Ninth International Conference on Permafrost ... - IARC Research

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Engineering Effect on the Thermal Status of Shallow Ground in Permafrost RegionsZhi WenState Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000Yu ShengState Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000Wei MaState Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000Qingbai WuState Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000Bo HuangQinghai Provincial Highway Research and Survey Institute, Xining Qinghai 810008, ChinaIntroductionThe construction of an embankment in permafrost regionsmay induce substantial disturbance on the heat and masstransfer balance between the ground surface and atmosphere,which results in more heat absorption in the embankment.The temperature of the permafrost underneath increaseseven if permafrost thaws, causing serious problems forembankment due to thaw settlement on the Qinghai-TibetanPlateau (Wen & Sheng 2003). The thermal status of theembankment affects directly the thermal status of permafrostunder the railway embankment, which determines theembankment stability in the permafrost regions, especiallyice-rich permafrost regions (Yu & Lai 2002).Owing to important signification of the thermal regime ofthe upper soil layer on permafrost stability, many researchershave studied the thermal regime of the natural ground onthe Qinghai-Tibetan Plateau (Xu & Ma 1984, Zhang &Zhu 1998). However, there is scarce research on heatbalance and annual heat incomes and expenses of railwayembankments. To know about the influence of engineeringactivities on the thermal regime of the natural ground,dynamic monitoring using dataloggers made in CompbellCompany for temperature and heat flux in the upper activelayer was carried out during August 2002, making it possibleto use quantificational method analyses of the influence ofengineering activities.General Situation of the Test SitesThe test site is situated between Kekexili and Fenghuoshanalong the Qinghai-Tibetan Railway on the Qinghai-TibetanPlateau. Dynamic monitor sections of railway embankmentand natural ground were set up on August 2002. Eachsection may measure heat flux and temperature of shallowground simultaneously. Instruments used in two sectionswere self-calibrating heat flux sensor, temperature sensor,and datalogger and the readings were taken once half hour.The temperature probe may measure the temperature at thedepth of 2.0 cm, 5.0 cm, 10.0 cm, 20.0 cm, and 50.0 cmfrom ground surface. The depth of heat flux placed was 20.0cm from ground surface. Taking the difference of heat fluxat two sides of the embankment into consideration, therewas one self-calibrating heat flux sensor at each side of twosections and the data of heat flux were the even value of twosensors.Variation Character of Soil TemperatureAfter railway embankment construction, many conditionswere changed compared to natural ground, such as surfaceconditions (vegetation, albedo, etc.), soil moisture content,and soil component, which affected radiation absorptionof surface and its transfer process downwards certainly. Asseen in Figure 1, the soil temperature under the embankmentsurface at a depth of 50.0 cm was 2°C higher than that of thenatural ground and had same phase location under similarclimatic conditions (embankment testing site was close tonatural ground site). Apparently, the phase and variationcurrent of soil temperature was similar between two sites,which was due to some same conditions for two sites, suchas climatic conditions, etc., that had nothing to do withengineering activities. However, the soil temperature at theembankment site was 2°C higher than that of the naturalground site if other conditions stayed the same, whichwas affected by engineering activities distinctly. Afterengineering construction, vegetation in the natural groundwas destroyed, and the soils type, soils component, and itsmoisture content were changed, which increased the radiationabsorption and decreased the evaporation water content. Ina word, a high temperature boundary was brought to bearon the surface, which augmented the heat exchange andaccelerated the permafrost degradation. Due to engineeringactivities, thawed core below embankment came into beingand thawing settlement began.Temperature/ ℃13119722-Aug 24-Aug 26-Aug 28-Aug 30-Aug 1-Sep 3-Sep 5-SepTime/dNatural groundRailway embankmentFigure 1. The contrastive temperature curves between the railwayfoundation and the natural ground at 50 cm depth.339
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tHeat flux/(w/m^2)155-5-15-2530-Aug 31-Aug 1-Sep 2-Sep 3-Sep 4-SepTime/dRailway embankmentNatural groundFigure 2. The contrastive heat flux curves between the railwayfoundation and the natural ground at 50 cm depth in the warmseason.Heat flux/(w/m^2)1050-5-10-15-208-Jan 10-Jan 12-Jan 14-JanTime/dRailway embankmentNatural groundFigure 3. The contrastive heat flux curves between the railwayfoundation and the natural ground at 50 cm depth in the coldseason.The Variation Character of Soil Heat FluxFigures 2 and 3 show the soil heat fluxes of two sites ata depth of 20 cm in the warm season and the cold season,respectively. The observed results of soil heat fluxes at twosites showed that there were distinct differences between theembankment site and the natural ground site (Figs. 2 and 3).The soil heat flux at the natural ground site varied mild, whilethe soil heat flux at the same depth of the embankment sitevaried great. In addition, the daily amplitude of heat flux atthe natural section was smaller than that of the embankmentsection at the same depth.It can also be seen from Figures 2 and 3 that there weretwo processes (heat release state and heat absorption state)for the soil heat flux at a depth of 20 cm in the warm season,whatever under embankment and under natural ground. Asfor the cold season, the soil heat flux at the natural groundsite was in the heat release state invariably. In addition, wealso found that the daily variation amplitude of soil heat fluxin the cold season was smaller than that in the warm season,and the daily variation amplitude of soil heat flux in the coldseason was approximately one-half to two-thirds of that inwarm season.when the temperature and the moisture probes will be installedsimultaneously. Based on testing results and foregoinganalyses, some useful conclusions can be drawn. The soiltemperature under the embankment surface at a depth of 50cm was 2°C higher than that of natural ground, and they hadthe same phase location under similar climatic conditions,which was affected by engineering activities distinctly. Thedaily variation amplitude of soil heat flux at the naturalground site was smaller than that of the embankment site,and the variation at the natural ground site was even more. Inaddition, the soil heat flux at the embankment site was moresensitive to the change of air temperature and tended more tobe disturbed by the environment. There were two processes(heat release state and heat absorption state) for soil heatflux at a depth of 20 cm in the warm season, whatever underembankment and under natural ground. The daily variationamplitude of soil heat flux in the cold season was smaller thanthat in the warm season, and the daily variation amplitude ofsoil heat flux in the cold season was approximately one-halfto two thirds of that in the warm season.AcknowledgmentsThe research was supported by a grant of the WesternProject Program of the CAS (Grant No. KZCX2-XB2-10),by the Graduate Student Innovation Program of the CASgranted to Dr. Zhi Wen, and by Opening Foundation of StateKey Laboratory of Frozen Soil Engineering.ReferencesWen, Z., Sheng, Y. & Wu, Q. 2003. Dynamic monitoring ofthermal state for shallow ground in Qinghai-TibetanRailway embankment. China Journal of RockMechanics and Engineering 22(2): 2664-2668.Xu, Z. & Ma, Y. 1986. Calculation of soil heat flux onQinghai-Tibetan plateau and analysis of stabilityof climate generalization method. Scientific testingpaper volume on Qinghai-Tibetan plateau climate.Beijing: Science Press, 35-45.Yu, W., Lai, Y. & Niu F. 2002. Temperature field featuresin the laboratory experiment of the ventilated railwayembankment in permafrost regions. Journal ofGlaciology and Geocryology 22(5): 601-607.Zhang, J., Zhu, B. et. al. 1998. Process in Climate Scienceof Qinghai-Tibetan Plateau. Beijing: Science Press,78-88.ConclusionDue to railway construction and instrument fault, longtermobservation data were not obtained. Additionally, themoisture content was not monitored. To realize the heatmoistureprocess of the active layer in permafrost regions,a heat-moisture observation plan will be performed in 2007,340
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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