青藏铁路冻土路基合理路堤高度研究

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

从反映冻土路基热稳定性的路堤临界高度出发,结合青藏铁路冻土路基试验工程,对青藏高原冻土路基的合理路堤高度进行现场试验研究及数值模拟研究。现场试验结果表明:路基下冻土人为上限的变化与路堤高度呈非线性关系,路堤高度太小或太大都会造成路基下多年冻土上限的下降。数值计算结果表明:在相同年平均地温条件下,路基下冻土的人为上限随路堤高度的增大而上升,随路基运行时间的增长而下降;当路堤高度大于一定数值时,在路堤建成的第1个寒季过后,路堤内会残留融化夹层,并且融化夹层的厚度随路堤高度的增加而增大;年平均地温分别为-0.3,-0.5,-1.0,-1.5,-2.0℃条件下,路堤的下临界高度分别为6.8,4.2,1.1,0.6,0.5 m;上临界高度分别为3.4,3.4,3.9,4.1,4.4 m。路堤临界高度存在的年平均地温临界值约为-0.6℃。

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 ℃.