青藏铁路典型地段变形特征分析

冻土区路基变形问题的核心就是研究路基内地温的变化.通过分析青藏铁路典型地段气温地温均低、气温高地温低、气温地温均高3种不同地段在工程热扰动阶段、路基趋于稳定阶段、铁路长期运营阶段的地温变形原始资料,得到相应地段在不同时期的地温和变形特征.分析结果表明,气温、地温均高地段路基抵御未来气温升高的能量积累不足,产生的沉降变形量最大,因此必须采用相应的工程措施.     

Analysis of the Theoretical Foundation and Engineering Effect for Air-duct Embankment on the Qinghai-Tibet Railway

Based on the corresponding theories of engineering thermodynamics and hydro-dynamics, a careful study is made of the characteristics of air flow in different duct-embedded ways. According to critical Reynolds number, the atmospheric critical velocity of the duct with different diameters, which makes laminar flow different from turbulent flow, is calculated. Given the condition in which a forced flow occurs and the wind strength is larger than the atmospheric pressure gradient along the air-duct, a rational ratio of the length to the diameter is presented. Based on the above theory and field test data on soil temperature and embankment settlement, the advantages and disadvantages are discussed in details of all duct-embedded ways that might affect the stability of embankment.     

Numerical Analysis for Temperature Characteristics of Open Boundary Crushed-rock Embankment on Qinghai-Tibet Railway

At present, in order to protect the stability of permafrost beneath embankment, the crushed-rock embankment, as a new type of embankment structure, has widely been used in the construction of Qinghai- Tibet Railway. Its crushed-rock layer is almost open in tow bilateral boundaries and closed at top and bottom, and air can flow into/out of the ballast layer and crushed-rock layer. Therefore, the convection and transfer heat patterns are very complicated in the ballast layer and crushed-rock layer of the embankment, which are regarded as porous media. In this paper, based on the wind, temperature and geology conditions of Qinghai- Tibet Plateau, a numerical approach of the unsteady two-dimensional continuity, momentum （non-Darcy flow） and energy equations of heat convection for incompressible fluid in porous media is provide to analyse the velocity and temperature characteristics of the crushed-rock embankment with different embankment heights under open boundary condition for the coming 50 years. The calculated results indicate that, due to the influence of the external wind, the convective heat transfer mainly relies on the forced convection in the open crushed-rock emban kment. Even if the air temperature will be wanned up by 2.6℃ in the coming 50 years, it still has a better cooling effect on the underlying soils and a low temperature frozen-soil core is formed in the permafrost below it if the embankment is constructed in the regions whose present mean annual air temperature is - 4.0℃. Furthermore, the cooling effect of high crushed-rock embankment is better than that of low embankment. This results from the fact that the wider bottom of high emban kment has a more influence dimension on the underlying frozen soil. However, cardinal winds on Qinghai-Tibet Plateau disturb its convection pattern, so that an asymmetric temperature distribution occurs under high embankment and it is possible to induce a transverse uneven deformation of emban kment, but no similar situation occurs under low embankment. This asymmetric temperature field problem should be considered when crushed-rock emban kment is designed and constructed.     

青藏铁路运营期间冻土路基裂缝问题研究

运营期青藏铁路冻土区路基工程最值得关注的变化是不同部位裂缝的发生和发展以及对线路安全运行的影响.通过对不同时期青藏铁路多年冻土区路基工程裂缝发生发展影响因素的分析,认为冻土区路基工程基底地温场的不对称以及基底土体冻融过程不同步是路基工程变形裂缝发生的主要原因,路基坡脚和周围冻土水热环境变化是裂缝发展的拉动力,路基填料性质也是不容忽略的因素;根据运营期间冻土路基热状态和工程状态分析,对运营期青藏铁路冻土路基工程状态进行了初步评价,并提出了减少或消除地温场的不对称及保护路基坡脚冻土环境,从而抑制冻土路基裂缝的工程对策.     

