Permafrost Characteristics of the Qinghai-Tibet Plateau and Methods of Roadbed Construction of Railway

Permafrost along the Qinghai-Tibet railway is featured by abundant ground ice and high ground temperature. Under the influence of climate warming and engineering activities, the permafrost is under degradation process. The main difficulty in railway roadbed construction is how to prevent thawing settlement caused by degradation of permafrost. Therefore the proactively cooling methods based on controlling solar radiation, heat conductivity and heat convection were adopted instead of the traditional passive methods, which is simply increasing thermal resistance. The cooling methods used in the Qinghai-Tibet railway construction include sunshine-shielding roadbeds, crushed rock based roadbeds, roadbeds with rock revetments, duct-ventilated roadbeds, thermosyphon installed roadbeds and land bridges. The field monitored data show that the cooling methods are effective in protecting the underlying permafrost, the permafrost table was uplifted under the embankments and therefore the roadbed stability was guaranteed.     

青藏工程走廊典型热融灾害现象及其热影响研究

在全球变暖及人类工程活动的影响下,青藏工程走廊内的热融灾害普遍发育。研究走廊内各类热融灾害的发育现状及其对多年冻土的热影响对今后的工程规划和冻土环境保护具有一定的指导意义。本文通过大量的野外调查工作,总结了走廊内热融灾害的类型及其发育现状,并选取3种典型热融灾害进行现场地温监测,分析其对多年冻土的热影响方式和程度。研究结果表明:3种热融灾害对其发育区域及附近的多年冻土都产生了巨大的热影响,热融滑塌和热融沟主要影响浅层的地温状况,而热融湖塘的影响范围更大,其发育甚至会导致湖塘下部形成多年融区。此外,侧向热流计算结果表明,3种热融灾害全年都在向其周边的多年冻土放热,通过对比发现热融湖塘的侧向热侵蚀能力最强,其次是热融沟,侧向热侵蚀最小的是热融滑塌。     

大兴安岭北部多年冻土地区路基沉陷研究

通过对该区４个路段１２个断面为期３ａ的路基沉陷观测并结合线路普查和分析表明,多年冻土路基稳定性与地基的水、热状况密切相关,受自然环境和人为因素的制约。合理布线、保护植被、改善排水、合理确定路基高度以及设置护坡、基底反铺塔头、采用土工聚合材料和无基管涵结构等,是保持该地区路基稳定的有效措施。     

Permafrost warming under the earthen roadbed of the Qinghai–Tibet Railway

This paper investigates the stability of the earthen roadbed built in the warm and ice-rich permafrost region. The varying thermal regime of the subgrade and the ongoing settlement of the roadbed were observed at field. The temperature data demonstrate that in warm and ice-rich permafrost regions, adoption of earthen roadbed results in warming of the underlying permafrost. It is primarily because the earthen roadbed traps the warm-season absorbed heat in the natural ground. In addition, the carried heat of the earthen roadbed that was constructed in warm season propagates downward to warm the underlying soil. The warming permafrost layer promotes the roadbed settlement, which was mostly linearly developed in the past five service years. A comprehensive analysis for the varying thermal regime and the ongoing settlement shows that the unfrozen water liberated from the warming, undrained layer experiences consolidation. The deformation of the undrained soils is mainly responsible for settlement of the roadbed. In comparison, the temperature variation of this warming permafrost layer is found to be less beneath roadbeds protected by thermosyphons or crushed rock revetments. The installation of thermosyphons into the earthen roadbed is recommended to prevent the further degradation of the underlying permafrost.     

青藏铁路碎石护坡-热管复合措施的补强效果研究

青藏铁路高温冻土区的普通路基和保温材料路基均处于热不稳定状态, 需要对它们增设碎石护坡-热管复合措施来强化处理, 新增设的补强措施对路基下部冻土的保护效果如何是人们极为关心的问题. 因此, 对北麓河高温高含冰量路段增设了碎石护坡及热管的复合补强措施后路基下部土体的热状态进行观测.结果显示:普通路基在增设补强措施后, 人为冻土上限进一步抬升, 阴阳坡下均出现显著的降温趋势, 且路基下温度场逐渐趋于对称, 降温范围逐渐向路基中心及深部发展, 路堤中心深部地温仍处于增温状态, 但增温趋势明显缓减; 保温材料路基在增设补强措施后, 人为冻土上限也进一步的抬升至保温板附近, 融化夹层在2个冻融周期后消失, 路堤中心温度在2个冻融周期后出现了降温趋势. 这些效果说明, 补强措施在调控路基内部及下部多年冻土温度时发挥了积极作用.     

