Thermal regime simulation of embankment and berm in permafrost

Abstract

During the construction of the Qinghai-Tibet railway (QTR), a testing embankment with berms was built in the Qingshuihe district, Qingzang Plateau, to investigate the effectiveness of berms for permafrost protection. Based on the in situ monitoring data and properties of the fill and foundation soil, and by the employment of a rational temperature boundary, a two-dimensional transient finite element model was built. The model was validated by good agreement with the monitored results. The thermal regime of the berm and embankment was analysed and the thermal insolation effect of the berm with different dimensions and different kind of fills were examined with this model. By extrapolation, the long-term performance of berms under global warming is predicted. The work presented in this paper indicates that (1) with the employment of a rational temperature boundary and enthalpy, the model is proved to be of satisfactory precision, and reliable and workable; (2) different berm dimensions and berm fills have little impact on the thermal regime and the stability of embankment; (3) the existence of berms leads to a larger thawing zone on the southern slope, so that a berm is not an efficient means for permafrost protection, (4) the influence of global warming will result in the degradation of the permafrost under the embankment after several decades. If there are no protection measures, damage will take place mainly on the southern slope of the embankment.