To analyze the thermal effect of the pile foundation of permafrost, a two-dimensional transient finite element model of the thermal fields with phase change were established. The developments of heat influence limit and maximum thawed depth with and without climate warming were predicted and analyzed. Results indicate that (1) the heat influence limit and maximum thaw depth in permafrost regions enlarge with time elapse, while the global climate warming will have a greater influence to full-space pile foundation compared with the cone-cylinder pile foundation; (2) Considering the global climate warming, heat influence limit (Lmax) and maximum thaw depth (Hmax) in 50th year for full-space pile foundation, cone-cylinder pile foundation are 10.1m, 5.2m, 4.1m, 3.7m, respectively; the maximum thaw depth of full-space pile foundation during the operation will have exceeded the depth of structure (2.5m), which might put the structure at risk; (3) the structure of cone-cylinder pile foundation could effectively preserve permafrost and avoid pile foundations failure; (4) the spacing of cone-cylinder pile foundations is reasonable and the interaction of temperature distribution among cone-cylinder pile foundations can be negligible.

The Geermu-Lasa oil pipeline was located in the Qinghai-Tibet Plateau permafrost regions. The building and operating of pipeline will change the temperature field of soil around it, which can lead to changes of frozen soil mechanic properties, and this will induces deformation or even fracture of pipeline. These phenomena will affect the normal transportation of oil. In this paper, temperature field around the pipelines were analyzed due to different pipe diameters and different insulation layer thicknesses in the way of finite element method. The rule of thawing and freezing of soil around the pipeline in an annual cycle was obtained. Artificial permafrost table variations under the pipeline were also obtained due to different operating conditions. For 30cm diameter pipeline with 7cm insulation layer, its artificial permafrost table depth change value is just 0.48m after 30-year running. These analysis results can provide references to the construction of the new Geermu-Lasa oil pipeline.