PSI - Issue 30

A.A. Antonov et al. / Procedia Structural Integrity 30 (2020) 11–16 A.A. Antonov et al. / Structural Integrity Procedia 00 (2020) 000–000

15

5

Fig. 4. Section of the I-line of the underwater gas pipeline on Uluu Aryy island, Hatassy village.

When laying the underwater crossings of gas pipelines, the project allows deepening not less than 1 m from natural bottom levels of water bodies and 0.5 m below the calculated deformation of the riverbed during 25 years of gas pipeline operation. State of the line-II of the underwater gas pipeline was inspected as well on the floodplain section of Uluu Aryy island in the area of Hatassy village located on the left bank of the river Lena, 15 km southwards from Yakutsk and 4 km long and on the right bank, on Byldjahyktaah island, which is 2.5 km long. The average burial depth of the underwater gas pipeline in the area of Uluu Aryy island is 1.73 m. The deepest position of the gas pipeline is 3.73 m from the earth’s surface at the intersection of the channel 2911 m far from the reference point. The position of the underwater gas pipeline was measured concerning the checkpoint according to the method of inspecting the planned-high-altitude position. 3. Research results Denudated and sagging sections of the I-line are slightly higher than those of the II-line. Moreover, part of the bare and sagging section of the II-line lies underwater at the minimum depth. The width of the Hatasskaya channel at the time of the inspection of the underwater gas pipeline was ~ 60 m. The visible part of the bare and sagging sections in this area of the route reaches ~ 30 meters. It should also be noted that in the section of the pipeline route adjacent to the left bank, the inverted siphons of the I-st and II-nd lines are elevated in comparison with their location in distant areas. As noted by Permyakov et al. (2011, 2013), such planned-high-altitude position of the inverted siphons of the I and II lines is most likely due to the annual thawing and freezing of soils with their subsequent heaving. In the area of Byldjahyktaah island, the smallest depth of underwater gas pipeline laying is 0.9 m from the earth’s surface and 2489.91 m far from the Hatasskaya channel. A section of the thermokarst appeared in dangerous proximity to the gas pipeline on the right bank with coordinates 61  52 ′ 7.65 ″ C; 129  45 ′ 19.12 ″ B. Its further development may well encompass a section of the gas pipeline route and cause a decrease in the operational reliability of the line-II of the underwater crossing of Hatassy-Pavlovsk MGL across the river Lena. The results of the field surveys of the line-II reveal that the pipe of the underwater gas pipeline runs almost parallel with the surface relief of the area. On the islands from the right bank of the river, there are no wide elevation differences, deep gullies, and channels. Despite this, there is a change in the planned-high-altitude position of the