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1.
Finite Element Method has been used to operate the numerical analysis and comparison between the traditional ventilated embankment and the adjustable ventilated embankment adopted in Qinghai-Tibet Railway construction. The numerical results show that: 1) The adjustable ventilated embankments can prevent the thermal entry from air into ducts during summer from thawing the permafrost beneath the embankments; 2) The cooling effects of the adjustable ventilated embankments on permafrost is much better than the traditional ventilated embankments although two kinds of embankments can generate the thawing bulbs at the beginning of finishing construction; 3) The drop of the mean temperature of permafrost under the adjustable ventilated embankments keeps faster than that of the mean temperature of permafrost under the traditional ventilated embankments. It is clear that the adjustable ventilated embankments can keep the embankment more stable than the traditional ventilated embankments. 相似文献
2.
In permafrost regions, many methods about active cooling embankment are put forward, one of these representations is ventilated embankment, its cooling effect is the result of the air convection in the duct, and this leads to reducing the annual average ground temperature. The present work in this article is to determine the boundary conditions of the ventilated embankment and natural ground in numerical work. There are several effects which influence boundary conditions, they are: radiation, evaporation,phase change, convection and embankment material etc. Radiation and convection are the main effects in those. We mainly consider sun radiation in this article. The added-surface effect in ventilated embankment lowers its temperature, so the temperature on the wall of the ventilated embankment is different from the temperature in atmosphere. There are two methods in determining the surface temperature, experimental method and experiential method. Detailed research is discussed in the article. 相似文献
3.
Abstract: Permafrost (perennially frozen ground) appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature (≥ ?1°C) and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope (ECRSS) were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the “cold” energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway. 相似文献
4.
冻土地区三角形块石路基与水平块石路基的保冷效果研究 总被引：2，自引：2，他引：0
Time varying temperatures and pore-air velocities in two gravel embankments, horizontal and triangular gravel embankments, are studied using the "Rock-Block model" and the results are visualized in the form of isotherms and velocity vectors for different times of the year. Simulation results show that for both the two embankments there is a counter-clockwise rotation of pore-air extending throughout most of the embankment during winter months, whereas in summer the pore-air rotation changes to the opposite. The pore-air velocities in the triangle gravel embankment are somewhat higher than those obtained from the horizontal gravel embankment. The stronger convection in winter enhances the upward transport of heat out of the triangle gravel embankment, thus having more apparent cooling effect than the horizontal gravel embankment. During summer months, the pore-air velocities are nearly the same for both the two embankments. The results of the present study show that though the two gravel embankments have the effect of cooling the permafrost beneath, the temperature fields in the triangle gravel embankment are a little lower and more stable compared with those gotten from the horizontal gravel embankment, showing that the triangle gravel embankment has more apparent cooling effect than the horizontal one. 相似文献
5.
Aiming at the stabilization of Qinghai-Tibetan Railway embankment during its construction and run, the method using tilt pipes to keep the permafrost embankment stabilization is put forward in the paper. By gathering natural cold energy in the winter and release it in the summer the tilt pipes can keep the permafrost embankment stabilizing. The temperature fields of the embankment and the stratums below are studied according to the condition of pipes diameter 250mm, length 7. 0m and tilt angle 30°,45°, 60° until the railway working for 20 years. It is shown that the embankment field using tilt pipes will eliminate the thawing core and come into subzero temperature phase ahead of 9 years compared with the original model. Different tilt angles have different efforts on the embankment and stratums, synthesis analysis of thermal income and expenses of the embankment and stratums should be carried out 相似文献
6.
青藏铁路冻土路基沉降变形现场试验研究 总被引：3，自引：0，他引：3
Based on the field data of ground temperature and roadway settlement observed during the construction of the experimental embankments over permafrost along the Qinghai-Tibetan Railway, this paper discusses the differences of frost process on the roadway surface from that on the natural ground surface, the changes of permafrost table under the roadway embankment, and the peculiarities of roadway settlement. Analyses of the test results show : 1) The differences of the freezing indexes between the roadway surfaces and the natural ground surfaces are less than those of the thawing indexes for all the test sections; 2) Since the measures of permafrost protection were taken, the permafrost tables under the embankments have raised after the roadway was constructed. The minimum is about 0.4 m and the maximum is 1.2 m; 3) the settlements of the roadway are mainly from the compression and creep of the icerich frozen soils under the original permafrost tables and the maximum has reached 6 ～ 8 cm during the first year after the embankments were constructed. Moreover, concerning the processes of roadway settlement, the deformation of the embankments has no obvious trend of attenuation at present. Especially,for the roadway with high embankments, the settlement may reach a remarkable value and much consideration must be given for this problem. 相似文献
7.
