Study on settlement of unprotected railway embankment in permafrost

An in situ testing of a selected railway embankment in Qingshuihe region, Tibet Plateau, is described where no artificial protection measure was employed. Based on the results obtained, characteristics of the distribution of geotemperature and settlement of the embankment are examined. An assessment of long-term stability of the embankment is made, and a kind of efficient engineering treatment is recommended in this paper. The study reveals: a) although the permafrost table did not move after embankment construction, the layer between ground surface and the permafrost table approached the phase-transition critical state, i.e. 0.0 °C. This layer is about 3.0 m thick, and is the major source of embankment settlement; b) the varying heat-absorption at different locations along the cross-section of the embankment leads to a differential settlement, and results in the longitudinal cracking; c) the settlement developed at a constant rate (about 0.06 m/year in the middle of the embankment) during the complete test period; d) the optimal railway embankment height differs from that for highways, and should be less. Further study of the optimal height should be carried out comprehensively and the results applied to engineering practice immediately, since this could not only keep the permafrost table stable but also limit the differential settlement to an acceptable level; e) asymmetrical protection measures should be employed to reduce the differential settlement and longitudinal cracking; f) it is most important that embankment construction in permafrost area be carried out during the cold season.