Scour Characteristics of the Underwater Crossing of Trunk Gas Pipeline Across the River Lena

The design data of the underwater crossing of the trunk gas pipeline (TGPL), which is an extension of the main gas pipeline of Hatassy GDS-2, for gasification of regions on the eastern side of the river Lena of the Republic of Sakha (Yakutia) are considered. Scours behaviour of the underwater crossing of TGPL across the river Lena is examined taking into account hydromorphological factors. The influence of hydrological and exogenous processes on the state of the underwater passage of Hatassy-Pavlovsk TGPL is shown by the example of the line-II. Changes of the river bottom profiles in the area of TGPL fixed at four discharge section lines, as well as water consumption were analyzed. It is shown that the presence of the underwater gas pipeline significantly affects the nature of the movement of micro- and meso-forms of the river bottom. It has been established that the constantly changing hydrological and hydromorphological processes resulted in sagging of the inverted siphon section in the line-II of the underwater crossing of Hatassy-Pavlovsk TGPL. During the designing and construction of the first line of the underwater gas pipeline across the river Lena, major omissions were committed, the peculiarities of the hydromorphological and hydrologic features of the river bed evolution in the section of the underwater passage of Tabaga-Kangalassy TGPL across the river Lena had not been taken into account. The effects of hydrodynamic and permafrost processes, heaving phenomena on floodplain and shore slope together increase the non-functional loads on the underwater gas pipeline. As a result of these factors, high longitudinal tensile stresses arise, especially in the welded joints of the inverted siphon pipes, and lead to accidents and incidents at the underwater gas pipeline across the river Lena.