Investigation and Analysis on New Harmful Features Related to Frozen Ground in Permafrost Regions in Qinghai-Tibet Railway

1Introduction Harmfulfeaturesrelatedtofrozengroundaredefinedassuchphysicalandgeographicalfeatures soilhas,whichareharmfultoengineering,triggeredbyfreezingandthawingeffects.Constructingarailwayonpermafrostwill encountermanyharmfulfeatures,andontheotherhand,therailwaybuiltwillgeneratemoreharmful feature,whichmyposeathreattotherailway.So theinvestigationandresearchofthetypes,distributionanddevelopmentcharacteristicsofthe mainsecondaryharmfulfeaturesalongQinghai TibetRailway,toofferguidancetodesi…     

青藏铁路低温冻土区片石路基的温度特征

在青藏铁路五道梁低温冻土区进行了片石护道路基新结构和土护道路基结构的实体工程试验,以确定路基修筑对温度场的影响.对测试断面冻融循环的地温监测资料的分析表明,2004年片石路基左右路肩孔冻土上限处,年平均地温分别低于土护道路基相应位置0.12℃和0.14℃,2005年片石路基左右路肩孔分别低于土护道路基相应位置0.65℃和0.03℃,冻土上限以下地温均呈逐年下降趋势.片石护道和土护道路基冻土上限均存在不对称性,但随着时间发展,片石护道路基最大融化深度位置基本接近或超过天然地面,且冷生过程还在继续.该区域的片石护道路基新结构能够有效发挥降低地温、主动保护多年冻土的作用.     

路基宽度对多年冻土区站场路基温度场的影响

青藏铁路路基的热稳定性受到气温升高的影响.站场路堤比普通路堤宽度大,受气温升高影响更大.以清水河站场试验点为工程背景,对站场和普通路基3个冻融周期的现场测试温度进行分析比较.参照前人对气温预测计算公式,作为青藏铁路站场路基进行热分析的边界条件,运用数值计算方法近似求解计算站场路基20 a后的热状况,同时与普通宽度的路基作比较.结果表明,站场路堤的多年冻土的人为上限比普通路堤高,最大融深比普通路堤大,说明路基的宽度是加速冻土破坏的一个重要影响因素.     

青藏铁路清水河地区路堤最小设计高度的计算

在青藏铁路多年冻土区路基的设计中,临界高度和最小设计高度是两个关键指标.本文针对青藏铁路清水河试验段特定条件下的试验路堤进行了研究,分析了路堤高度与上限上升高度的关系,并根据试验所得的路堤临界高度值,计算得到了该地区特定条件下路堤的最小设计高度值.研究表明:①青藏高原清水河地区铁路路堤存在临界高度;②清水河地区铁路路堤的临界高度为0.65 m;③清水河地区铁路路堤的最小设计高度为1.63 m.     

青藏铁路五道梁地区冻土片石通风路基的气冷效果分析

以青藏铁路五道梁片石路基为研究实例,分析了片石层的工作原理,并与一般路基不同位置处的地温进行了比较,认为片石路基有利于保护冻土地温.在考虑空气对流作用的前提下,对五道梁片石路基进行了地温预测,结果表明,在预测前30年还能有效地保护冻土,而50年后其人为上限出现下凹形态.     

青藏铁路多年冻土区路基温度场的模拟与预测

在多年冻土区修建铁路站场路基,打破了原来天然地表与外界的热力平衡,地下温度场将重新分布.根据此特征可推断多年冻土的发展演化趋势以及评定路基的稳定状况.结合青藏铁路某段站场路基实际监测数据,利用ANSYS软件对2002年～2030年地下温度场进行有限元数值模拟.模拟计算结果表明:路基下冻土上限发生上移,多年冻土得到了保护;在年平均气温增长0.02 ℃的条件下,试验段内冻土人为上限和未受路基影响的冻土天然上限均逐年下降;同时,路基阳坡、阴坡两侧地下温度场分布特征的差异构成了路基不均匀变形和路面裂缝的潜在威胁.     

