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

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Vo1.82 No.5 PP.949—958 ACTA GE0L0GICA SINICA 0ct.2008 Permafrost Characteristics of the Qinghai-Tibet Plateau and Methods of Roadbed Construction of Railway 

NIU Fujun 1 ’,XU Jian ,LIN Zhanju ,WU Qingbai and CHENG Guodong 1 State Key Laboratory ofFrozen Soil Engineering,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy ofSciences,Lanzhou 730000,China 2 Cold Regions Road Engineering Laborator3,.the Ftrst Highway Design and Research Institute.Xi an 71 0068,China 

Abstract: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. 

Key words:permafrost,roadbed,cooling method,Qinghai・Tibet railway 

1 Introduction The Qinghai—Tibet Plateau(QTP)is the highest plateau around the world.Permafrost covers an area of ca. 1.500.000 km .which accounts for 75%of the area of the plateau(Zhou et a1.,2000).High altitude,cold climate, and lack of the oxygen make its environments very weak to disturbance.Permafrost and harsh environment makes railway construction more dificult.The Qinghai—Tibet railway(QTR)was started to construct in 200 1,finished in 2006 and opened to service in 2007.Now it has been the newest huge project in the permafrost regions around the world.However.it was constructed after around 30 years of intermittent planning,discussion and investigation since 1 970’s.During the design and construction of the railway,there were three dificulties, including lack of the oxygen,permafrost problem and environmental problem,with the permafrost problem being the hardest and key one. The permafrost in the QTP has characteristics of high ground temperature(warm content(ice.rich Dermafrost] Corresponding author.E—mail permafrost)and high ice— Roadbed stability is directly niufujun@lzb.tic.cn influenced by its distribution.thermal status.ground ice content and changing trend.Monitored data from the boreholes in the natural ground without any disturbance along the Qinghai—Tibet highway(QTH)showed that,the ground temperature at the permafrost table increased at a rate of 0.08。C/a from l996 to 2001.And the table lowered at a rate of 2.6—6.6 cm/a.According to investigations in past 30 years.the mean annua1 ground temperature fMAGT)of the seasonal frozen ground and island permafrost along the QTH increased 0.3。C-0.5。C from l970’s to l990’s.The MAGT of the continuous permafrost increased 0.1。C_JO.3。C within the period. Many studies show that permafrost is warming,thawing, and degrading during the past few decades on the QTP (Cheng and Wu,2007).Moreover,Qin(2002)predicted the climate on the QTP would possibly increase with a value 2.2。C-2.6。C by the year of 2050.considering influences of climate and human activities.Under such conditions.incessant degradation of the permafrost in the region will eventually do harm to stability of the local englneenng projects. In the past several years.many indoor experiments. numerical simulations and field testing work on the 

重庆维普 http://www.cqvip.com950 Permafrost Characteristics of Qinghai—Tibet Plateau and Roadbed Construction of Railway Niu et al roadbed constmction methods proposed based on the proactively cooling principle have been proceeded.This paper summarizes the roadbed configurations,thermal mechanisms and their effectsbased onfieldworks. 

2 Characteristics of Permafrost and 35。N Their Influence on the QTR 

2.1 The characteristics of permafrost along theOTR The QTR is situated in the hinterland of the QTP;the length of the section from Golmud to Lhasa is 1,142 km,of which the length traversing the permafrost area is about 632 km. The northern limit of the permafrost is 1ocated in the Xidatan Basin north to the Kunlun Mount ̄n.The south limit is located in the Anduo Basin south to the Tanggula Mountain (Fig.1).111e permafrost along the QTR is