SU1665152A1 - Method for construction of buried pipeline in unstable soil thawing areas - Google Patents

Abstract

The invention relates to construction and can be used in the construction of pipelines in permafrost soils. The purpose of the invention is to increase the operational reliability of the pipeline by limiting the size of the thawing halo. In section 1 of unstable soils, pipeline 2 is branched and laid in several strings 3 - 5 in different trenches. At the boundaries of section 1, shut-off and switching valves 7 are installed. Regulation of the thermal interaction of the pipeline with permafrost soil within section 1 is carried out by alternately switching the pumping of the product along each string 3 - 5 when the maximum permissible thawing halo is reached around it 8. The distance between the threads 3 - 5 is established from the condition of excluding their mutual thermal influence. 3 il.

Description

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The invention relates to construction and can be used in the construction of pipelines in permafrost soils.

The purpose of the invention is to increase the operational reliability of the pipeline by limiting the thawing halo.

FIG. 1 shows a pipeline laid on a section of unstable soils, the super-angle view of FIG. 2 is a section A-A in FIG. one; in fig. 3 is a graph of the growth of thawing halos and sediment depending on the number of switchings of the pipeline threads.

In section 1 of unstable soils, pipeline 2 is branched and laid in several lines 3-5 in different x 6 trenches.

At the same time, on the borders of section 1 with a length equal to the distance I, shut-off and switching valves 7 are installed. Regulation of the thermal interaction of the pipeline 2 with permafrost soil within section 1 is carried out by alternately switching the product over each of the threads 3-5 after reaching the value thawing halo 8 of a predetermined value of N. The acceptable thawing halo 8 is prescribed from the condition of the strength of the pipeline 2 during its precipitation on an unevenly subsiding base. The distance L between threads 3-5 is established on the basis of excluding their thermal influence on each other. The required number of threads 3-5 is determined by the technological parameters of operation and the technical and economic substantiation of the efficiency of using the method. For example, when the defrosting halo reaches 8 H values around line 3, the pumped product is switched to backup thread 4. On line 3, the defrosting halo 8 decreases to position 9. When the thawing halo reaches 8, the value of the predetermined value - N does the switching of the pumped product onto the string 5. In this case, on the string 3, the defrosting halo 8 can be fully restored. Upon reaching the 5 thaw of 8 with a value of H equal to thawing, the transfer is switched to string 3, where thawing of the thawing halo 8 has already occurred. Thus, by alternately pumping the product along each of the threads of pipeline 2, the allowable defrosting halo 8 equal to H is maintained, which eliminates the use of special structural and technological elements at site 1 (heat insulation, cooling installations) and preserves the necessary operational reliability of the pipeline 2

The defrosting of defrosting halos 8 is more intense than defrosting, due to the fact that defrosting is carried out from a point source of heat, while the entire array of permafrost and atmospheric cold from the surface contribute to freezing. When the soils are thawed again (second and subsequent switching), the sediment will increase only due to the thawing of a new zone of frozen soils that had not been thawed before. However, this zone will be insignificant.

FIG. Figure 3 shows the results of calculating the growth of thawing halos and sediment. The graph shows that the largest increase is observed in the first years of operation (1st and 2nd switching), with subsequent switchings this increase is minimal, and by the end of the service life of pipeline 2 (after 20 years), the values of halo thawing around the threads 3- 5 equal valid (3.07 m).

With continuous pumping of the product in a single line, the thawing halo for the same service life would be 10 m.

During cyclical reverse freezing and thawing of halos 8, the sediments of the soil in the thawing halos are partially compensated by heaving the soil during freezing.

Example. It is necessary to lay a pipeline with a diameter of 530x7 mm through the section 1 of high interlayer with thawing of soils. The length of the plot is 1 km. High-permafrost permafrost soils are composed of peat (thawing coefficient 0.12, compressibility factor 0.021, ice content due to ice inclusions 0.31). The permissible draft of the pipeline is determined by the strength analysis and is assumed to be 1.08 m. The actual draft of a continuously operating single pipeline would be 3.38 with a thawing halo of 10 m, which is much more than permissible.

The permissible thawing halo, which must be maintained during operation (from the condition of ensuring strength), is 2.01 m. The operating time of the permissible thawing halo per switch is 24.02 months.

Threads 3, 4 are laid at the calculated distance L 5 m, excluding their mutual thermal effect.

For two years, the product is pumped on line 3, while the halo is thawing

around it is 2 m, and a drawdown of 0.68 m, after which the pumped product is switched to string 4. During the two years of operation of string 4 on string 3, the permafrost in the thawing halo is fully restored 8.

Thus, during the period of operation, the number of switchings will be equal to five, while the final aura of thawing does not exceed the permissible values. Control over the formation of thawing halos can be carried out through a thermal well installed near the pipeline or by leveling the axis of the pipeline to assess the actual sludge,

The invention makes it possible to eliminate the use of special structural and technological elements for regulating the thermal interaction of the pipeline with permafrost soils, simplifies this regulation and the construction process itself.

Claims (1)

The invention method of constructing an underground pipeline in areas unstable when thawing soils, consisting in a fragment of a trench, laying in it equipped with shut-off valves of the pipeline, backfilling with a trench and regulating the size of the aureole thawing of soil around the pipeline by the impact on the pumped product, 0 characterized in that, in order to increase the operational reliability of the pipeline by limiting the defrosting aureole, within the section of unstable soils, the pipeline spans5 are and is laid at least in two lines, and the regulation of the thermal conditions of the defrostation halo is performed when it reaches in advance of a given value by switching the flow of the pumped product to the backup line, while . the threads are spaced apart from friend precluding their mutual thermal influence, and valves are installed at the boundaries of the area of unstable soils. FIG. 2