Saline soils are significantly affected by water-salt phase changes,evaporation,and groundwater during seasonal freezing and thawing.For the study of physical and mechanical properties of saline soils,solubility is an...Saline soils are significantly affected by water-salt phase changes,evaporation,and groundwater during seasonal freezing and thawing.For the study of physical and mechanical properties of saline soils,solubility is an important indicator that varies with temperature.However,there have been very limited computational studies on solubility at low temperatures.The model for calculating the solubility of Na_(2)SO_(4)-NaCl-H_(2)O ternary system under low temperature conditions was constructed in this paper,based on the Pitzer and BET models.Improvements were made to the parametersФandγin the Pitzer model,while improvements were made to the parameters c,r,and aw in the BET model.The solubility changes within the range of 273.15 K–373.15 K were calculated and validated by combining them with indoor experiments.It was found that both the improved Pitzer model and BET model accurately predicted relative equilibrium solubility data of the Na_(2)SO_(4)-NaCl-H_(2)O ternary system at temperatures ranging from 273.15 K to 373.15 K.Additionally,compared with the Pitzer model,the BET model had advantages such as easy parameter acquisition and wider application range.The findings from this research hold great significance for understanding the process and patterns of salt analysis during soil freeze-thaw cycles as well as providing a scientific foundation for further comprehension of phase change laws and physical properties related to saline soils.展开更多
The original landform along the China Russia Crude Oil Pipeline(CRCOP,line 2)was disturbed during installation of pavement for the pipeline.Forest and vegetation coverage is dense,and runoff develops along the pipe.Si...The original landform along the China Russia Crude Oil Pipeline(CRCOP,line 2)was disturbed during installation of pavement for the pipeline.Forest and vegetation coverage is dense,and runoff develops along the pipe.Since the opera tion of the CRCOP(line 2)began in 2018,ponding has appeared on both sides of the pipeline.If there is no drainage,ponding can hardly dissipate,due to the low permeability of the permafrost layer.With the supply of surface flow and the transportation of oil at positive temperatures,ponding promotes an increase in temperature and changes the boundary ther mal conditions of the pipeline.Meanwhile,when the ponding freezes and thaws,frost heave threatens operational safety of the pipeline.Furthermore,the ponding can affect the thermal condition of line 1.In this paper,the distribution of pond ing along the CRCOP was obtained by field investigation.The type and cause of ponding were summarized,and the catch ment and stream order were extracted by the Digital Elevation Model(DEM).According to the statistical results in attri butes for topographic factors,it is known that ponding along the pipeline is relative to elevation,slope,aspect,and the Topographic Wetness Index(TWI).Water easily accumulates at altitudes of 300450 m,slopes within 3°5°,aspect in the northeast or south,TWI within 1316,flow direction in north east south,and flow length within 90150 km.This paper proposes a theoretical basis for the cause and characteristics of ponding along the pipeline.展开更多
Buried pipelines are widely used for transporting oil in remote cold regions. However, the warm oil can induce considerable thermal influence on the surrounding frozen soils and result in severe maintenance problems. ...Buried pipelines are widely used for transporting oil in remote cold regions. However, the warm oil can induce considerable thermal influence on the surrounding frozen soils and result in severe maintenance problems. This paper presents a case study of the thermal influence of ponding and buried warm-oil pipelines on permafrost along the China-Russia Crude Oil Pipeline(CRCOP) in Northeast China. Since its operation in 2011, the operation of the warm-oil pipelines has led to rapid warming and thawing of the surrounding permafrost and development of sizable ponding along the pipeline route,which, in return, exacerbates the permafrost degradation. A field study was conducted along a 400-km long segment of the CRCOP in permafrost regions of Northeast China to collect the location and size information of ponding. A two-dimensional heat transfer model coupled with phase change was established to analyze the thermal influence of ponding and the operation of warm-oil pipelines on the surrounding permafrost. In-situ measured ground temperatures from a monitoring site were obtained to validate the numerical model. The simulation results show that ponding accelerates the development of the thaw bulb around the pipeline. The maximum thaw depth below the pipeline increases from 4 m for the case without ponding to 9 m for the case with ponding after 50 years of operation, and ponding directly above the pipe induces the maximum thaw depth. Engineering measures should be adopted to control the size or even eliminate surface water-rich ponding for the long-term performance of buried warm-oil pipelines.展开更多
Creep is an important mechanical behavior of frozen soils, one which can cause many problems for the infrastructures in permafrost regions on the Qinghai-Tibetan Plateau. To access the natural creep properties of in s...Creep is an important mechanical behavior of frozen soils, one which can cause many problems for the infrastructures in permafrost regions on the Qinghai-Tibetan Plateau. To access the natural creep properties of in situ permafrost for explaining the engineering instability and predicting long-term deformation, conducting field tests is necessary. The paper reports on a group of plate loading tests we carried out over many years on the Qinghai-Tibetan Plateau. The results show that the ground temperature at the loading plates ranged from-0.29 °C to-3.03 °C, and the mean annual ground temperature increased year by year in a linear fashion. Affected by the ground-temperature variations, two forms of deformation curves, a step-form and a wave-form occurred, depending on the relative extent of settlement in warm seasons and frost heave in cold seasons. Overall, the deformations of permafrost were characterized by settlement. The deformation magnitudes and curve styles of permafrost are different at different locations attributing to the influence of ground temperature and moisture content. Due to the existence of much unfrozen water in warm frozen soils, consolidation resulting from migration of unfrozen water along seepage channels may play a significant role in the settlement of permafrost. The research can provide a credible reference for engineering in the permafrost regions and the numerical computation of settlement.展开更多