The effect of permafrost changes on embankment stability along the Qinghai–Xizang Railway

After construction of the Qinghai–Xizang Railway, the resultant heat exchange between soil and atmosphere caused changes in the thermal and mechanical stability of permafrost beneath the railway embankment. Monitoring from 2005 to 2010 indicated 12 sections of embankment that experienced more than 5 cm of settlement, with three showing deformations of more than 10 cm and signs of continuing settlement. Embankment stability is closely related to permafrost changes beneath the embankment. Large-scale deformations have contributed to permafrost thaw and artificial permafrost table deepening, and this deformation has not stabilized over the short term. In contrast, small-scale deformations have contributed to a warming of the permafrost that has gradually stabilized as soil temperature decreases. Only three sections of the Qinghai–Xizang Railway have exhibited settlement deformation that exceeds 10 cm, through a deepening of the artificial permafrost table and a gradual increase in permafrost thawing result in embankment settlement deformation. However, with climate warming trends and the long-term operation of the railway, the long-term thermal and mechanical stability of the embankment needs to be carefully monitored to ensure the safe operation of the Qinghai–Xizang Railway.     

基于热稳定性的冻土区铁路路基过渡段结构改进研究

自青藏铁路通车以来,其冻土地区铁路路基的融沉冻胀病害层出不穷,铁路路基过渡段的差异沉降问题尤为严重。基于一般地区铁路路基过渡段差异沉降的治理方法,结合冻土区铁路路基的主动降温措施,对冻土区铁路路基过渡段施工结构进行了探索性的改进研究,并对改进后铁路路基过渡段的长期热稳定性进行了分析。结果表明：将传统块碎石铁路路基上层路基填料换填成一定高度的单一粒径碎石,可使铁路路基在满足力学稳定性的前提下,实现最大限度的自然对流换热效应;通过数值模拟计算分析发现,改进后的铁路路基过渡段结构在气温变暖的环境背景下主动降温效果明显,且长期热稳定性好;桥台对铁路路基过渡段的温度场影响较大,建议对受太阳辐射强烈的桥台进行保温处理。     

青藏铁路冻土路基变形监测与分析

基于现场监测资料,对作为青藏铁路中的主要保护冻土的几种路基形式（如：通风管路基、块石路基、块石护坡路基、保温材料路基和普通素土路基）进行了变形和温度分析,发现所有路基的变形均以沉降变形为主,且其变形与其下伏冻土的地温场变化密切相关。经过2～3个冻融周期后,通风管路基、块石路基、块石护坡路基和保温材料路基的变形已趋于稳定,而无任何措施的普通路基目前变形仍未稳定。另外,各种路基左右路肩均存在变形差。基于以上分析可得到一个启示：在高温、高含冰量冻土地区,由于路基下多年冻土温度升高产生的高温冻土压缩变形而引起的路基沉降变形具有相当大的量级,很有可能成为冻土路基发生破坏的一个重要原因,工程实践中应给予足够的重视。     

青藏高原多年冻土区碎石护坡降温作用及效果分析

基于青藏高原北麓河多年冻土区碎石护坡路基与普通路基温度监测资料分析,结果表明:碎石层的铺设具有减小坡面年平均温度及坡面温度年较差的作用;与普通路基相比,碎石护坡在暖季主要起到隔热作用,但在冷季主要存在不利于路基散热的弊病.从路基人为冻土上限抬升状况、温度降低程度和路基变形量的差异来看,碎石护坡路基较普通路基有利于冻土路基的热稳定性.但碎石护坡调节路基内部温度场是一个长期过程,即坡面温度对多年冻土温度的影响具有滞后性,若作为青藏铁路多年冻土区补强措施使用时应慎重.     

青藏铁路多年冻土区路基变形裂缝发生机理及其防治

青藏铁路多年冻土区路基工程的修建,改变了路基基底多年冻土的热量平衡状态.通过对青藏铁路多年冻土区试验工程和已经施工的路基工程所发生的变形裂缝的调查和分析,认为多年冻土区路基几何尺寸不对称和路基边坡坡向不同导致的路基人为上限形态不同,是造成多年冻土区路基温度场不对称以及基底土体冻结融化过程不同步的主要原因,也是造成路基变形裂缝的主要原因.文章在此基础上提出了减少或消除路基温度场不对称,从而减少或消除这类变形裂缝的主要工程结构形式和工程措施,作者的看法和结论已经在2003年青藏铁路冻土区路基工程设计和成形路基补强工程措施设计中得到广泛应用.     

