Monitoring and analysis of ground temperature and deformation within Qinghai-Tibet Highway subgradein permafrost region

In order to study the stability of the Qinghai-Tibet Highway embankment at Chumaerhe in the permafrost region of northwest China, the ground temperature and deformation at different depths were monitored under the left and right shoulders of the embankment where thermosyphons were set up only on the left shoulder. Based on the monitored data, characteristics of ground temperature and deformation of the left and right shoulders are analyzed and discussed. The results show that the start time of freezing or thawing of the seasonal active layer was about one to two months later than that of the embankment body itself. The stability of each shoulder was mainly controlled by the settlement of different soil layers,whereasfrost heave of soil had scarcely any effect on the stability of the embankment. For the left shoulder, the settlement was mainly influenced by the seasonal active layer and then by the embankment body itself,due to freeze-thaw cycles which may change the soil properties; however, the permafrost layer remained fairly stable. For the right shoulder, creep of the warm permafrost layer was the main influence factor on its stability, followed by settlement of embankment body itself, and finally settlement of the seasonal active layer. Compared with the deformation of the left shoulder, the permafrost layer under the right shoulder was less stable, which indicates that the thermosyphons had a significantly positive effect on the stability of warm permafrost.     

Soil temperatures and stability of ice-cemented ground in the McMurdo Dry Valleys, Antarctica

Year-round temperature measurements at 1600 m elevation during 1994 in the Asgard Range Antarctica, indicate that the mean annual frost point of the ice-cemented ground, 25 cm below the surface, is -21.7 +/- 0.2 degrees C and the mean annual frost point of the atmosphere is -27.5 +/- 1.0 degrees C. The corresponding mean annual temperatures are -24.9 degrees C and -23.3 degrees C. These results imply that there is a net flux of water vapour from the ice to the atmosphere resulting in a recession of the ice-cemented ground by about 0.4-0.6 mm yr-1. The level of the ice-cemented permafrost is about 12 cm below the level of dry permafrost. The summer air temperatures would have to increase about 7 degrees C for thawing temperatures to just reach the top of the subsurface ice. Either subsurface ice at this location is evaporating over time or there are sporadic processes that recharge the ice and maintain equilibrium over long timescales.     

积沙影响下伏冻土的水热耦合模型研究

青藏高原地区冻土正呈退化趋势,除气候变化、人为活动的影响外,沙漠化也被认为是冻土退化的原因之一,但仍存在较大争议。基于不饱和土渗流和热传导理论,结合CoLM和Coup-Model模型,初步构建了积沙-冻土-水热概念模型和耦合模型。并在两模型的基础上,讨论了沙层反射率、积沙体热容量、积沙体厚度和沙的传热率等参数对下伏冻土的热影响过程。结果表明,沙层的反射率、地面发射率均高于天然地表,沙层接受的热量较天然地表偏少;积沙地表下的沙层和活动层能截留更多热量,使冻结层获得的热量相对减少;沙的导热性较差,导致积沙地表下地温变化出现延迟,从而延缓冻土退化;同时,积沙无论厚薄,都将起到延缓冻土退化的作用。因而,沙漠化对青藏高原冻土退化的影响可能较小,但全面揭示沙漠化对冻土的影响仍需深入研究。     

清代华北地区冬半年温度变化重建与分析

利用清代地方志中的异常初、终霜记载,根据器测时期华北初、终霜的早、晚与温度变化的关系,重建了1646-1910 年华北地区时间分辨率为5 年的冬半年温度距平序列,分析了期间的冷暖变化特征.结果表明：清代华北地区气候以寒冷为主要特征,冬半年温度平均较现代(1951-1980 年)约低0.55℃,最冷5 年(1656-1660 年)较现代约低1.42℃;清代华北地区冬半年气候存在“冷-暖-冷”的世纪波动,两个寒冷时段起讫时间分别为1646-1700 年(平均较现代约低0.77℃)和1781-1910 年(平均较现代约低0.58℃),1701-1780 年虽然相对较暖,但冬半年温度仍较现代略低(平均较现代约低0.36℃);从更高时间分辨率看,清代冷暖时段内同样存在较小的波动,清后期寒冷时段出现了两个“冷谷”.     

