PSI - Issue 40

Z.G. Kornilova et al. / Procedia Structural Integrity 40 (2022) 245–250

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Z.G. Kornilova at al./ Structural Integrity Procedia 00 (2021) 000 – 000

As Fig. 1 (a) demonstrates, the high-altitude position of the pipeline approximately repeated the outline of the ground surface in October 2016. Six months later, in April 2017, an intense downward deflection (more than one and a half meters) was observed in the frozen ground near the 165 m benchmark (Fig. 1, b). Another six months later, in October 2017, in the thawed ground, that deflection straightened out. However, a deflection of about 2 meters appeared near the 130 m benchmark (Fig. 1, c). After another season, when the ground had been frozen, in April 2018, the deflection also almost straightened. Nevertheless, a deflection of approximately 1 meter appeared near the 185 m benchmark (Fig. 1, d). The change in the high-altitude position of the pipeline at a certain point can reach up to 2 meters during one period of freezing or thawing. It is a significant movement. The resulting stresses are also considerable. As can be noted, the values of pipeline deformations exceed the possible soil shear from frost heaving. The section presented in Fig. 1 can be divided into three parts: the slope from the floodplain side, the bottom of the channel, and the slope from the side of the island. The water saturation of all three parts is at the same level. Frost heaving in these sections should be approximately equal as well. However, the results of heaving are most remarkable on the floodplain slope. The deformations are less distinct at the bottom and on the island slope, reaching several tens of centimeters, thus, at the level of soil shear during frost heaving. It indicates that, in addition to the heaving itself, another factor affects the deformation of the pipe. We assume that it is the pre-stress that occurred in the pipe during its construction. Since the slope on the left side of the channel is steep, the pipe was heavily bent during laying and became straight along the bottom. The stress from frost heaving is added to the pre stress, causing severe deformations. Assessment of the underground piping stresses is crucial for estimating the service life, especially in areas with moistened soil, where significant deformations occur. To implement the method mentioned above, a computer program that calculates the stress-strain state was created. The numerical solution of the differential equation was attained by the difference method. A five-point approximation of the derivatives was applied to obtain the difference scheme. The h2accuracy has been achieved. Fig. 2 presents the solution to the equation of an underground pipeline according to the data obtained in October 2018 by measuring its planned-high-altitude position in the Hatasskaya channel. The solid line shows the obtained solution of the equation. The squares indicate the measured pipeline depths. The dotted line defines the ground line. As can be seen, the result is close to the measured points, which shows the accuracy of the program.

Fig. 2.The solution to the equation of the underground pipeline