试论青藏高原多年冻土类型的划分

本文采用综合分析与主导因素相结合的原则，以干燥度作为主要指标并参考年降水量，年平均相对湿度及气温较差等，结合地形因素将青藏庙的多年冻土划分为：湿润，亚湿润，半干旱，干旱和极干旱５种类型，并对各类型代表性和冻土地区进行分别论述。     

气候变化对中国多年冻土和寒区环境的影响

中国的多年冻土总面积为 2 .1 5× 1 0 6 km2 ,主要分布在高海拔地区。 40年来 ,随寒区经济的快速发展和资源、环境问题的日益突出 ,冻土和寒区气候变化研究获得了长足的进展。我国大部分地区的多年冻土退缩趋势明显。 2 1世纪 ,受气候变暖和人为活动的共同影响 ,青藏高原和东北地区北部多年冻土将大幅退缩。冻土广泛退缩将对中国的寒区经济和环境产生重要影响。但是 ,冻土退缩及其对环境的影响还存在很大的不确定性。     

新藏公路新疆段多年冻土特征及其灾害初探

新藏公路新疆段沿线海拔高，气候干冷，第四纪松散堆积层厚，在高山区和山原河谷盆地区发育了多年冻土。勘查研究表明：多年冻土分布于K306 000～K310 000和K515 000～K705 00间191．6km路段上，属高原片状连续多年冻土。沿线个别路段含冰量较高，为多冰-富冰冻土，中冻胀中融沉；绝大部分路段以少冰多年冻土为主，弱冻胀弱融沉。现有公路主要冻土灾害有涎流冰、路基融沉、路面翻浆、冻胀破坏、冻融滑塌和冻融泥流等。随着整治改建工程的实施，多年冻土原有的水热平衡的破坏，冻土灾害将趋于严重。根据沿线多年冻土的特征，提出施工和运营中应采取保护冻土的设计原则，通过改线避绕、抬高路基、提高路基强度及完善截排水系统等5条措施以减少公路工程对多年冻土的扰动和破坏。     

积雪对冻土热状况的影响

研究表明季节性积雪对其下覆冻土的热状况有显著的影响，雪盖的存在不仅阻隔了冻土层的热能散失，从而有提高地温的作用；而且由于积雪本身所具有的低导热性和较大容积热容量等特点，延滞外部气候条件对冻土热状况的影响。反映冻土热状况的一个重要指标－冻土深度的变化与气温，太阳辐射的变化密切相关，因此，地理位置和地形在地一气系统之间的能量交换中，对冻土的状况也重要的影响作用。     

黄河源区冻土分布制图及其热稳定性特征模拟

以黄河源区多年冻土分布现状和热力特征为研究目标,通过野外调查及实测数据,分析了黄河源区不同地形地貌、不同地表覆盖条件下的冻土形成、分布特征和以地温为基础的热学特征,探讨了不同尺度因素对多年冻土分布的影响。结果表明,在高程低于4 300 m的平原区,多年冻土多不发育;在高于4 350 m的山区,局地地形对多年冻土的形成与分布作用显著。除阳坡地形外,多年冻土均比较发育;介于4 300~4 350 m的低山丘陵和平原区,局地地形、地表植被、土壤湿度等因素共同决定着多年冻土的形成和分布格局。以年均地温指标为基础,构建了以纬度、经度和高程为自变量的回归模型,并对阳坡地形进行微调和校正。结果表明,以0oC作为划分季节冻土和多年冻土的标准和界限,多年冻土面积2.5×10⁴km²,约占整个源区面积的85.1%;季节冻土面积0.3×10⁴km²,约占整个源区面积的9.7%。进一步以0.5oC或1.0oC为分类间隔绘制了黄河源区多年冻土热稳定性空间分布图。     

黄河源区多年冻土温度及厚度研究新进展

利用新布设的冻土孔及原有冻土资料,分析黄河源区冻土温度和厚度的空间分布。源区实测多年冻土年均地温最低为-1.81℃,冻土最厚74 m,均位于巴颜喀拉山北坡的查拉坪。214国道(K445-K604段)沿线多为高温多年冻土(年均地温>-1℃),但巴山北坡海拔4 520 m、布青山海拔4 300 m以上,年均地温低于-0.5℃。巴山北坡海拔4 610 m、布青山海拔4 420 m以上,年均地温低于-1℃。巴山北坡海拔每升高100 m,年均地温减少0.47~0.75℃,冻土厚度增加16~25 m;纬度向北增加1°,年均地温减少0.85℃,冻土厚度增加20~30 m。     

青藏高原西部区域多年冻土分布模拟及其下限估算

准确评估青藏高原西部多年冻土的空间分布及多年冻土下限深度情况对该区地下水资源利用、生态环境保护有重要意义.本文依托科技基础性工作专项“青藏高原多年冻土本底调查”在该区及周边取得的冻土调查资料,利用遥感数据和扩展地面冻结数模型模拟了该区多年冻土的空间分布,调查区的模拟验证表明该方法有较高的精度.在此基础上,根据有限的地温实测资料建立了地温与位置、高程、坡向和太阳辐射的关系,并根据地温-下限关系估算了该区多年冻土下限深度的分布情况.研究表明,该区有多年冻土约占36.9%,季节冻土占57.5%,多年冻土主要分布在34°N~36.5°N范围的喀喇昆仑、西昆仑一带,季节冻土主要分布在塔里木盆地和34°N以南地区.阿里高原及以南是岛状多年冻土分布区域,其多年冻土分布面积少于此前出版的冻土图所绘制的.青藏高原西部区域的多年冻土下限深度整体表现为由东南-西北逐渐加深.     