Analysis about the influence on the thermal regime in permafrost regions with different underlying surfaces

In the last several decades, the underlying surface conditions on the Qinghai-Tibet Plateau have changed dramatically, causing permafrost degradation due to climate change and human activities. This change severely influenced the cold regions environment and engineering infrastructure built above permafrost. Permafrost is a product of the interaction between the atmosphere and the ground. The formation and change of permafrost are determined by the energy exchange between earth and atmosphere system. Fieldwork was performed in order to learn how land surface change influenced the thermal regime in permafrost regions. In this article, the field data observed in the Fenghuo Mountain regions was used to analyze the thermal conditions under different underlying surfaces on the Qinghai-Tibet Plateau. Results show that underlying surface change may alter the primary energy balance and the thermal conditions of permafrost. The thermal flux in the permafrost regions is also changed, resulting in rising upper soil temperature and thickening active layer. Vegetation could prevent solar radiation from entering the ground, cooling the ground in the warm season. Also, vegetation has heat insulation and heat preservation functions related to the ground surface and may keep the permafrost stable. Plots covered with black plastic film have higher temperatures compared with plots covered by natural vegetation. The reason is that black plastic film has a low albedo, which could increase the absorbed solar radiation, and also decrease evapotranspiration. The ＂greenhouse effect＂ of transparent plastic film might effectively reduce the emission of long-wave radiation from the surface, decreasing heat loss from the earth＇s surface, and prominently increasing ground surface temperature.     

THERMALLY DRIVEN SORPTION,DESORPTION, AND MOISTURE MIGRATION IN THE ACTIVE LAYER IN CENTRAL ALASKA

Combined observations of hourly soil temperature and electric potential, the latter converted to a relative index of soil-water solute concentration, yield information on the physical chemistry of near-surface frost effects. Solute concentration near the descending 0° C isotherm in the refreezing active layer above permafrost is divided into three distinct zones: (1) an ion-enriched zone in the unfrozen active layer that precedes the penetrating freezing front; (2) an ion-purified desorbed zone at the freezing front that is the source region of the downward-expelled ions and water; and (3) a hydrologically isolated subfreezing zone of enhanced solute concentration located above the freezing isotherm. High-frequency fluctuations superimposed on these general patterns are traceable to vapor migration driven by surface thermal fluctuations. These effects diminish at temperatures below about -0.4° C, as permeability decreases with soil-ice formation. The combined temperature-solute concentration time series is used to develop sorption curves for the frozen organic and mineral soils, and indicates that approximately half of the pore water present in the mineral soil at -0.4° C had not been converted to ice at -6° C. Gradual soil desiccation over winter appears to result from outward vapor diffusion, possibly through soil cracks. [Key words: Alaska, active layer, frozen ground, soil temperature, soil water, permafrost.]     

西南极乔治王岛菲尔德斯半岛冷圈的结构特征

根据坑探、物探、测温资料和含冰量、含盐度的分析,讨论了菲尔德斯半岛的冻土上限及其垂直梯度的变化,并论证了石环区碗状冻结面的存在,提出了本区地壳冷圈的五层结构,即活动层、冻结砂砾石层、受海水渗透作用过的冻结火山岩层、无海水渗透影响的冻结火山岩层和未冻结的古陆基底层;肯定了离岸海下冻土的存在;发现了含盐量高的冻土电阻率可低达80Ω.m,并对冰缘地貌发育有抑制作用。     

Soil thermal properties and heat transfer processes near Ny-Alesund, northwestern Spitsbergen, Svalbard

The annually thawing active layer of permafrost is central to considerations of climate change consequences in arctic areas and interpretations of deep permafrost temperatures that constitute and exceptional archive of past climate change. Moreover, a sound understanding of the thermal regime of the active layer is of great interest, because all chemical, biological and physical processes are concentrated there. The author studied this layer by examining the soil physical properties and heat transfer processes that dictate soil temperatures for an arctic desert site in northwestern Spitsbergen. A wide array of soil physical properties based on field observations and laboratory measurements were defined. These include mineralogy, grain size distribution, local regolith thickness, porosity, density, typical soil moisture profile, heat capacity and thermal conductivity. Heat transfer processes were studied through modeling of soil temperatures. The heat transfer model accounted for much of the observed soil thermal regime. It was found that thermal conduction, phase change of soil water at 0°C, and changes in unfrozen water content are the primary thermal processes that explain the observed soil temperatues in this field site. Melt-water infiltration, which is often overlooked in the energy budget, causes abrupt warming events and delivers considerable energy to the soil in late spring. An increase in frequency or magnitude of infiltration events could mimic simple spring time surface warming. Advection of ground water and soil internal evaporation were found to be generally unimportant at the site studied.     