青藏铁路清水河段拼装式涵洞地温与沉降变形的变化规律

根据对青藏铁路清水河段拼装式涵洞工程监测的地（气）温及沉降累积变形数据结果，运用Excel进行整理、分析总结归纳出：在多年冻土区由于涵洞工程的修建，打破了原天然外界环境下冻土的热状况，引起涵洞基底下不同深度土体所受到的外界影响呈现出差异性；通过对涵洞基底土体地温和沉降变形年波动变化的分析，结果表明，在一个冻融循环期间涵洞冻胀抬升变形总值是低于融化下沉变形的；在经过一个冻融循环期后，涵洞从整体上呈现了一个逐渐下沉的趋势；由于各测孔沉降变形的不均匀性，将会导致涵洞工程在运营过程中出现一些病害。     

青藏高原多年冻土地区不良冻土现象对铁路建设的影响

在青藏高原高海拔地区修建铁路将遇到大片多年冻土 .讨论青藏高原多年冻土的分布规律和不良冻土现象及其对青藏铁路修建的影响 ,提出一个针对铁路建设的工程地质分区方案     

The Impact of Climate Warming on Permafrost and Qinghai-Tibet Railway

Global wanning is an inarguable fact. Permafrost is experiencing a change due to climate warming in Qinghai-Tibet Plateau, such as the decreasing of permafrost table, the rising of permafrost temperature, etc. On the basis of analysing the permafrost change under the climate change and engineering action, the thermal regime and spatial distribution of permafrost are predicted for air temperature rising 1℃ and 2.6℃ after 50 years in this paper. The results show that climate change results in the larger change for the thermal regime and spatial distribution of permafrost. Permafrost change will produce the great effect on the Qinghai- Tibet Railway engineering, not only resulting in the decreasing of permafrost table beneath the roadbed, but also resulting in thawing settlement due to the thawing of ground ice near permafrost table. The idea of cooling roadbed and actively protecting permafrost for the Qinghai-Tibet Railway engineering could adjust and control the permafrost thermal state, some better methods are provided to ensure the engineering stability in the areas of warm permafrost and high ice content.     

New discoveries on the effects of desertification on the ground temperature of permafrost and its significance to the Qinghai-Tibet Plateau

The desert and permafrost conditions of the Qinghai-Tibet Plateau are unique.However,the effects of desertification on the ground temperature of permafrost are currently unclear.Recently,understanding this problem has become more urgent because of increasing desertification on the plateau.For this reason,an observational field experiment was undertaken by the authors at Honglianghe on the Qinghai-Tibet Plateau.Thermistor ground temperature probes were used,and synchronized contrasting observations were made in an open area.Observations of the ground temperature of permafrost below sand layers with a range of thicknesses were made from May 2010 to April 2011.The sand layers were found to play a key role in the protection of the underlying permafrost.The ground temperature below a permafrost table overlain by a thick sand layer was lower than that of the average annual temperature for the natural ground surface,and the temperature drop was roughly constant at 0.2°C.During the warmer part of the year (May to September),the maximum temperature drops over the five months were 3.40,3.72,4.85,3.16,and 1.88°C,respectively.The ground temperature near a permafrost table overlain by a thin sand layer was also lower than that of the average annual temperature for the natural ground surface.However,in this case the average of the annual maximum temperature drop was significantly less,0.71°C.The scientific significance of our preliminary conclusions is not only to present an exploration of the interaction between desertification and permafrost,but also to provide new engineering ideas for protecting the permafrost in regions where construction is required on the Qinghai-Tibet Plateau.     

Experimental Study on Riprap Air-Cooled Roadbed of Qinghai-Tibet Railway

The riprap air-cooled roadbed and common roadbed experimental project were designed and carried on in Qingshuihe test filed, an area of warm permafrost category with the fine frozen soil along Qinghai-Tibet Railway, to decide the temperature field of the roadbed after railway construction. Based on ground temperature variation of natural hole, left and fight shoulder＇ s hole, the maximum thawing depth, and the deformation in these two kinds of roadbed were analysed comparatively. It showed that the riprap air-cooled roadbed had better effect of lowering ground temperature, lifting the maximum frozen-thawing depth obviously and decreasing deformation than that of the common roadbed. Therefore, the riprap air-cooled roadbed was a positive frozen soil protection measure for it effectively decreased ground temperature and protected permafrost.     

