The phenomena of dry shrinkage and wet expansion and frost heave and thaw settlement in expansive soils in seasonally frozen regions have caused numerous engineering problems. This study focuses on the strength degradation and slope instability in expansive soil water channels of the Northern Xinjiang water supply project. Using drying-wetting and freezing-thawing cycles as experimental conditions, the research includes moisture content monitoring at various depths to analyze soil moisture variation patterns during different stages. Additionally, laboratory experiments are conducted to study the effects of these cycles on non-uniform deformation, strength degradation, and microstructure damage in expansive soils. The results reveal that: 1) Under drying-wetting and freezing-thawing conditions, expansive soils at certain depths of the channel foundation exhibit significant moisture content fluctuations. The most significant variations occur during the freeze-thaw phase, establishing a phase change dynamic zone within the expansive soil. 2) Drying-wetting and freezing-thawing cycles cause significant microstructural damage in expansive soils, marked by continuous crack development and expansion with increasing cycle frequency. The soil experiences persistent dry shrinkage and wet expansion and frost heave and thaw settlement effects. In the early stages of drying-wetting and freezing-thawing action, expansive deformation significantly contributes to total deformation. However, after a certain number of cycles, both volumetric and expansive soil deformation gradually stabilize. 3) Expansive soils exhibit varying degrees of degradation in shear strength and strength parameters. Cohesion degrades more significantly, following an exponential decrease, while the internal friction angle experiences a less pronounced reduction. In the early stages of dry-wet and freeze-thaw cycles, cohesion degradation accounts for 41.2% to 48.6% of the total degradation rate. The significant decrease in soil cohesion leads to shallow landslides in expansive soil slopes of channel foundations, highlighting the crucial role of cohesion in slope instability.

Pipeline corridors have been rapidly increasing in length and density because of the ever growing demand for crude oil and natural gas resources in hydrocarbon-rich permafrost regions. Pipeline engineering activities have significant implications for the permafrost environment in cold regions. Along these pipeline corridors, the shrubification in the right-of-way (ROW) has been extensively observed during vegetation recovery. However, the hydrothermal mechanisms of this ROW shrubification have seldom been studied and thus remain poorly understood. This paper reviews more than 112 articles mainly published from 2000 to 2022 and focuses on the hydrothermal mechanisms of shrubification associated with environmental changes induced by the rapidly degrading permafrost from pipeline construction and around the operating pipelines under a warming climate. First, the shrubification from pipeline construction and operation and the ensuing vegetation clearance are featured. Then, key permafrost-related ROW shrubification mechanisms (e.g., from the perspectives of warmer soil, soil moisture, soil type, soil nutrients, topography and landscapes, and snow cover) are discussed. Other key influencing factors on these hydrothermal and other mechanisms are hierarchically documented as well. In the end, future research priorities are identified and proposed. We call for prioritizing more systematic and in-depth investigations and surveys, laboratory testing, long-term field monitoring, and numerical modeling studies of the ROW shrubification along oil and gas pipelines in permafrost regions, such as in boreal and arctic zones, as well as in alpine and high-plateau regions. This review can improve our understanding of shrubification mechanisms under pipeline disturbances and climate changes and help to better manage the ecological environment along pipeline corridors in permafrost regions.