CHARACTERISTICS OF THE ACTIVE LAYERS ON FILDES PENINSULA OF KING GEORGE ISLAND, ANTARCTICA

From the data of the pitting, geoelectrical prospecting, temperature measurement, salt content analysis and detection by layering frost-heaving instruments, the authors discuss firstly the structural features of sediments in the active layers in this region, and proves the presence of the bowl-shaped frost table in the stone-circles area, and then analyse the regulatities of temperature distribution in the active layer, effect of salt content on electric resistivity, thaw-settlement and frost-heaving, and their control on periglacial landform development. It suggests that the five layers should exist in the subsurface structure, namely, active layer, frost sand and gravel layer, frost volcanic rock permeated by sea water, frost volcanic rock unpermeated by sea water, and unfrost ancient continental basement. Finally, the permafrost table and its vertical gradient are deduced.     

SPECTRAL SIGNATURE OF COUPLED FLOW IN THE REFREEZING ACTIVE LAYER,NORTHERN ALASKA

Soil temperature records obtained from the active layer above permafrost at a site in northern Alaska during autumn and winter have variance spectra inconsistent with a purely conductive heat-transfer system. Although conductive heat-transfer theory predicts that temperature fluctuations are attenuated with depth, sub-diurnal thermal variance at the 50-cm level, near the base of the active layer, exceeded that at the 10-cm level. Short segments of the temperature record were drawn from three distinct periods of soil-frost conditions: (1) at the maximum vertical development of the active layer in early autumn; (2) during frost penetration and the formation of a zero curtain in early winter; and (3) after freezeback of the active layer. The variance spectra of these time series show systematic seasonal transitions that reflect changing mechanisms of heat transfer. During the first and second periods, heat transfer by internal evaporation and condensation dominates at wavelengths in the diurnal range. The spectral traces are not strongly self-similar and the fractal dimensions indicate extreme space-filling, especially at deeper levels. Once the active layer is frozen, conductive heat transfer dominates, producing a trend toward self-similarity. Both the thermal variance and the fractal dimension decrease with depth in the frozen regime. [Key words: Alaska, active layer, coupled flow, fractal dimension, frozen ground, heat transfer, permafrost, soil freezing, spectral analysis, zero curtain.]     

THE EFFECT OF SYNOPTIC SCALE WEATHER SYSTEMS ON SUB‐SURFACE SOIL TEMPERATURES IN A DIURNAL FROST ENVIRONMENT: PRELIMINARY OBSERVATIONS FROM SUB‐ANTARCTIC MARION ISLAND

Marion Island in the South Indian Ocean has a maritime climate dominated by diurnal frost processes in the landscape. We test the hypothesis that synoptic time‐scale measurements are essential in understanding the drivers of diurnal frost processes. Preliminary results from automated microclimate measurements in a polar desert habitat show that diurnal soil surface temperatures on Marion Island are influenced by a complex interaction of radiation balance, air mass circulation, cloud cover and snow. The passage of synoptic scale weather systems influences soil thermal characteristics through changes in dominance of the radiation budget. Soil frost on Marion appears to be dependent on clear skies, while synoptic weather systems affect the duration and intensity of soil frost processes and non‐radiative heat fluxes. Air circulation patterns at Marion Island influence diurnal scale temperature fluctuations and its direct and indirect interactions with ecosystem processes. The data suggest that in a maritime sub‐Antarctic environment the climatic drivers of soil frost occur at a finertemporal resolution than for seasonal and permafrost environments and needs to be measured at a diurnal time‐scale to be meaningful.     

长江源区五道梁的土壤热状况研究

活动层土壤热状况是寒区陆面物理过程研究的重要内容之一。利用五道梁能量收支观测站1993年9月～2000年12月份实测辐射及土壤热通量资料结合五道梁气象站1961-2010时段的气象资料分析了近50 a来该地区活动层土壤的热状况。结果表明：五道梁地区土壤热通量有显著的年际、年代际变化;20世纪60～80年代,土壤热通量小于0.0 W/m²,活动层土壤以放热为主,自90年代以来,土壤热通量大于0.0 W/m²,活动层土壤以吸热为主。过去50 a中该地土壤热通量呈现增大趋势,平均每10 a土壤热通量增大0.31 W/m²。土壤热通量随净辐射的增大而增大。土壤热平衡系数的变化特点与土壤热通量的变化特点一致。60～80年代,活动层土壤热平衡系数<1,该地区冻土相对比较稳定,而自90年代以来此间土壤热平衡系数<1,表明该地多年冻土呈现出退化迹象。活动层土壤热平衡系数可表示为气温、地表温度及水汽压的函数。     