青藏高原多年冻土区地温监测结果分析 总被引：6，自引：0，他引：6
Ground temperatures monitored at four observation sites in permafrost regions on the Tibetan Plateau was analyzed. It was found that the ground temperature at the depth of 12～20 m increased 0.2～0.4 K and the permafrost thickness decreased 4～5 m from the base in Xidatan Site from 1975 to 1989; and the ground temperature at the depth of 6～15 m increased 0.2～0.4 K in Kunlun Pass Site from 1982 to 1997. Contrast observations show that a sand cover, 15～20 cm in depth, can result in a ground temperature decrease of 0.1～ 0.2 K in MS66 Site; and a removal of vegetation can result in a ground temperature decrease of some 0.2 K in Hoh Xil Site. The monitor demonstrates that many factors that control permafrost developing have duality, e.g., sand and vegetation are able to increase or decrease the ground temperature. These factors, in conjunction with permafrost behaviour, play different roles under different conditions. Therefore, it is necessary to study, understand and evaluate permafrost and its engineering geological properties taking the viewpoint of dynamic variation. 相似文献
8.
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. 相似文献
9.
Zheng Haifei Xie Hongsen Xu Yousheng Song Maoshuang Zhang Yueming Wang Mingzai Xu Huigang Department of Geology Peking University Beijing Institute of Geochemistry Chinese Academy of Sciences Guiyang Guizhou 《《地质学报》英文版》1996,70(2):157-167
The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere. 相似文献
10.
Kenji Yoshikawa Vladimir Romanovsky Nataria Duxbury Jerry Brown Alexandre Tsapin 《冰川冻土》2004,26(Z1):301-309
Direct current resistivity and ground penetrating radar surveys were employed to obtain the value of the resistivity and dielectric constant in the brine near the Barrow, Alaska. The geophysical surveys were undertaken together with the permafrost drilling program for the measuring of the ground temperature regime and for the core sampling. The sampled cores were measured for their physical and chemical properties in the laboratory under different temperature conditions (-60 to 20 ℃). Laboratory results support field observations and led to the development of a technique for distinguishing freshwater taliks and brine layers in permafrost. These methods were also employed in freshwater taliks near Council,Alaska. The electrical resistivity is a powerful and sensitive parameter for brine detection. However, the resistivity is a less sensitive indicator of the soil type or water content under highly saline conditions.High frequency dielectric constant is an ideal second parameter for the indication of the soil type, liquid water content and other physical properties. The imaginary part of the dielectric constant and resistivity have a significant dependence upon salinity, i.e. upon freezing temperature. The ground temperature regime and the freezing point of the brine layer are important parameters for studying the electric properties of permafrost terrain. 相似文献
11.
青藏铁路多年冻土区普通路基热状况监测分析 总被引：1，自引：1，他引：0
基于现场地温监测数据,选取年平均地温不同的监测断面对青藏铁路普通路基的热状况进行分析,包括多年冻土上限变化及其地温变化、下伏多年冻土温度变化、原天然地表附近热收支等方面. 结果表明：在低温多年冻土区,路基下部多年冻土上限均有所提升,且新近形成的人为上限较为稳定,冷季时负温积累显著;路基下伏多年冻土总体热稳定性较好. 而在高温多年冻土区,左（阳坡）路肩下部多年冻土上限多表现为下降,右（阴坡）路肩下部多年冻土上限有升有降,但是新近形成的上限均温度较高且有进一步升温的趋势;与天然场地地温相比,路基下部多年冻土均出现一定的升温. 尤其在高温极不稳定多年冻土区,天然场地多年冻土自身处于吸热升温状态;路基修筑后,下部多年冻土已经出现了融化夹层及双向退化的情况,路基热稳定性较差. 对于普通路基来说,由于青藏高原强烈的太阳辐射及青藏铁路总体走向原因,普通阴阳坡效应显著,左、右路肩下部多年冻土热稳定性差异较大. 相似文献
12.
