Laboratory investigation on the pipeline-soil interaction under different freezing conditions

Designing buried natural gas pipelines in frozen ground requires a comprehensive evaluation of the interaction between pipelines and soil, considering the effects of temperature and water supply conditions. One-dimensional freezing experiments are conducted to investigate soil frost heave characteristics and pipelines strain at three cooling modes, namely, constant cooling mode, linear cooling mode, and stepwise cooling mode. The impacts of cooling modes and water supply conditions on freezing rate, frost heave, and pipeline strain are analyzed. The results indicate that the largest soil frost heave occurs at an ambient temperature of -10 degrees C, irrespective of water supply presence. Both the linear and stepwise cooling modes enhance the flatness of the overlying soil, as opposed to the constant cooling mode. The stepwise cooling mode reduces freezing rate, yet leads to a higher tensile strain in the pipeline structure compared to the linear cooling mode. The relative incremental strain is the greatest when the freezing depth ranges from one to two times the diameter of pipelines. The test results could provide a reference for the design of buried natural gas pipelines in cold regions.