EVALUATION OF THE EFFECTIVENESS OF RING THERMAL INSULATION FOR PROTECTING A PIPELINE FROM THE HEAVING SOIL

Areas with heaving soil are one of the most complex hindrance for the design and construction of underground pipelines. Inhomogeneity of the geological structure of the base leads to irregular uplifts of soil and pipelines. At least these processes reduce the actual service life. In the worst case, frost heave can cause emergency depressurization, oil or oil products spill and natural gas emission 'into the atmosphere. At the present time, a quantitative evaluation of the of frost heaving dynamic and designing of the protection systems has low accuracy that is confirmed by a numerous accidents occurring on the pipelines every year. To investigate the interaction of pipelines with the heaving soil and the engineering protection system the authors have developed and for the first time ever applied in practice a numerical investigation procedure that allows calculating the stressstrain state of a pipeline taking into account the dynamics of heat and mass transfer and stress-strain state of the soil. The results of the article show the boundaries of applicability of ring thermal insulation for the pipeline in concrete geological conditions. Additionally it was found that in the short sections of frost heaving (length about 3 m) additional stresses from bending are 2.2 times more than in long sections (length 20 m and more). Since the exact location of heaving soil boundary is usually unknown, engineering protection must overlay a dangerous area with a significant margin on both sides to exclude unprotected sections up to 3 m in length