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Thawing permafrost has affected the structural integrity of buried warm pipelines in cold regions and poses an ongoing threat in the context of climate change. Therefore, characterizing variation in the engineering properties of pipeline foundation permafrost and its effect on the mechanical behavior of pipeline is important. In this paper, the ground temperature distributions around a buried warm pipeline and mechanical response of the pipeline to differential thaw settlement of foundation permafrost are investigated using thermal–mechanical sequential coupling simulation, based on the observational data collected from a selected monitoring site along the China-Russia crude oil pipelines in northeastern China. The results indicate that the thaw-induced settlement of pipeline foundation permafrost develops quickly with the formation and expansion of the thaw bulb in the first 10 years, and then increases slowly when the thaw bulb extends to the weathered granite. Differential thaw settlement will cause a significant change in the deformation and stress of the pipeline near the interface of strong and weak thaw settlement zones. When the length ratio of strong and weak thaw settlement zones is 1, the maximum stress of the pipeline with a thickness of 16 mm is approximately 45% of the allowable stress of X65 steel, and the pipeline remains safe for 30 years. However, the potential failure of the pipeline should be considered due to the continued ground thawing and warming and pipe material aging. Forthcoming research on this topic is needed to evaluate more carefully the structural integrity of buried pipelines in cold regions. [ABSTRACT FROM AUTHOR]

Human engineering activities and climate warming induce permafrost degradation in the Da Xing'anling Mountains, which may affect the distribution of permafrost and the safety of infrastructure. This study uses the electrical resistivity tomography method, in combination with field surveys and ground temperature monitoring, to investigate the distribution and degradation characteristics of permafrost and influencing factors at a typical monitoring site (MDS304) near the China-Russia Crude Oil Pipeline (CRCOP). The results show that the isolated permafrost in this area is vulnerable to further degradation because of warm oil pipelines and thermal erosion of rivers and ponds. The isolated permafrost is degrading in three directions at the MDS304 site. Specifically, the boundary between permafrost and talik is on both sides of the CRCOP, and permafrost is distributed as islands along a cross-section with a length of about 58–60 m. At present, the vertical hydrothermal influence range of the CRCOP increased to about 10–12 m. The active layer thickness has increased at a rate of 2.0 m/a from about 2.4–6.8 m to 2.5–10.8 m from 2019 to 2021 along this cross-section. Permafrost degradation on the side of the CRCOP's second line is more visible due to the river's lateral thermal erosion, where the talik boundary has moved eastward about 12 m during 2018–2022 at a rate of 3.0 m/a. It is 2.25 times the westward moving speed of the talik boundary on one side of the CRCOP's first line. In contrast, the talik boundary between the CRCOP's first line and the G111 highway also moves westward by about 4 m in 2019–2022. Moreover, the maximum displacement of the CRCOP's second line caused by the thawing of frozen soil has reached up to 1.78 m. The degradation of permafrost may threaten the long-term stability of the pipeline. Moreover, the research results can provide a useful reference for decision-makers to reduce the risk of pipeline freeze-thaw hazards. [ABSTRACT FROM AUTHOR]

The thermal state of permafrost in the present and future is fundamental to ecosystem evolution, hydrological processes, carbon release and infrastructure integrity in cold regions. In 2011, we initiated a permafrost monitoring network along the China–Russia crude oil pipeline (CRCOP) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. We compiled an integrated dataset of the ground thermal state along the CRCOP route consisting of meteorological data near the southern limit of latitudinal permafrost, ground temperature (GT) data in 20 boreholes with depths of 10.0–60.6 m, soil volumetric liquid water contents (VWCs) and 2D electrical resistivity tomography (ERT) data at different sites. Results demonstrate a permafrost warming during 2011–2020 in the vicinity of the southern limit of latitudinal permafrost, as manifested by rising GTs at almost all depths in response to climate warming. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipelines. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as an insulation layer and thermosyphons. The in situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro–thermal–mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.272357; Li, 2022). [ABSTRACT FROM AUTHOR]

The China–Russia crude oil pipeline (CRCOP) has been in operation for over ten years. Field observation results have shown that a thaw bulb has developed around the CRCOP which expands at a rate of more than 0.8 m∙a−1 in depth. In view of the deficits of existing measures in mitigating permafrost thaw, a new control method is proposed based on active cooling. According to the relationship between total pressure loss and the driving force of natural ventilation, the wind speed in a U-shaped air-ventilation pipe around the CRCOP is calculated. By analyzing the theoretical calculation and numerical analysis results, it is found that the influence of thermal pressure difference on the natural ventilation of the structure can be negligible, and the influences of resistance loss along the pipe and local resistance loss in the pipe are similarly negligible. Exhaust elbows greatly improve the ventilation performance of the U-shaped air-ventilated pipe. This study developed a novel structure around warm-oil pipelines in permafrost for mitigating thaw settlement along the CRCOP and other similar projects across the world. [ABSTRACT FROM AUTHOR]