青藏铁路多年冻土区含融化夹层路基的热状态 总被引：1，自引：1，他引：0
基于青藏铁路K1496+750监测断面含融化夹层路基长达10 a的地温监测数据,分析了在气候转暖及工程活动下天然场地及路基左右路肩下多年冻土热状态年变化过程、融化夹层的年变化过程及其对多年冻土热状态的影响。结果表明：监测断面天然场地、左右路肩下多年冻土上限逐年下降,热稳定性逐年降低;观测期内,左路肩下发育有融化夹层,融化夹层厚度在波动中呈增厚趋势,且其增厚主要是由多年冻土人为上限下降所致,而天然场地及右路肩下未发育融化夹层;多年冻土上限附近土体热积累显著,进而导致多年冻土上限逐年下降及其附近土体温度逐年升高,弱化了多年冻土的热稳定性;后期增加的块石护坡和热管两种具有“主动冷却”效能的工程补强措施很好的改善了路基的热稳定性,右路肩经工程补强措施后,多年冻土人为上限得到显著抬升,热稳定性得到显著改善,而左路肩由于融化夹层的存在,工程补强措施仅仅维持了当前多年冻土热状态,融化夹层的存在一定程度上弱化了工程补强措施所产生的冷却效能。 相似文献
13.
块石路基是多年冻土区应用最为广泛的多年冻土路基形式. 为了研究多年冻土区修筑高速公路后块石路基的效果,选取青海省新建共和-玉树高速公路3个块石路基监测断面的实测资料,对路基修筑初期多年冻土温度状况进行了分析. 结果表明：路基修筑初期路基中心原天然地表下0.5 m处仍表现出季节变化规律,至原多年冻土上限深度处,温度波动幅度急剧减小. 块石路基的保温效果与年平均地温密切相关,年平均地温越低,对冻土的保护效果越显著. 受阴阳坡效应的影响,左路肩/坡脚温度高于右路肩/坡脚. 左右路肩及中心孔下多年冻土上限都得到不同程度的抬升,抬升幅度主要受路基高度影响,与多年冻土年平均地温没有必然关系. 相似文献
14.
青藏高原多年冻土区碎石护坡降温作用及效果分析 总被引：6，自引：3，他引：3
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. 相似文献
15.
青藏铁路普通路基下部冻土变化分析 总被引：5，自引：2，他引：3
高温高含冰量冻土地区,青藏铁路采取了冷却路基、降低多年冻土温度的工程措施.然而青藏铁路仍有大量路段未采用任何工程措施,因此修筑普通路基后冻土变化也是普遍关心的问题.根据青藏铁路普通路基下部土体温度监测的近期结果,分析了季节冻土区、已退化多年冻土区和多年冻土区路基下部冻土变化特征.结果表明,不同区域修筑普通路基,其下部土体温度、最大季节冻结深度、多年冻土上限等存在较大的差异.在季节冻土和已退化多年冻土区,右路肩下部(阴坡)已形成冻土隔年层;在多年冻土强烈退化区,其路基下部形成融化夹层;在高温多年冻土区,其路基下部上限存在抬升和下降,上限附近土体温度有升高的趋势.在低温多年冻土区,其路基下部上限全部抬升,上限附近土体存在"冷量"积累,有利于路基下部多年冻土热稳定性.因此,低温多年冻土区修筑普通路基后,冻土变化基本是向着有利于路基稳定性的方向发展,在其它地段修筑普通路基,冻土变化是向着不利于路基稳定性的方向发展的.特别是阴阳坡太阳辐射差异,导致了土体热状态和多年冻土上限形态产生较大的差异,这种差异将会对路基稳定性产生一定的影响. 相似文献
16.
