Permafrost

16
Numerical analysis for thickness of fractured-rock revetment layer on
Qinghai-Tibet Railway
Bin-xiang Sun, Qi Liu, Xiao-zu Xu
(Department of Civil Engineering, Shaoxing College of Arts and Sciences, Shaoxing 312000, China)
Abstract: The non-dimensional governing equations for natural convection in variable
permeability porous media are derived. Triggering and evolution of winter-time natural
convection cooling effect in fractured-rock revetment embankments of Qinghai-Tibet Railway
are investigated by means of an air-flow function. So as to evaluate the effectiveness of the
cooling effect of winter-time natural convection in railway embankment with fractured-rock
revetment, the mean Nusselt number representing heat transfer through unit length at the base
of embankment was defined. The dependences of the average Nusselt number on thickness of
fractured-rock layer and temperature amplitude of embankment surface are analyzed using a
numerical representation of the non-dimensional governing equations for heat convection. The
analysis shows that the mean Nusselt number in fractured-rock revetment embankments
decreases early and then increases with increasing of temperature amplitude on the surface
instead of increasing monotonically. This decrease-increase effect during increasing of the mean
Nusselt number will rapidly weaken with increasing of temperature amplitude. The approach to
evaluation of critical thickness of fractured-rock layer in revetment embankments was
developed on the basis of the decrease-increase effect. Validity of estimating fractured-rock
revetment layer thickness in the railway embankment was demonstrated both numerically and
experimentally. Therefore, this evaluation approach in the present work is available for
construction of Qinghai-Tibet Railway.
Key words: Qinghai-Tibet Railway, fractured-rock revetment, natural convection, winter-time
cooling effect
Test and Analysis about the Development of Depth of Seasonal-Thawing
of L Type Retaining Wall
Bo Liang 1 , Yuan-ping Cao 2 , Jian-jun Ge 2 , Cheng Wang 1
(1. School of Civil Engineering and Architecture, Chongqing Jiaotong University, Chongqing 400074, China;
2. The First Railway Survey & Design Institute, Xi’an 710054, China)
Abstract: In permafrost region, the key about the stability of earth structure is itself thermal
stability. If retaining wall would be built in permafrost region, it would change the heat balance
of ground layer and the upper limit of frozen soil or depth of seasonal-thawing would change.
The stability of engineering structure would be affected by the heat balance change. So it is
value to study the development of the upper limit of frozen soil or temperature field distribution
according to the seasonal change. In this paper, considering the only retaining constructing - L
type retaining wall in section from Golmud to Lhasa, Qinghai-Tibet railway, we test the
temperature along the cross-section of retaining wall. We analyze the upper limit of frozen soil
or depth of seasonal-thawing of typical backfill. The distribution shape of depth of
seasonal-thawing in different cross-section has been obtained and the temperature field