Abstract
Thawing landslide is a common geological disaster in permafrost regions, which seriously threatens the structural safety of oil and gas pipelines crossing permafrost regions. Most of the analytical methods have been used to calculate the longitudinal stress of buried pipelines. These analytical methods are subjected to slope-thaw slumping load, and the elastic characteristic of the soil in a nonlinear interaction behavior is ignored. Also, these methods have not considered the real boundary at both ends of the slope. This study set out to introduce an improved analytical method to accurately analyze the longitudinal strain characteristics of buried pipelines subjected to slope-thaw slumping load. In this regard, an iterative algorithm was based on an ideal elastoplastic model in the pipeline-soil interaction. Based on field monitoring and previous finite element results, the accuracy of the proposed method was validated. Besides, a parametric analysis was conducted to study the effects of wall thickness, internal pressure, ultimate soil resistance, and slope angle on the maximum longitudinal strain of the pipeline. The results from the compression section showed that the pipeline is more likely to yield, indicating an actual situation in engineering. Moreover, the maximum longitudinal tensile and compression strain of pipelines decrease with increasing the wall thickness, internal pressure, ultimate resistance of soil, and slope angle. Finally, based on the pipeline limit state equations in CSA Z662-2007 and CRES which considered the critical compression factor comprehensively, the critical slumping displacements for both tensile and compressive strain failures were derived for reference. The research results attach great significance to the safety of pipeline under slope.
Highlights
Permafrost regions in China account for 22.4% of the total land area, mainly distributed in the QinghaiTibet Plateau and the Great and Small Xing’an Mountains (Xu et al, 2010)
The purpose of the current study was to introduce an improved analytical method for the longitudinal strain analysis of buried pipelines subjected to the thaw slumping load
A bilinear stress-strain model was adopted to the pipe material, and the pipe-soil interaction was assumed to be an ideal elastoplastic model
Summary
Permafrost regions in China account for 22.4% of the total land area, mainly distributed in the QinghaiTibet Plateau and the Great and Small Xing’an Mountains (Xu et al, 2010). Among the several oil and gas pipelines that have been crossed, e.g., the Gela pipeline unavoidably traverses the permafrost regions. In China, the Mo-Da line is the first long-distance pipeline that passes through the permafrost regions. The length of slopes is mostly over 200 m, and the most extended slope reaches more than 3,000 m. It faces the risk of thawing landslides during pipelines implementation. The stability of slopes is one of the severe problems faced by pipelines in frozen soil areas (Mcroberts and Morgenstern, 1974). Slope-thaw slumping often occurs along with frozen soil melting (FSM). The FSM in the trench attaches complex force loadings to the buried pipelines, which is vulnerable to changes in operating temperature, vegetation damage on the pipeline route, climate warming, and other factors
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