Formation and evolution of suprapermafrost taliks beneath earth-filled embankments along the Qinghai-Tibet Railway in permafrost regions

Abstract Taliks are bodies or layers of unfrozen ground in permafrost areas. Suprapermafrost taliks (SPTs) formed between the active layer and permafrost table beneath embankments along the Qinghai-Tibet Railway (QTR) would reduce the stability of the embankments and thus threaten the safety of QTR operations, because the SPTs exhibit a lower bearing capacity than that of frozen ground. This study investigated the formation and evolution of SPTs beneath earth-filled embankments at two monitoring sites (P7 and P17) along the QTR in order to determine the SPTs formation mechanism. The SPTs under the left shoulder of the embankments at P7 and P17 were caused by thermal disturbance of filling and vertical heat accumulation, respectively. The mechanism of SPTs formation beneath the embankments was closely associated with the mean annual ground temperature and the height of embankment filling materials. The study findings can facilitate understanding the formation and evolution of SPTs beneath the embankments in similar sections along the QTR. In particular, the findings can serve as a guidance for the QTR administration bureau in implementing countermeasures for eliminating these unfrozen layers and increasing ground bearing capacity.