The China–Russia crude oil pipeline (CRCOP) traverses rivers, forests, and mountains over permafrost regions in northeastern China. Water accumulates beside the pipe embankment, which disturbs the hydrothermal balance of permafrost underlying the pipeline. Ground surface flows along the pipeline erode the pipe embankment, which threatens the CRCOP's operational safety. Additionally, frost heave and thaw settlement can induce differential deformation of the pipes. Therefore, it is necessary to acquire the spatial distribution of water features along the CRCOP, and analyze the various hazard probabilities and their controlling factors. In this paper, information regarding the permafrost type, buried depth of the pipe, soil type, landforms, and vegetation were collected along the CRCOP every 2 km. Ponding and erosive damage caused by surface flows were measured via field investigations and remote sensing images. Two hundred and sixty-four pond sites were extracted from Landsat 8 images, in which the areas of 46.8% of the ponds were larger than 500 m2. Several influential factors related to freeze–thaw hazards and erosive damage were selected and put into a logistic regression model to determine their corresponding risk probabilities. The results reflected the distributions, and forecasted the occurrences, of freeze–thaw hazards and erosive damage. The sections of pipe with the highest risks of freeze–thaw and erosive damage accounted for 2.4% and 6.7%, respectively, of the pipeline. Permafrost type and the position where runoff encounters the pipeline were the dominant influences on the freeze–thaw hazards, while the runoff–pipe position, buried depth of the pipe, and landform types played a dominant role in erosive damage along the CRCOP. Combined with the geographic information system (GIS), field surveys, image interpretation and model calculations are effective methods for assessing the various hazards along the CRCOP in permafrost regions. [ABSTRACT FROM AUTHOR]

• Multi-type data characterized the disturbance of the China–Russia Crude Oil Pipeline (CRCOP) on the permafrost environment. • Mapped the development of the talik around pipelines under the influence of multiple factors. • Permafrost thawing along the CRCOP caused topographic reshaping and the regular distribution of ponds. • Synergistic changes of underground permafrost and surface features. Engineering activities in permafrost regions have a major impact on the local permafrost environment. The construction and operation of the China-Russia Crude Oil Pipeline (CRCOP) have changed the surface conditions and the soil's thermal state. However, the response of the permafrost environment to CRCOP is less studied. This article carries out ground temperature monitoring, ground surface deformation (GSD) and pipeline deformation observations, electrical resistivity tomography (ERT) measurements, and unmanned aerial vehicle (UAV) surveys to study permafrost thawing, talik development, topographic change, and pond distribution. The results indicated that the oil temperature has increased yearly and the permafrost around the pipeline has degraded quickly. The artificial permafrost table has decreased at a rate of 0.68 m/a at a location 2 m away from the center of the pipeline, and reached −11.4 m deep by 2022. The talik around CRCOP I was larger than that around CRCOP II and the two taliks were gradually approaching each other. Permafrost-thawing-induced pipeline subsidence and surface settlement have led to thermokarst depressions and water accumulation. The sinking rates of CRCOP I and II are approximately 0.2 m/a and 0.45 m/a, respectively. The ground surface settlement rate on the right-of-way of the pipeline (on-ROW) is about 5.49 cm/a. Settlement rate in ponding areas is 8.18 cm/a, significantly larger than 4.81 cm/a in non-ponding areas. The ponding area on-ROW accounts for 67.4 % and it on CRCOP I is larger than that on CRCOP II. Pipeline construction, high oil temperature, and permafrost thawing have led to the development of geohazards, which have potential to be worsen under the influence of fires, climate warming, and human activities. Multi-type data provides ground verification for satellite images to extract deformation and ponding information along pipelines, and provides a scientific basis for assessing the thermal impact of pipelines and geohazard development. [ABSTRACT FROM AUTHOR]

