Study on the Reasonable Embankment Height of Qinghai—Tibet Railway in Permafrost Regions

Based on the engineering practices of the embankment in permafrost regions of Qinghai—Tibet railway,and starting from the critical height of embankment,which indicates the thermal stability of the roadbed in permafrost regions,we conducted an in-situ experiment along Qinghai—Tibetan railway as well as a series of numerical analysis about the reasonable heights of the railway embankments on the Qinghai—Tibetan Plateau.The in-situ experiment shows that the relationship between the change of man-made upper limit of permafrost soil under the roadbed and the heights of the embankments is non-linear.Whether the height of embankment is either too high or too low,it will cause the decease in the upper limit of permafrost soil under the roadbed.Numerical calculation results show that,under the condition that the mean annual ground temperatures(MAGT) are the same,man-made upper limit of permafrost soil under roadbed will go up with the increase of the embankment height and go down with the increase of roadbed operation time.When the embankment height is higher than certain value,the thawing interlayer will be remained inside the embankment after the first cold season of the embankment completion.The thickness of the thawing interlayer will increase with the increase of the embankment height. Under the condition that the MAGT is-0.3,-0.5,-1.0,-1.5,-2.0 ℃ respectively,the lower limits for the critical heights of the embankments are 6.8,4.2,1.1,0.6,0.5 m,and the upper limits for the critical heights are 3.4,3.4,3.9,4.1,4.4 m.The critical value of MAGT for the existence of a critical height is-0.6 ℃.