Frozen Ground Phenomena in the Vicinity of Terra Nova Bay, Northern Victoria land, Antarctica: A Preliminary Report

Frozen ground phenomena in the Northern Foothills, Northern Victoria Land, Antarctica, include large–scale polygons, 15–20 m in diameter, and small frost mounds, 1–5 m high. The polygons are most widespread on terrain formed upon Younger Drift and are usually surrounded by interpolygon furrows or troughs, 10–30 cm deep and 10–100 cm wide. The troughs contain shallow wedges of sandy gravel (sand wedges) near the surface but excavations into underlying permafrost indicate that small ice wedges or ice veins are locally present. Field and anecdotal evidence suggest that thermal contraction cracking is active under today's climate. Frost mounds occur in association with a number of perennially frozen lakes in the region. In most cases they appear related to frost and icing blister activity caused by the episodic injection of free water from below. The debris–covered nature of the centre of Enigma Lake is best explained in terms of basal ice accretion beneath the lake–ice cover.     

2000—2015年中蒙俄经济走廊东段冻土时空变化及植被响应

中蒙俄经济走廊东段位于欧亚大陆多年冻土区东南缘及森林线南界接近区,冻土及生态环境脆弱。本文基于MERRA-Land陆面模式离线运行产品分析了中蒙俄经济走廊东段2000—2015年间冻土冻融的时空变化模式,以及冻土变化对返青期和全年不同阶段植被生长状态的影响。研究表明：2000—2015年间研究区多年冻土及季节冻土均持续退化,时间上主要表现为冻土提前解冻、延迟冻结;空间上主要表现为多年冻土南界的多年冻土退化和季节冻土下限抬升,及连续多年冻土南界的活动层加厚。解冻始日是森林地区植被返青的主控要素,林下冻土解冻对土壤含水量的增加及沼泽湿地的隔热蓄水功能影响了森林地区植被的生长。但随着多年冻土南界森林及林下泥炭地演替为草甸和农田,多年冻土退化,进一步促进林下沼泽湿地的消失。探讨冻土退化与生态环境之间的协同关系,有助于识别气候变暖和人类活动叠加影响下的冻土退化脆弱区以及生态环境敏感区。     

Freeze-thaw processes of active-layer soils in the Nanweng'he River National Natural Reserve in the Da Xing'anling Mountains,northern Northeast China

The active-layer soils overlying the permafrost are the most thermodynamically active zone of rock or soil and play important roles in the earth-atmosphere energy system. The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variation in mean annual temperatures and the formation of ground ice in permafrost regions. Using soil-temperature and-moisture data obtained from the active layer between September 2011 and October 2014 in the permafrost region of the Nanweng'he River in the Da Xing'anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Based on analysis of ground-temperature variation and hydrothermal transport characteristics, the thawing and freezing processes of the active layer were divided into three stages:(1) autumn-winter freezing,(2) winter freeze-up, and(3) spring-summer thawing. Variations in the soil temperature and moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freeze-thaw are discussed in this paper. The study's results show that thawing in the active layer was unidirectional, while the ground freezing was bidirectional(upward from the bottom of the active layer and downward from the ground surface).During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during a freezing-thawing cycle, the soil-water molecules migrate downward, i.e., soil moisture transports from the entire active layer to the upper limit of the permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil-moisture content and vegetation.     

Case studies: Frozen ground design and construction in Kotzebue, Alaska

Alaska has many construction design challenges due to permafrost. Due to either climate changes or human activities and development, permafrost often becomes unstable. Unstable soils can cause thaw settlement, frost jacking, or heaving. These can cause damage to infrastructure, increase maintenance costs, and decrease the life of construction projects. Kotzebue, Alaska, a remote village in the northwest arctic part of Alaska, is ideal for observing such permafrost effects on infrastructure. Three case studies of Kotzebue construction projects are reviewed here： the Front Loop Water Main Extension, which shows the importance of both passive and active freeze thaw protection for water service pipes and how to minimize differential movement between pipes and buildings; the Wastewater Lift Station Replacement, which describes methods for reducing thaw settlement in buildings over time when it is not feasible to prevent thaw settlement, and compares the benefits of frozen ground excavation over traditional excavation practices; and the Ted Stevens Way Rehabilitation, which discusses the effectiveness of 2001 best design practices for gravel road construction over tundra and permafrost, identifies their design and construction failures, and proposes future solutions.     