青藏铁路冻土区路桥过渡段沉降原因分析

青藏铁路开通近10 a以来,各类冻土工程稳定,保证了列车平稳安全的运行。然而,青藏铁路工程也不可避免出现了一些病害问题。现场调查资料表明,冻土区路桥过渡段下沉现象较为严重。通过冻土区路桥过渡段的沉降特点和工程地质条件综合分析,结果表明：地表水或冻结层上水水热侵蚀,引起人为多年冻土上限下降、高含冰量冻土层融化,致使路基发生强烈的融化下沉。建议这类工程病害应采取主动降温措施增强地基土的冻结能力,并加强防排水设施和改善地表水条件,消除水热侵蚀所产生的融化下沉。研究结果为青藏铁路路桥过渡段的稳定性和养护提供了科学依据。     

青藏高原多年冻土地区公路路基变形

通过对现场实体工程的长期监测资料和路基破坏机理分析研究,使我们对沥青路面对多年冻土的严重影响,导致多年冻土的升温与退化,使路基产生较严重的不均匀下沉变形,及其它所引起的一系列路基病害问题的发生发展过程有了较为系统和深刻认识,取得了大量现场实测资料及研究成果.讨论了高温多年冻土地区冻土路基的变形特征,以及冻土路基变形与工程地质条件的关系,给出了路基随地温波动变化而发生的变形过程。     

Study on the Reasonable Height of Embankment in Qinghai–Tibet Highway

A reasonable height of embankment is beneficial for maintaining the thermal and mechanical stability of highway in cold regions. This paper firstly introduced theoretical models for two main sources of settlement, including an improved consolidation theory for thawing permafrost and a simple rheological element based creep model for warm frozen soils. A modified numerical method for living calculating thaw consolidation and creep in corresponding domains and for post-processing the proportion of each source in total settlement based on the effective thaw consolidation time. Two typical geological sections underlain by warm permafrost layer were selected from the Qinghai–Tibet highway. The heat transfer and continuing settlement for two sections were modeled by assuming that the height of embankment ranges from 0 to 6.0 m. The reasonable critical height for two sections are 1.63 and 1.35 m, respectively, by comparing maximum thawing depth, mean annual temperature and settlement in the roadbed center. For two sections with design height of embankment, the proportions of thaw consolidation and creep to the total settlement were analyzed. For sections at higher ground temperature, thaw consolidation accounts for a major part while thaw consolidation of section L is a little larger than that of creep.     

Thermal hazards zonation and permafrost change over the Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau is the largest permafrost region at low latitude in the world. Climate warming may lead to permafrost temperature rise, ground ice thawing and permafrost degradation, thus inducing thermal hazards. In this paper, the ARCGIS method is used to calculate the changes of ground ice content and active layer thickness under different climate scenarios on the Qinghai–Tibet Plateau, in the coming decades, thus providing the basis for hazards zonation. The method proposed by Nelson in 2002 was used for hazards zonation after revision, which was based on the changes of active layer thickness and ground ice content. The study shows that permafrost exhibits different degrees of degradation in the different climate scenarios. The thawing of ground ice and the change from low-temperature to high-temperature permafrost were the main permafrost degradation modes. This process, accompanied with thinning permafrost, increases the active layer thickness and the northward movement of the permafrost southern boundary. By 2099, the permafrost area decreases by 46.2, 16.01 and 8.5% under scenarios A2, A1B and B1, respectively. The greatest danger zones are located mainly to the south of the West Kunlun Mountains, the middle of the Qingnan Valley, the southern piedmont of the Gangdise and Nyainqentanglha Mountains and some regions in the southern piedmont of the Himalayas. The Qinghai–Tibet Plateau permafrost region is in the low-risk category. Climate warming exacerbates the development of thermal hazards. In 2099, the permafrost region is mainly in the middle-risk category, and only a small portion is in the low-risk category.     

青藏铁路多年冻土区路基变形特征及其来源

基于青藏铁路多年冻土区34个路基监测断面2005－2011年的变形与地温资料,分析路基的变形特征及其来源。监测结果表明：①监测期累计变形量大于100 mm的断面均为普通路基,其变形主要来自路基下部因冻土上限下降而引起的高含冰量冻土的融沉变形以及融土的压密变形,其次为路基下部多年冻土因地温升高而产生的高温冻土的压缩变形。②监测期累计变形量小于100 mm的普通路基与块石结构路基断面,其变形主要来自路基下部多年冻土的压缩变形。③总体而言,块石结构路基变形量明显小于普通路基,从而验证了主动冷却措施的长期有效性。其研究结果可为冻土区路基稳定性判断及病害预警提供数据支持。     

Interactions between freeze–thaw actions,wind erosion desertification,and permafrost in the Qinghai–Tibet Plateau