利用小波变换分析方法, 对青藏公路风火山监测场地天然状态下和路基中心下15 a的低温多年冻土温度时间序列进行了多时间尺度分析和趋势预测. 结果表明: 天然地表和路基下部多年冻土温度变化具有多时间尺度特征, 二者多时间尺度周期的时频分布特征存在较大差别. 天然地表具有简单的规律性, 路基中心的规律相对较复杂, 主要体现在冻土上限附近. 天然地表下当前均处于暖期, 深层主要受气候长周期波动控制, 使其在进入冷暖期的时间上滞后于上层; 路基中心下浅层和深层的冷暖期相反, 浅层处于暖期, 深层处于冷期, 其长度随热交换量大小和热量积累的变化也不统一, 给路基的稳定性带来了更大的隐患, 但也为控制、减少和治理冻土路基中的病害提供了新依据. 相似文献
17.
青藏铁路路基创造性采用了主动冷却路基的设计理念修建而成,目前铁路已经安全运营超过10年。青藏铁路路基修筑在多年冻土之上,路基下部冻土温度变化是衡量路基是否稳定的关键因素。基于长期（2008—2019年）地温观测资料,对昆仑山垭口南坡青藏铁路K980+000低温多年冻土区块石路基坡脚至坡脚外30 m范围内的冻土上限变化、年际地温变化、季节性地温变化进行分析,研究了路基工程行为对低温多年冻土的长期影响机制。结果表明：冻土地温不断升高,冻土上限逐年下移;与天然孔比较,路基坡脚处地温增温幅度反而较小,主要可能受块石路基冷却效应的影响;冷季与暖季呈现出不对称的增温趋势。冻土路基普遍增温的趋势仍然存在,出于对多年冻土的保护与保证工程稳定性的考虑,应尽量采用冷却路基的思想修建路基。同时,应加强对路基的监测,分析长期增温过程后路基稳定性变化,并对路基下部冻土的变化做出定量研究。 相似文献
18.
保温处理措施在多年冻土区道路工程中的应用 总被引：26，自引：11，他引：26
阐述了保温处理措施保护多年冻土的原理, 认为保温材料下部地温年变幅的减小是保温处理措施保护多年冻土上限下降的主要效果. 青藏公路昆仑山越岭地段保温处理试验路段路基、路肩及天然地表下的地温观测资料证实, 保温处理处理措施并不能改变因修筑路基而引起的路基吸热趋势, 但是保温处理后浅层地温下降; 地温年变幅明显减小, 多年冻土上限比无保温处理路段高. 青藏铁路北麓河试验段保温处理试验路段半年的观测资料表明, 保温层上下面温度存在巨大差异, 充分体现了保温材料的热阻效应, 可望大幅度减小保温材料下部地温的年变幅, 起到保护或延缓多年冻土融化的效果. 相似文献
19.
多年冻土南界附近青藏铁路路基下的冻土退化 总被引：1，自引：0，他引：1
基于2006-2012年青藏铁路多年冻土区唐古拉山南侧安多断面地温监测资料,分析了多年冻土南界附近路基下多年冻土的退化过程及其影响因素.结果表明：该监测断面天然场地多年冻土退化表现为多年冻土天然上限下降与多年冻土地温升高,观测期内多年冻土天然上限下降0.29 m,下降速率为4 cm·a-1;路基下10 m处多年冻土温度升高0.03℃,升温速率为0.004℃·a-1.该监测断面路基左路肩下多年冻土退化表现为多年冻土人为上限下降、多年冻土地温升高、多年冻土下限抬升以及多年冻土厚度减少.观测期内多年冻土人为上限下降0.41 m,下降速率为6 cm·a-1;路基下10 m处多年冻土地温升高0.06℃,升温速率为0.009℃·a-1;多年冻土下限抬升0.50 m,抬升速率为7 cm·a-1;多年冻土厚度减少0.90 m,减少速率为13 cm·a-1.工程作用是导致路基下多年冻土退化的主要原因,气温升温与局地因素中的冻结层上水发育促进了这一退化过程.路基下融化夹层的出现,导致多年冻土垂向上由衔接型变为不衔接型. 相似文献
20.
青藏铁路碎石护坡-热管复合措施的补强效果研究 总被引：2，自引：1，他引：1
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. 相似文献