Permafrost

40
Analysis of Temperature-control Effect on Particle Improved Roadbed
in Permafrost
Ming-kui Huang 1 , Ren Wang [2 , Ming-jian Hu 2 , Xue-fu Zhang 1
(1. School of Civil Engineering and Architecture,Chongqing Jiaotong University,Chongqing 400074,
China;2. Key Laboratory of Rock and Soil Mechanics,Institute of Rock and Soil Mechanics,Chinese
Academy of Sciences,Wuhan 430071,China)
Abstract: The total length of the Qinghai-Tibet railway is 1,118km. 632km of the railway must
build on the permafrost. Therefore, it is the primary task for many researchers to provide right
measures for the stabilization of the roadbed during its construction and operation. Because of
the warming of global climate, the average air temperatures in Qinghai-Tibet plateau keep
rising annually, which results from the degeneration of frozen soil. So these researchers have to
face the great challenge to protect the frozen soil from thawing. Based on large amount of
practical engineering experiences, they adopt some design principles and provide the design
theory of active cooling roadbed, thus promote the development of the frozen soil protection.
For the Qinghai-Tibet railway, one of the important tasks is to keep the stabilization of the
roadbed, and the thermal stability is one of the key factors. It has become the main task of
engineering construction in permafrost to select the right engineering measures and proper
roadbed structure for the prevention of harmful effects caused by the thermal conditions change
of the frozen soil. Today there are many measures for the protection of permafrost roadbed.
These measures could be generally classified into two groups. One is the passive measures such
as laying the insulation materials into the roadbed or simply raising the roadbed itself. The other
is the active measures, such as burying ventilation pipe, using ballast, block-stone roadbed or
revetment, adopting thermal rod, and so on. In this paper, the measure of particle improved
roadbed is presented. It is mainly through the filtering and restructuring of the roadbed-filling
granules to change the original structure of the roadbed, thus to create the physically improved
layer of combined particles for different requirements, which change the mutual heat-exchange
of the roadbed and the atmosphere for the protection of the frozen soil. Theoretically speaking,
this measure belongs to the scope of convection adjustment and control. In cold season this
measure with the big inner pore space could form the strong free convection with the change of
density differences of the atmosphere, which enable the continuous coldness exchanges. While
in warm season this measure could shield heat because of the difference of the conductive
coefficient between the air and the soil.
Based on the ground-temperature observation on the particle improved roadbed in Beiluhe
test field of Qinghai-Tibet railway, this paper makes an analysis of the characteristics of the
ground temperature changes and the temperature-control effect of the particle improved
roadbed, comparing with other similar protection measures. The result indicates that in certain
range of depth the ground temperature of the particle improved roadbed changes in different
seasons, depicting a sinusoidal curve. With the increment of the depth, the changes of ground
temperature lag behind the changes of the outside surroundings. Compared with the normal
roadbed, the particle improved roadbed has a generally lower ground temperature whether in
cold or warm seasons. To some extent, the upper limit of the frozen soil rises and from the
annual average ground temperature curve it shows the effect of cooling roadbed and protecting