Movement Due to Heave and Thaw Settlement of A Full-Scale Test Chilled Gas Pipeline Constructed in Fairbanks Alaska

摘要

In this paper the authors report the heave and thaw settlement properties of a test chilled gas pipeline. A full-scale field experiment of the chilled gas pipeline system was conducted in Fairbanks Alaska from 1999 to 2005. The length of the test pipeline was 105m and the diameter was 0.9m. The circulated chilled air was –10 oC. One-third of the pipeline was buried in permafrost and the rest of it was placed in non-permafrost. At the end of July 2003, circulation of the chilled air ceased, however, monitoring of the thaw settlement properties of the test pipeline continued until the middle of April, 2005. The results obtained include: 1) As the frost-bulb around the pipeline in non-permafrost section formed, the test pipeline in the non-permafrost section moved upward, resulting in bending of the pipeline at the boundary. 2) In summers, overburden frozen ground of the pipeline became thinner due to the development of active layer above. The pipeline buried in permafrost section moved upward abruptly, fracturing the thinning overburden frozen ground. 3) The phenomenon mentioned 2) occurred successive summer, and the pipeline uplift in permafrost section continued in summers. 4) In relation with 1), the upward movement in non-permafrost section was confirmed by frost heaving of the pipe foundation. 5) Settlement of the test pipeline was also confirmed by thaw settlement of the foundation. 6) During the thawing process, the temperature of the thawing frost bulb became 0 oC at first and then thawed rapidly in summer together with the development of active layer. As a result , settlement of the pipeline happened rapidly in summer.