PSI - Issue 65

D.S. Ivanov et al. / Procedia Structural Integrity 65 (2024) 102–108 D.S. Ivanov, G.S. Ammosov, Z.G. Kornilova, A.A. Antonov / Structural Integrity Procedia 00 (2024) 000–000

103

2

1. Introduction

In Yakutia, underground pipelines are laid in permafrost soils. Therefore, the crucial task lies in studying the load from the impact of frost heave. The soil impact on a pipe can be force, heat, moisture, chemical, etc. The pipeline affects the soil by constant loads, such as the weight of the pipe, pressure on the soil, changes in temperature, and pressure of the pumped product. In permafrost areas, the deformations of an underground pipeline are mainly caused by the mechanical movement twice a year due to seasonal freezing and thawing of the foundation soils by Lebedev M.P. et al.(2018). Frost heaving can lead to tight bending of pipelines, sagging of individual sections, displacements, and an increased stress-strain state may occur. Such sections can be predicted by calculation by Burkov P.V. et al (2013), Lisin Yu.V et al (2012). The article presents the results of measurements of the planned-high-altitude positions of the pipeline at the head of the Tabaginskaya anabranch at an interval of six months. Long-term annual monitoring of the underground pipeline has revealed sections where the pipeline, laid in permafrost soil, deforms twice a year in different ways. The changes in the high-altitude position reach up to two meters in six months by Ivanov D.S. et al (2022). Intensive semi-annual deformations of the underground pipeline require a detailed study of the formation mechanisms and assessment of the stresses arising in the pipeline. As shown in Figure 1, the pipeline displacements reach large values over six months, for example, up to two meters on a section of 180-200 meters, and seriously endanger the stable operation. The deflection of a deformed pipeline is determined from the data of the planned-high-altitude measurements, from which the bending radius is calculated, and the resulting stress is assessed by Ainbinder A.B.and Kamershtein A.G. (1982) and Yasin E.M. and Chernikin V.I. (1967). However, in the measured section, the deflections occur without intervals: convexity turns to concavity, which turns into convexity, and so on. Figure 1 shows the measured high-altitude position of the pipeline. The pipeline was initially laid in a straight line. Now, it bends in a series of arches following one another without intervals. We call this type of deformation complex, in contrast to the case when the deformation of the pipeline resembles a single arch. Figure 2 demonstrates the same complex deformation.

Fig. 1. Pipeline deformation in six months: ‒‒‒ ‒ daylight surface of the soil, ‒  ‒ position of the underground pipeline measured in April 2018 (frozen soil), ‒  ‒ ‒ November, 2018. (tabet soil), ----- ‒ interpolated position of the pipeline.

The present paper aims to recover the function of a pipeline’s spatial position from horizontal and vertical point data, obtain the bending radius, and estimate the stresses.