As a unique hydro-geological phenomenon in permafrost regions,the seepage of supra-permafrost groundwater will carry a large amount of heat and cause differential settlement in the embankment.This paper presents the r...As a unique hydro-geological phenomenon in permafrost regions,the seepage of supra-permafrost groundwater will carry a large amount of heat and cause differential settlement in the embankment.This paper presents the results of a field study monitoring the supra-permafrost groundwater levels on both sides of an embankment in permafrost regions.It describes a two-dimensional coupled hydro-thermal model and uses it to analyze the influence of seepage on its temperature field considering climate warming.The results show that seepage exacerbates permafrost thawing and thickens the active layer.The thermal influence on the sunny side of the embankment toe is more significant than that on the shady side,which will cause differential settlement in the embankment.After 50 years of operation,the embankment soil temperature with seepage during freezing is 0.2C warmer than that without seepage,and the thermal influence diminished with the increase in depth.Additionally,seepage influences the thermal regime in vertical and horizontal directions of the embankment.During freezing seasons,the thaw depth increases,and the horizontal thaw range decreases.During thawing seasons,the thaw range grows both vertically and horizontally.展开更多
基金supported by the National key research&development program of China(Grant no.2021YFD1900600)the National Natural Science Foundation of Ningxia(2023AAC05014)+1 种基金the Ningxia Key Research and Development Program(Special Talents)(2023BSB03021)the Scientific Research Program of University of Ningxia Education Department(NYG2024049)。
文摘Saline soils are significantly affected by water-salt phase changes,evaporation,and groundwater during seasonal freezing and thawing.For the study of physical and mechanical properties of saline soils,solubility is an important indicator that varies with temperature.However,there have been very limited computational studies on solubility at low temperatures.The model for calculating the solubility of Na_(2)SO_(4)-NaCl-H_(2)O ternary system under low temperature conditions was constructed in this paper,based on the Pitzer and BET models.Improvements were made to the parametersФandγin the Pitzer model,while improvements were made to the parameters c,r,and aw in the BET model.The solubility changes within the range of 273.15 K–373.15 K were calculated and validated by combining them with indoor experiments.It was found that both the improved Pitzer model and BET model accurately predicted relative equilibrium solubility data of the Na_(2)SO_(4)-NaCl-H_(2)O ternary system at temperatures ranging from 273.15 K to 373.15 K.Additionally,compared with the Pitzer model,the BET model had advantages such as easy parameter acquisition and wider application range.The findings from this research hold great significance for understanding the process and patterns of salt analysis during soil freeze-thaw cycles as well as providing a scientific foundation for further comprehension of phase change laws and physical properties related to saline soils.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA2003020102)the National Natural Science Foundation of China (No. 41630636 and No. 41772325)the China Postdoctoral Science Foundation (No. 2019M653797)
文摘The original landform along the China Russia Crude Oil Pipeline(CRCOP,line 2)was disturbed during installation of pavement for the pipeline.Forest and vegetation coverage is dense,and runoff develops along the pipe.Since the opera tion of the CRCOP(line 2)began in 2018,ponding has appeared on both sides of the pipeline.If there is no drainage,ponding can hardly dissipate,due to the low permeability of the permafrost layer.With the supply of surface flow and the transportation of oil at positive temperatures,ponding promotes an increase in temperature and changes the boundary ther mal conditions of the pipeline.Meanwhile,when the ponding freezes and thaws,frost heave threatens operational safety of the pipeline.Furthermore,the ponding can affect the thermal condition of line 1.In this paper,the distribution of pond ing along the CRCOP was obtained by field investigation.The type and cause of ponding were summarized,and the catch ment and stream order were extracted by the Digital Elevation Model(DEM).According to the statistical results in attri butes for topographic factors,it is known that ponding along the pipeline is relative to elevation,slope,aspect,and the Topographic Wetness Index(TWI).Water easily accumulates at altitudes of 300450 m,slopes within 3°5°,aspect in the northeast or south,TWI within 1316,flow direction in north east south,and flow length within 90150 km.This paper proposes a theoretical basis for the cause and characteristics of ponding along the pipeline.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA2003020102)the China Postdoctoral Science Foundation(No.2019M653797)+1 种基金the National Natural Science Foundation of China(No.41630636 and No.41772325)the Major Program of the Bureau of International Cooperation,the Chinese Academy of Sciences(131B62KYSB20170012).
