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In permafrost regions, buried oil pipelines have a substantial thermal impact on the surrounding permafrost due to the large temperature difference between the oil and ground. The change in the thermal regime of the permafrost may trigger frost heave and thaw settlement of the pipeline, and can even destroy the pipeline. In this paper, an example of parallel-buried pipelines is performed, and a numerical method is employed to simulate the thermal impact of pipelines on permafrost foundations for both ice-poor and ice-rich permafrost with various kinds of distances between parallel pipelines. The results show that the thermal effect caused by the operation of pipelines can increase the temperature of permafrost, as well as cause the underlying permafrost foundation to thaw gradually. The thermal impact of parallel pipelines on the permafrost foundation depends on the distance between the parallel pipelines, ice content of the permafrost, initial permafrost temperature, and so on. The degree of influence on each other decreases as the distance between parallel pipelines increases. With an insulated pipeline that has been in operation for 50 years, the thaw depths under the parallel pipelines, with distances of 5 m, 10 m, and 15 m, increase by 1.4 m, 0.4 m, and 0.1 m compared to the single pipeline in the ice-rich permafrost district with the average ground temperature being -0.5°C and the ice content being 35%. Nevertheless, there is no difference between the single and parallel pipelines if the distance is more than 20 m. The recommended distance between parallel pipelines in this district should be greater than 15 m. Different permafrost districts should set separate recommended distances, and the corresponding protective measures should be made outside the recommended distance. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Railway traverses 550 km of permafrost region. After embankment construction in 2003, considerable detrimental permafrost-related embankment deformations developed along the railway. Based on field monitoring data collected from 2005 to 2012, typical embankment deformations, as well as their mechanisms along the railway were analyzed, taking into account the thermal regime and ice content of the subgrade soil layers. Results showed that frost heave of the embankment was slight and only occurred on a few in-cut roadbeds and air convection crushed rock embankments (ACCEs) in colder permafrost regions (< -1.5 °C). It mainly developed with upward movement of the permafrost table under the roadbed during the first 3-4 years after embankment construction. Settlement of embankments was significant, and some already threaten the railway's safe operation. As ACCEs successfully cooled the shallow subgrade and underlying permafrost, embankment settlement was relatively slight and acceptable. Settlement of traditional sand gravel embankments (TSGEs) was generally greater than that of ACCEs. In warmer permafrost regions (> -0.7 °C), thaw consolidation of the underlying permafrost resulted in significant settlement on TSGEs, some of which reached 40 cm. [ABSTRACT FROM AUTHOR]

A series of indoor tests were conducted to study the changes of soil particles and pores under freezing and thawing cycles. Testing results showed that grain breakages of coarse particles occurred during freezing and thawing cycles, resulting in an increase of the Atterberg limits and specific surface area of the soil samples. Meanwhile, the pore size distribution, tested by the mercury intrusion method, was also changed during the cycles; macro pores increased, mini pores reduced, and micro pores remained roughly unchanged. The interaction of soil particles (solid phase), soil pores (gas phase), and soil water (liquid phase), namely soil's three phase components, is discussed to explore the change mechanisms of soil structures under freezing and thawing cycles. [ABSTRACT FROM AUTHOR]

A large amount of work has been conducted to study the effect of freeze-thaw cycles on the geotechnical properties of various soils. But less laboratory work has been focused on the effect of number of freeze-thaw cycles and on quantitative relationship between mechanical behavior and freeze-thaw cycles. This study undertook a series of tests including freeze-thaw (FT) (after 0, 2, 5, 11, 21, and 31 freeze-thaw cycles respectively), unconfined compression (UC) and unconsolidated-undrained triaxial compression (UUTC) tests. These tests aim to assess the influence of freeze-thaw cycles on the mechanical behavior of compacted finegrained soil, to establish correlation between the mechanical behavior and freeze-thaw cycles, and to facilitate the prediction of changes in geotechnical properties of soil. Freeze-thaw cycles notably influence the stress-strain curve reducing the UC strength by 11%, elastic modulus by 32%, and cohesion by 84% after 31 freeze-thaw cycles in comparison with those soils unexposed to freeze-thaw. The angle of internal friction is slightly increased by 1 to 2°. The weakening and deteriorating effects of freeze-thaw on the compacted fine-grained soil are confirmed. They can provide a scientific basis for design consideration of cold-region infrastructures, and for countermeasures against frost heave and thaw settlement. [ABSTRACT FROM AUTHOR]