In-situ monitoring of settlement at different layers under embankments in permafrost regions on the Qinghai–Tibet Plateau

Ground temperature and settlement at different soil layers are monitored at four typical sections of the Qinghai–Tibet Highway (QTH) and one section of a newly built test road (NBTR) in Beilu River basin, for the purpose of extensive investigation on the rather complicated mechanism of embankment settlement owing to several physical and mechanical processes (i.e., settlement sources) taking place in different soil layers in permafrost regions. Combining the ground temperature with borehole drilling exploration, thawing temperatures of the permafrost layers in the five sections are determined, and then characteristics of permafrost degradation are analyzed. Three types of sections are summarized to clarify different settlement sources in different soil layers. On these bases, characteristics of embankment settlement under different geological conditions are analyzed; the influence of the seasonal changes of air temperature on embankment settlement is discussed; since the two sections, one on QTH and the other on NBTR, are both located in Beilu River basin, they are compared with respect to the variation of the main settlement source in the process of permafrost degradation. The results help to understand the mechanism of embankment settlement.