Numerical calculation for temperature coupled with moisture and stress of soil around buried pipeline in permafrost regions

Key words:  permafrost  buried pipelines  porous medium  temperature coupled with moisture and stress  numerical calculation

Abstract:

Based on the construction characteristics of Sino Russian crude oil pipeline permafrost regions project, a mathematical model of porous medium coupling of moisture heat of the frozen soil was established. The periodic boundary conditions were adopted for obtaining the ambient temperature and SIMPLER method was used for numerical simulation. The relationship between the cyclic swing of the ambient temperature and the rule of soil temperature, moisture field and ice phase change interface movement was obtained since the late April of the first year when the pipeline was put into operation. The frost heave stress with the field of temperature coupled with moisture was analyzed by the software ANSYS. The results show that the soil temperature around the pipeline changes dramatically in a long period due to the periodic fluctuations of earth 's surface temperature. Top down free convection of the moisture contained in the soil is generated along the center line of the pipeline by the effect of temperature difference and gravity. The modality and intensity in the vortex center of the free convection change significantly with the underground soil temperature changing, and water translocation can be easily impacted by the temperature gradient. At the same time, as the rise of the surface temperature, the thawing rate of soil above pipe is slightly larger than that of the pipe. As the melting cycle expands, the soil around pipe impacted by the small stress range is prone to form heterogeneous frost heaving.