基于COUPMODEL模型的冻融土壤水热耦合模拟研究

利用COUPMODEL模型,对唐古拉研究区活动层土壤的水热特征进行模拟,与观测结果进行对比发现,在活动层土壤温度方面,COUPMODEL模型的模拟结果R2>0.94,其平均值为0.98,均方根误差较小,模拟效果较理想;在活动层水分特征方面,模拟结果存在一定偏差,R2介于0.88~0.93之间,平均值0.90,均方根误差平均值4.24,基本反映了高海拔多年冻土区活动层水热变化;在土壤热通量方面,0~20 cm土壤热通量的模拟结果与观测值基本一致;模型模拟的冻结深度在3 m左右,接近观测值,COUPMODEL模型可用于多年冻土区活动层土壤水热变化规律研究。     

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.     

青藏高原工程走廊冻土分布模型及其变化趋势

青藏高原工程走廊多年冻土是地气系统相互作用的产物,气候环境决定了其分布的宏观格局,但局地因素如坡向等,在一定条件下,对小区域多年冻土的影响往往会超过大气候背景。通过Pearson相关性分析,选取了对青藏高原工程走廊多年冻土分布影响较大、在GIS技术支持下较容易量化的坡向,结合区域内29个钻孔点的长期地温监测数据,建立了年平均地温与高程、纬度及坡向之间的多元线性模型。根据青藏高原冻土工程地温分带指标,制作出了走廊内符合实际的冻土分布图。运用随气候变化的响应模型,预测了走廊内50 a后多年冻土将发生较大的变化:1.低温稳定区、低温基本稳定区的空间分布面积逐渐减小,分布界线向高海拔迁移;2.高温不稳定区较大范围地向高温极不稳定区转化;3.高温极不稳定区将处于长期的退化过程。     

青康公司（国道214线）沿线的多年冻土

青康公路沿线多年冻土主要分布于河卡南山,鄂拉山,巴颜喀拉山地及花石峡至至多间的低山区丘陵区,呈断续分布,总长共３３０ｋｍ。其分布特征主要受海拔高度控制,但又具有纬度地带性,局地因素同时也起作用。公路沿线冻土退化和冻土环境变化的迹象明显。     

Dynamic response of wind turbine towers in warm permafrost

Wind is a great source of renewable energy in western Alaska.Consistent winds blow across the barren tundra underlain by warm permafrost in the winter season,when the energy demand is the highest.Foundation engineering in warm permafrost has always been a challenge in wind energy development.Degrading warm permafrost poses engineering issues to design,construction,and operation of wind turbines.This paper describes the foundation design of a wind turbine built in western Alaska.It presents a system for response monitoring and load assessment,and data collected from September 2013 to March 2014.The dynamic properties are assessed based on the monitoring data,and seasonal changes in the dynamic properties of the turbine tower-foundation system and likely resonance between the spinning blades and the tower structure are discussed.These analyses of a wind turbine in warm permafrost are valuable for designing or retrofitting of foundations in warm permafrost.     

Qinghai-Tibet Expressway experimental research

As one part of the National Highway Network Planning in China, the Qinghai-Tibet Expressway （QTE） from Golmud to Lhasa will be built in the interior of the Qinghai-Tibet Plateau （QTP） across about 630 km of permafrost lands. Due to the problematic interactions between the engineering foundations and permafrost, the frozen-soil roadbed of the QTE will be subjected to the more intense thermal disturbances due to the wider black surface. The design and construction for long-term thermal and mechanical stability will face more severe challenges than those in ordinary highways and railways in the same region. In order to provide scientific support for cold regions engineering practices, the QTE Experimental Demonstration Project （EDP） was constructed in situ in the vicinity of the Beilu＇he Permafrost Station in the interior of the QTP. In this paper, the anticipated problems of the proposed QTE project are enumerated, and the structures of the test sections for QTE EDP are described. Through numerical simulations, it was found that the heat transfer processes occurring in each specific road structure are significantly different. The heat accumulation in the highway embankment is mainly due to the black bituminous pavement, but in the railway embankment with its gravel surfaces, it mainly comes from the side slopes. As a result, the net heat accumulation of the highway embankment is three times higher than that in the railway. In expressway, the heat accumulation is further increased because of the wider pavement so that significantly more heat will be accumulated in the roadbed beneath the centerline area. Thus, the thermal stability of the fro- zen-soil roadbed and the underlying permafrost of the QTE can be seriously threatened without proper engineering measures protection against thawing. Based on research and practical experiences from the operating Qinghai-Tibet Railway （QTR） and the Qinghai-Tibet Highway （QTH）, combined with the predicted characteristics of heat transfer in an expressway embankment, nine kinds of engineering measures for mitigating the thaw settlement of foundation soils through the cooling the roadbed soils were built and are being tested in the EDP. The design of the monitoring system for the EDP and the observed parameters were also described.     

Medium and small embankment dams on permafrost: A discussion of current concepts

This article discusses the current concepts of dam design and construction in permafrost regions. It is demonstrated that embankment dams often change their state from frozen to thawed and back during the operation period. It is shown that these transitions are not always attributable to observed climate warming. Where geotechnical, hydrogeological, and permafrost conditions are complicated, proper performance of embankment dams can only be provided by adhering to a selected thermal design for, as an example, a frozen state.     

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。     

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.