The first China-Russia crude oil pipeline (CRCOP-I) and the second China-Russia crude oil pipeline (CRCOP-II) went into operation in January 2011 and January 2018, respectively. On-site monitoring data have indicated that the seasonal thawing depth (STD) of a borehole 2 m away from CRCOP-I reached 10.8 m by the end of 2021. To improve mitigation measures of thaw settlement, an inverted T-shaped crushed-rock pipeline embankment (ITCPE) is proposed in this study. The long-term thermal activity of three types of pipeline embankments is predicted and compared with the underground structure. This study finds that none of the current pipeline structures has solved the thaw settlement issue for the CRCOP, whether with insulation layers, in an unprotected pipeline embankment (UPE), or in a traditional horizontal crushed-rock pipeline embankment (THCPE). However, the cross-ventilation attained in the proposed approach did mitigate thawing. It is estimated that after 50 years of operation, the natural permafrost table will be 2.9 m deep, whereas the proposed ITCPE central pipeline embankment could maintain the artificial permafrost table at a depth of 0.7 m. This study provides technical support for the CRCOP and provides a reference for the design and maintenance of other pipeline projects in permafrost areas worldwide. • In-site warning system and ERT testing reveal that the permafrost surrounding the CRCOP is thawing. • Insulation cannot change the thermal evolution trend of the permafrost surrounding the CRCOP. • A newly designed ITCPE system for thaw settlement mitigation is employed. • ITCPE is effective at mitigating thaw settlement and non-uniform deformation using ambient cool energy. [ABSTRACT FROM AUTHOR]

The China–Russia crude oil pipeline (CRCOP) has been in operation for over 10 years. In order to obtain the necessary data for pipeline research and provide real-time warning for pipeline operation, an in-situ composite monitoring system of pipeline–permafrost interaction along the CRCOP was established. Monitoring results has shown that a thaw bulb develops around the CRCOP, urging consolidation in strongly thawed segments. The key to maintaining the stability of warm-oil pipelines buried in permafrost is to mitigate permafrost thaw and keep the differential settlement of the pipeline in its allowable strain range. To maintain the stability of CRCOP, a novel technique is proposed to mitigate thaw settlement of underlying permafrost, preventing pipeline failure and oil spills and in turn environmental disaster. Its cooling performance is evaluated based on indoor model testing platform using in-situ monitoring data including oil temperature, ground temperature and air temperature. The initiation and development of a thaw bulb was observed around the CRCOP, urging consolidation in strongly thawed segments. Additionally, an indoor model test is conducted to verify the cooling effect of a U-shaped air ventilation duct (U-AVD). The results show that the U-AVD is conducive to mitigating permafrost thaw and removing the thaw bulb around the buried pipeline in the cold season. The findings in this article can provide a reference for studies on the CRCOP and other pipeline engineering in permafrost regions. • In-site monitoring system reveal that the permafrost surrounding the CRCOP is thawing. • A novel U-AVD is employed and its heat transfer performance is assessed. • The thaw bulb surrounding pipelines is consistently present due to pipeline heat through the year. • U-AVD is effective at mitigating permafrost degradation using ambient cool energy. [ABSTRACT FROM AUTHOR]

The comparative advantage among countries determines their trade relations pattern and even regional governance mode, which has profound significance for understanding the Belt and Road (B&R) initiative. B&R has been gaining attention internationally since its proposal. This paper aims to investigate the structure and influence factors of trade competitive advantage networks of the countries along the B&R (BR-TCANs). Different from the existing literature, this paper constructs the directed trade comparative advantage index (DTCA), and establishes BR-TCANs by using the bilateral trade data in 1993–2018 collected from the United Nations Commodity Trade Statistics Database (UNCOMTRADE). Subsequently, based on complex network approach, we analyze the structure and its evolution characteristics of BR-TCANs, and then discuss the factors that influence the formation of BR-TCANs' structure by using exponential random graph models (ERGMs). The results show that there are obvious small-world and reciprocity characteristics on BR-TCANs. Both Turkey and Russia have the largest scope of trade competitive advantages, and China has the strongest intermediation ability in BR-TCANs. BR-TCANs form three communities, including the West, the North and the South. The formation of BR-TCANs is greatly influenced by popularity, clustering, reciprocity and self-reinforcing mechanism, and is manifested in the heterogeneity of GDP and FDI and in the homogeneity of population and trade openness. Countries with higher GDP, spoken language and currency advantages are more likely to establish trade competitive advantages with others. Accordingly, the BR-TCANs are embedded in the networks of common language, currency, geographic boundary and free trade agreements. [ABSTRACT FROM AUTHOR]

