Investigating characteristics of the long-term settlement of railway embankments in warm permafrost areas

Abstract

Introduction: The embankment in the permafrost zone of the Qinghai–Tibet Railway (QTR) faces the problem of permafrost degradation, especially in the warm and ice-rich permafrost areas. The settlement deformation of the embankment is more serious in these areas.Methods: This study systematically investigates the settlement deformation characteristics during 16 operational years of three types of typical roadbed structures. The traditional embankment (TE), U-shaped crushed-rock embankment (UCRE), and crushed-rock revetment embankment (CRRE) are the roadbed structures. The long-term monitoring ground temperature and deformation data of the embankment section along the QTR in warm permafrost areas from 2005 to 2020 are utilized in analysis.Results and Discussion: This study focuses on the influence law of the roadbed structure form, shady–sunny slope effect, and temperature field change on the settlement of the roadbed. The results indicated that the two types of the crushed-rock embankment (CRE) of the long-term cumulative settlement are less than 50% of the cumulative settlement of the TE, and the impact on controlling the settlement is significant. The annual settlements of the three types of embankment structures are related to the artificial permafrost table (APT) and influenced by cyclical climate change at the regional scale. The annual growth rate of the settlement at the left and right shoulders of the UCRE as a result of the effect of the shady–sunny slope does not vary considerably as the number of operational years increases. The impact of the shady–sunny slope on the CRRE for the various settlements before 2008 was negligible. After 2008, the thermal disturbance to the embankment temperature field induced by the preconstruction and the effect of shady–sunny slopes decreased gradually as the number of operational years increased. In some years of operation, a thawed interlayer in the TE and CRRE greatly affected the embankment settlement acceleration. The settlement growth rate of the TE is related to the decline of the artificial permafrost table (APT). During the operational years, there was no thawed interlayer in the UCRE. The development of the settlement rate is unaffected by the temperature field for either the left or right embankment shoulder.