文摘Buried pipelines are widely used for transporting oil in remote cold regions. However, the warm oil can induce considerable thermal influence on the surrounding frozen soils and result in severe maintenance problems. This paper presents a case study of the thermal influence of ponding and buried warm-oil pipelines on permafrost along the China-Russia Crude Oil Pipeline(CRCOP) in Northeast China. Since its operation in 2011, the operation of the warm-oil pipelines has led to rapid warming and thawing of the surrounding permafrost and development of sizable ponding along the pipeline route,which, in return, exacerbates the permafrost degradation. A field study was conducted along a 400-km long segment of the CRCOP in permafrost regions of Northeast China to collect the location and size information of ponding. A two-dimensional heat transfer model coupled with phase change was established to analyze the thermal influence of ponding and the operation of warm-oil pipelines on the surrounding permafrost. In-situ measured ground temperatures from a monitoring site were obtained to validate the numerical model. The simulation results show that ponding accelerates the development of the thaw bulb around the pipeline. The maximum thaw depth below the pipeline increases from 4 m for the case without ponding to 9 m for the case with ponding after 50 years of operation, and ponding directly above the pipe induces the maximum thaw depth. Engineering measures should be adopted to control the size or even eliminate surface water-rich ponding for the long-term performance of buried warm-oil pipelines.
基金supported by the National Natural Science Foundation of China (No. 41401087)the Independent Foundation of the State Key Laboratory of Frozen Soil Engineering (No. SKLFSE-ZT-35)+1 种基金the Foundation for Excellent Youth Scholars of CAREERI, CAS (No. Y551C91001)the Technology Program of Qinghai Traffic Science Institute (No. Y490E21001)
文摘Creep is an important mechanical behavior of frozen soils, one which can cause many problems for the infrastructures in permafrost regions on the Qinghai-Tibetan Plateau. To access the natural creep properties of in situ permafrost for explaining the engineering instability and predicting long-term deformation, conducting field tests is necessary. The paper reports on a group of plate loading tests we carried out over many years on the Qinghai-Tibetan Plateau. The results show that the ground temperature at the loading plates ranged from-0.29 °C to-3.03 °C, and the mean annual ground temperature increased year by year in a linear fashion. Affected by the ground-temperature variations, two forms of deformation curves, a step-form and a wave-form occurred, depending on the relative extent of settlement in warm seasons and frost heave in cold seasons. Overall, the deformations of permafrost were characterized by settlement. The deformation magnitudes and curve styles of permafrost are different at different locations attributing to the influence of ground temperature and moisture content. Due to the existence of much unfrozen water in warm frozen soils, consolidation resulting from migration of unfrozen water along seepage channels may play a significant role in the settlement of permafrost. The research can provide a credible reference for engineering in the permafrost regions and the numerical computation of settlement.
基金the National Natural Science Foundation of China(Grant No.42001065)Open Project of State Key Laboratory of Frozen Soils Engineering(Grant No.SKLFSE202106)+1 种基金the Natural Science Foundation of Ningxia(2022AAC03052)the University First-Class Discipline Construction Project of Ningxia,China(Grant No.NXYLXK2021A03).
文摘As a unique hydro-geological phenomenon in permafrost regions,the seepage of supra-permafrost groundwater will carry a large amount of heat and cause differential settlement in the embankment.This paper presents the results of a field study monitoring the supra-permafrost groundwater levels on both sides of an embankment in permafrost regions.It describes a two-dimensional coupled hydro-thermal model and uses it to analyze the influence of seepage on its temperature field considering climate warming.The results show that seepage exacerbates permafrost thawing and thickens the active layer.The thermal influence on the sunny side of the embankment toe is more significant than that on the shady side,which will cause differential settlement in the embankment.After 50 years of operation,the embankment soil temperature with seepage during freezing is 0.2C warmer than that without seepage,and the thermal influence diminished with the increase in depth.Additionally,seepage influences the thermal regime in vertical and horizontal directions of the embankment.During freezing seasons,the thaw depth increases,and the horizontal thaw range decreases.During thawing seasons,the thaw range grows both vertically and horizontally.