The unique natural environment of the Qinghai–Tibet Plateau has led to the development of widespread permafrost and desertification. However, the relationship between desertification and permafrost is rarely explored. Here we study the interaction between desertification and permafrost using a combination of simulations, experiments, and field observations in the Qinghai–Tibet Plateau. Results show the cohesion values of the test samples that experienced 1, 3, and 6 freeze–thaw cycle times decreased by 65.9, 46.0, and 35.5 %, respectively, and the compressive strength of the test samples decreased by 69.6, 39.6, and 34.7 %, respectively, compared to the test samples that did not experience freeze–thaw cycles. The wind erosion rate of the test block eroded by sand-bearing wind was far larger than that by clean wind under the same conditions; the maximum value was 50 times higher than that by clean wind. The wind erosion rate increased with an increasing number of freeze–thaw cycles, water content, and freeze–thaw temperature difference. The ground temperature below the sand layer was decreased, compared to the natural ground surface that without sand layer covering, the drop amplitude of yearly average temperature was roughly maintained at 0.2 °C below the thick sand layer (1.2 m), and the maximum drop of yearly average temperature was 0.7 °C below the thin sand layer (0.1 m). Therefore, with the presence of water, the destruction of surface soil structure caused by repeated and fierce freeze–thaw actions is the main cause of wind erosion desertification in the permafrost region of Qinghai–Tibet Plateau, and sand-bearing wind is the main dynamic force. The development of eolian sand deposits after the desertification emerges. As a result, the properties of the underlying surface are altered. Due to the high reflectivity and poor heat conductivity of the sand layer, the heat exchange of the land–atmosphere system is impeded, causing a drop in the ground temperature of the underlying permafrost that subsequently preserves the permafrost.     

青藏公路路基变形分析

为研究青藏公路多年冻土人为上限在退化过程中对路基变形产生的影响过程和程度, 在唐古拉山以南选择了3处具有代表性的路面进行了为期2 a的路面变形观测. 资料表明, 在多年冻土人为上限退化过程中随着公路路基结构、冻土类型的不同, 路基变形从冻胀和融沉过程、冻胀量和融沉量、发生的时间都有很大的不同. 在高含冰量多年冻土区采用半挖半填结构产生的路基变形最为剧烈, 在含冰量相对少且采用较高路堤结构的地段路基变形过程相对平缓. 同时结合探地雷达的勘察结果对路基下的融化区、多年冻土区的内部结构进行了分析. 结果显示,多年冻土人为上限的下移、地下冰的融化会在多年冻土人为上限以上的地质体中导致较强烈的层间错动和扰动.     

大兴安岭北部霍拉河盆地季节融化层的研究

大兴安岭北部霍拉河盆地季节融化层的特征受气温的控制,并随地面条件、含水量和土质的不同而变化。最大季节融化深度,在土类相同时,裸露的比有植被和雪盖的深0.4—0.5m;土类不同时,卵砾石的最大,碎石亚粘土、亚粘土和草炭亚粘土的分别为卵砾石的0.65、0.5和0.4倍。年平均地温为-0.1℃的季节融化层比年平均地温为0——0.5℃的约提前2—3个月消失。回冻融化层中的地下冰与青藏高原相比,不甚发育,冻土构造主要呈整体状、微层状和裂隙状。     

青藏铁路冻土区块石护坡路基热传递特性

块石护坡路基是青藏铁路建设中一种有效的冷却地基保护冻土工程措施.考虑高原夏季夜间冷空气对块石护坡路基温度场的影响,对青藏铁路北麓河块石护坡试验路基夏季某一整天的温度场、热流量和热流密度进行了分析,研究块石护坡路基昼夜间热传递特性.结果表明:块石护坡路基在夏季白天吸收热量,在夜间冷空气的作用下路基释放一部分热量,说明夏季夜间存在一定的降温效果.另外考虑一年内冷暖季块石护坡的热传递差异,对块石护坡路基冷暖季的温度场、热流量和热流密度变化情况进行研究,探讨其冷暖季热传递特性,结果显示:块石护坡路基暖季处于吸热状态,冷季处于放热状态;从一年的热流量变化看,块石护坡路基冷季的放热量大于吸热量,路基储存冷能有利于保护冻土.     

青藏公路沿线热喀斯特湖分布特征及其热效应研究

热喀斯特湖的出现和发育是多年冻土变暖的指示器,研究热喀斯特湖发育及其热效应是应对青藏高原气候变化和人类活动诱发冻土灾害的基础工作.基于SPOT-5卫星影像资料,在ArcGIS平台下解译遥感影像,获取了青藏公路沿线楚玛尔河至风火山段热喀斯特湖的数量和分布特征,这些热喀斯特湖以楚玛尔河高平原和北麓河盆地为主要分布区,且80％发育于高含冰量多年冻土区.热喀斯特湖通过竖向和侧向2种传热方式影响多年冻土,竖向传热会造成其下部多年冻土融穿,侧向传热会造成湖岸多年冻土增温,扩大热影响范围.通过北麓河地区一典型热喀斯特湖的数值计算,湖全年都在向湖岸放热.当热喀斯特湖离路基较近,将会对公路产生潜在或者直接的危害,其侧向热侵蚀往往会导致冻土路基温度升高,诱发路基病害.