The China–Russia Crude Oil Pipeline (CRCOP) has been in operation for more than ten years, and its oil temperature has been increasing annually. Problems with ground surface subsidence and pipeline settlement were found in geological investigations along the CRCOP, indicating the risk of pipeline instability. In this study, a system was established to monitor pipeline–permafrost interactions along the CRCOP. It was found that the seasonal thawing depth (STD) of a borehole 2 m away from the horizontal line of the CRCOP reached about 11 m in 2022. Based on the on-site measured boundary, a laboratory experiment was conducted to study the evolution of the thermal regime, and to investigate the cooling effect of thermosyphons. The results indicated the consistent existence of a thaw bulb surrounding the pipeline, which was open in warm seasons but remained closed in cold seasons and expanded in three directions at different speeds. Thermosyphoning erased the thaw bulb and altered the thermal evolution of the permafrost, with a gradually decreasing STD. The results of this research can serve as a reference for thermal regime assessments of the CRCOP and thaw settlement mitigation along the CRCOP, as well as for other counterparts across the world. • In-situ monitoring reveals that the permafrost surrounding the CRCOP is warming and degrading. • A large-scale indoor pipeline–permafrost interaction test platform is established. • The thaw bulb surrounding the buried pipeline exists all year round. • The thermosyphons can change the evolution trend of the permafrost surrounding the pipeline. [ABSTRACT FROM AUTHOR]

Rapid permafrost thawing triggered by heat release from the buried warm-oil pipeline would result in the instability of the pipeline, posing a potential risk of an oil spill in permafrost regions. Therefore, how to precisely control the ground temperature to mitigate pipeline foundation permafrost from thawing is of significant importance. Thermosyphon is a widely-accepted and extensively-used countermeasure against permafrost thawing in permafrost engineering. This paper presents 3-year (2015–2018) monitored data of ground temperature and geophysical survey results conducted by electrical resistivity tomography in April 2018, to investigate the thermal stabilizing effect of thermosyphons installed nearby the China-Russia crude oil pipeline (CRCOP) and the influencing factors. Furthermore, numerical simulation tests were conducted to evaluate their long-term cooling applicability and to optimize their layout parameters. Field observations show that the thermosyphons can cool down and even freeze the thawed soil layers around the CRCOP, prohibiting the infiltration of water into the thawing front to some extent and effectively mitigating the rapid thawing of permafrost beneath the pipeline. The performance of the thermosyphons is greatly influenced by the method and time of thermosyphon installation, as well as layout parameters including the number and longitudinal spacing. Two pairs of thermosyphons with a shorter spacing are unable to control the thawing of the underlying permafrost due to the non-anticipated higher oil temperature, the thermal erosion of water ponding, and climate warming. The simulated results indicate that thermosyphons perform well in the first 5 years after installation. Thermosyphon lowers the mean annual temperature of soils surrounding it by about 2 and 1.4 times when the evaporator section length is increased by 50% and the longitudinal spacing is decreased by 0.5 m, respectively. The application of thermosyphons has proven its strength for thermally stabilizing the pipeline foundation permafrost along the CRCOP. • 3-year ground temperature data and geophysical survey results are presented. • Thermosyphon can mitigate the rapid thawing of permafrost beneath the pipeline. • Thermosyphons performs most significantly in the first five years. • Lengthening thermosyphon and decreasing spacings are favorable for the better cooling effect. [ABSTRACT FROM AUTHOR]

Multiple studies demonstrate that narrow-linear strong disturbances triggered by pipeline engineering activities have resulted in rapid permafrost degradation. However, the extent, duration, and severity of permafrost disturbances induced by two parallel buried warm-oil pipelines remain unclear. Here, we examine the thermal disturbances of the China-Russia crude oil pipelines (CRCOPs I and II) on the surrounding permafrost. Ground temperature measurements on and off the right-of-way of the CRCOPs and an electrical resistivity tomography survey were conducted at a selected high-latitude wetland site in northeastern China. The observations showed that warm oil flow in pipelines dissipated heat to the surrounding soil, resulting in the thawing of underlying permafrost accompanied by the formation and development of thaw bulbs around the pipes. Currently, the thaw bulb of CRCOP-I was about four times as large as that of CRCOP-II, mainly due to the longer 7-year working duration of CRCOP-I. To quantify the permafrost disturbances around the pipeline, a conductive heat transfer model was established. A numerical simulation of the soil thermal regime around the pipeline suggested the initial growth of the thaw bulb was quite fast but gradually slowed with time, of which the shape was modified to ellipse from a semicircle. The existence of CRCOP-II would accelerate the warming of permafrost on the CRCOP-I right-of-way due to the small separation distance between them. We expect that the thaw bulbs of the two pipelines will expand larger than previously estimated due to the adverse effects of pipeline settlement and surface water flow, sparking a wider permafrost disturbance. • Thermal permafrost disturbances caused by two parallel buried warm-oil pipelines in a high-latitude wetland were analyzed. • Initial growth of thaw bulb around the warm-oil pipeline was fast but gradually slowed with time. • Thaw bulbs will expand and eventually overlap partially as the operational period of the two pipelines proceeds, sparking a wider permafrost disturbance. [ABSTRACT FROM AUTHOR]