the stability of embankment in permafrost regions of the QTP. However, pavement disease still exists in the embankments with TPCTs along the Qinghai-Tibet Highway (QTH). We aimed to summarize the type, position and characteristics of pavement disease, and determine the cause, emergence time, and spatiotemporal evolution of longitudinal cracking. This paper involves an on-site investigation, geological radar detection and multi-physics coupling numerical simulation on the pavement disease of embankments with TPCTs along the QTH. The results show that differential settlement and longitudinal cracking are main pavement disease for embankment with vertical TPCTs (VTPCTs), while longitudinal cracking is the main form for embankment with inclined TPCTs (ITPCTs). Longitudinal cracking in embankment with ITPCTs is more developed than the embankment with VTPCTs. Longitudinal cracking at the pavement is attributed to the combination of ground temperature and soil water distributions, and the inflection point for the deformation distribution is the potential position for longitudinal cracking. In embankment with ITPCTs, longitudinal cracking is initiated at the pavement bottom near sunny side center in the 4th service year and propagates at the sunny side. However, in embankment with VTPCTs, longitudinal cracking is initiated at pavement top surface near EC in the 7th service year and propagates at both sunny and shady sides taking EC as the axis of symmetry. This analysis can provide theoretical guidance for the maintenance of the QTH, and the design for the planned Qinghai-Tibet Expressway.