Application and Study on Dynamic Design in Qinghai-Tibet Railway Construction

0Preface Permafrostisasoilmediumwhichisextremely sensitivetotemperatureandsurroundingfactors.Themostessentialdistinctionbetweenpermafrost andotherrockorsoilisthatitcontainsground ice.Whileconstructinganystructureson permafrost,twomajorengineeringproblemsmustbesolved:freezingheaveinflationandthawing settlement.TheGolmud LhasaSectionofQinghai Tibet Railway,withatotallengthof1118km,hasa totaldistanceof632kmrunningonpermafrost,outofwhichabout550kmiscontinuous permafrost,82kmispatchypermafrost,9…     

软土地基上路堤拓宽工程的稳定性分析及处理对策

结合某湖滨路的拓宽改造工程,采用数值分析软件分析了软土地基上进行新路堤填筑对沉降的影响,并采用强度折减法研究其整体稳定性.数值分析结果反映出加宽后路堤的整体稳定的安全储备不足,新老路堤的差异沉降明显,需要采取加固处理措施.对两种不同的加固措施进行了研究,计算结果表明,采用水泥搅拌桩等进行软基处理能有效地提高路堤的整体稳定性.本文的实例研究对于类似工程可以起到参考和借鉴的作用.     

青藏铁路多年冻土场地波速特性分析

为分析冻土场地波速变化规律,通过现场钻孔波速测试,并结合已有典型场地波速资料,研究了青藏铁路沿线多年冻土场地波速比的经验值及波速变化受控制因素的影响规律。结果表明:多年冻土场地纵横波速比经验参考值可选用1. 5左右;冻土层波速传播规律与地温、土层埋深、土质属性、冻结冰晶含量等诸多因素相关;冻结作用使土体的结构性增强从而冻土体强度增强,冻结状态下土体的波速通常大于未冻结场地土体;多年冻土层波速值随土层深度的增加、地温的降低和冻结土体中冰晶含量的增加而增加。     

Discussion on the Designing Difficulties of Fenghoshan Tunnel on Qinghai-Tibet Railway

1ProjectProfile FenghuoshanTunnelofQinghai TibetRailwaylocatedatthelowerpartofhighmountainous regions,withbigundulatingtopography,well developedsurfaceditches.Themountain,which housesthetunnel,is4996mabovethesealevel.Thetunnelis1338mlong,thealtitudeofthetrackis4900m.Theclimateisoficeandsnow climateofQinghai TibetPlateau,dry,and constantlychanging.Thetemperatureandtheairpressureislow.Springandautumnareshort,the freezingseasonstartsinSeptemberandendsin Aprilnextyear.Accordingtotheobservati…     

A Roadbed Cooling Approach for the Construction of Qinghai-Tibet Railway

Over one half of the permafrost along the Qinghai-Tibet Railway is ＂warm＂ and approximately 40% ice-rich. Under global warming, the construction of the Qinghai-Tibet Railway needs to consider climate changes over the next 50 - 100 years. Recent estimates indicate that the air temperature on the plateau will increase by 2.2- 2.6℃ by 2050. Thus, the key to the success of the railway construction lies in preventing the permafrost underlying roadbeds from thawing. It has been more than 100 years since the first railway was build over permafrost. A frost damage ratio of greater than 30 % has been reported for all the railroads built in permafrost regions. Based upon the experience and lessons leamed from roadway constructions over permafrost, this paper proposes a more proactive design approach for the construction of the Qinghai-Tibet Railway. This approach focuses on cooling down the roadbed by lowering the ground temperature and is different from the passive method of preventing permafrost from thawing by simply increasing thermal resistance （e. g., increasing embankment height and using insulating materials）. This ＂roadbed cooling＂ design approach is especially relevant to ＂warm＂ and ice-rich permafrost areas. A number of measures can be taken to cool down the roadbed, including proper selection of roadbed material, and configurations to adjust solar radiation, heat convection, and heat conduction patterus in and/or around the roadbed.