Numerical analysis of temperature fields around the buried arctic gas pipe-line in permafrost regions

Based on one planned arctic natural gas pipe-line engineering which will cross continuous, discontinuous, sporadic and non-permafrost areas from north to south, with different pipe-line temperatures set, a thermal model of the interaction between pipe-line and permafrost is established to investigate the influence of pipe-lines on the freezing and thawing of frozen soil around pipe-line and thermal stability of permafrost. The results show that different pipe-line temperatures influence the permafrost table greatly. Especially in discontinuous permafrost areas the permafrost table is influenced in both positive temperature and negative temperature. The warm gas pipe-line of 5 ℃ could decrease the value of permafrost table about 1 to 3 times pipe diameter and aggravate the degradation of permafrost around pipe-line; –1 ℃ and –5 ℃ chilled gas pipe-line can effectively improve the permafrost table and maintain the temperature stability of frozen soil, but the temperature of soils below pipe-line of –5 ℃ decreases obviously, which may lead to frost heave hazards. In terms of thermal stability around pipe-line, it is advised that transporting temperature of –1 ℃ is adopted in continuous permafrost area; in discontinuous permafrost area pipe-line could operate above freezing in the summer months with the station discharge temperature trending the ambient air temperature, but the discharge temperature must be maintained as –1 ℃ throughout the winter months; in seasonal freezing soil area chilled pipe-line may cause frost heave, therefore, pipe-line should run in positive temperature without extra temperature cooling control.