RECONNAISSANCE SURVEYS OF CONTEMPORARY PERMAFROST ENVIRONMENTS IN CENTRAL ICELAND USING GEOELECTRICAL METHODS: IMPLICATIONS FOR PERMAFROST DEGRADATION AND SEDIMENT FLUXES

Four different sites in the highlands of central Iceland have been investigated for permafrost occurrence using two‐dimensional resistivity imaging. The results of the surveys indicate the presence of shallow permafrost of low to medium resistivity. The distribution pattern is spatially heterogeneous which is consistent with permafrost at the fringe of seasonal frost. These sites are likely to react rapidly to changes of the environmental boundary conditions, therefore future research should include monitoring for detecting the early impact of climate change on permafrost degradation. The extent to which periglacial morphodynamics and sediment fluxes are influenced by permafrost and/or seasonal frost and potential permafrost degradation is hard to determine. Hence, long‐term monitoring approaches for both permafrost and sediment dynamics are essential.     

A full-scale field experiment to study the thermal-deformation process of widening highway embankments in permafrost regions

As one of the widely used upgrading way in road engineering, the widening embankment(WE) has suffered evident differential deformation, which is even severer for highway in permafrost regions due to the temperature sensitivity of frozen soil and the heat absorption effect of the asphalt pavement. Given this issue, a full-scale experimental highway of WE was performed along the Qinghai-Tibet Highway(QTH) to investigate the differential deformation features and its developing law. The continuous three years' monitoring data taken from the experimental site, including the ground temperature and the layered deformation of WE and original embankment(OE), were used to analyze the thermal-deformation process. The results indicate that the widening part presented the remarkable thermal disturbance to the existing embankment(EE). The underlying permafrost was in a noteworthy degradation state, embodying the apparent decrease of the permafrost table and the increase of the ground temperature. Correspondingly, the heat disruption induced by widening led to a much higher deformation at the widening side compared to the original embankment, showing a periodic stepwise curve. Specifically, the deformation mainly occurred in the junction of the EE and the widening part, most of which was caused by the thawing consolidation near the original permafrost table. In contrast, the deformation of EE mainly attributed to the compression of the active layer. Furthermore, it was the deformation origination differences that resulted in the differential deformation of WE developed gradually during the monitoring period, the maximum of which reached up to 64 mm.     

Study on the technology for highway construction and engineering practices in permafrost regions

In order to systemically summarize and integrate technology of highway construction in permafrost regions on the Qinghai-Tibet Plateau,we studied disciplines and mechanisms of formation and development of problems and challenges in highway engineer-ing in high-altitude permafrost regions based on construction experiences for 50 years and on 30 years of research regarding the Qinghai-Tibet and Xikang highways.Embankments,pavements,bridges,and countermeasures for ecosystem protection in per-mafrost regions were the main study objects.We combined extensive analysis of key problems of engineering stability with inter-action between permafrost and highways,theoretical models,indoor tests,and field tests to reveal the interaction between em-bankments,pavements,bridge piles,and permafrost.In this paper,we propose a series of engineering measures for highway sta-bility,design parameters,key indexes for pavement durability in low temperature,relationships between re-freezing time of bridge-pile foundation and strength development as well as ecosystem recovery in high-latitude cold regions;these eventually form a construction technology package for permafrost regions.     

Problems and countermeasures in construction of transmission line projects in permafrost regions

Construction of power transmission lines is becoming an important part of permafrost engineering in China.This paper reviews the construction status and problems of transmission lines in different countries,as well as corresponding solutions that would be of practical significance for sustainable engineering practices.Russia has the longest history of transmission line construction in permafrost areas,with transmission lines（mainly 220 kV and 500 kV） spanning approximately 100,000 km.However,all countries suffer from permafrost-related tower foundation stability problems caused by freezing-thawing hazards such as frost heave and thaw settlement,frost lifting,and harmful cryogenic phenomena.As point-line transmission line constructions,the lines,poles and towers should be reasonably selected and installed with a comprehensive consideration of frozen soil characteristics to effectively reduce the occurrence of freezing-thawing disasters.Reinforced concrete pile foundations are widely used in the permafrost regions,and construction in winter is also a universal practice.Moreover,facilitating engineering measures like thermosyphons are an effective way to reduce freezing-thawing hazards and to maintain the stability of tower foundations.