Ground temperature characteristics of block stone embankment and traditional embankment at Beiluhe along Qinghai-Tibet Railway

During 2002～2003,a test embankment was constructed at Beiluhe along the Qinghai-Tibet Railway using coarse(25～30 cm),poorly graded block stone beneath the traditional embankment(TE) in permafrost with high ice content,which should be called the block stone embankment(BSE).The highly permeable BSE installation was designed to test the cooling effect of BSE concept with traditional embankment in an actual railway project.Using thermistor sensor strings with datataker,ground temperature data were automatically collected from the test section.Based on the ground temperature data measured in the boreholes within the BSE and TE after 3 freezing-thawing circles,the ground temterature variation at the original ground surface and the original natural permafrost table beneath BSE and TE and the ground temperature inter-annual variation of soil beneath BSE and TE were analyzed.It was shown that the cooling effect was obvious beneath BSE and the ground temperature was 0.4～0.9 ℃ and 0.3～0.6 ℃ lower than that of the TE at the original ground surface and the original narural permafrost table respectively.It was found that the cooling range of soils beneath the BSE was 3 m and 2 m larger than that of the TE beneath the north-facing shoulder and the embankment center respectively.Larger cooling rang would be favorable to restrain the warming of deep permafrost,which enhanced the thermal stability of embankment.Convection occurred between air in the block stone layer and environmental atmosphere differed at different parts of the BSE and it was strong,middle and weak beneath the north-facing shoulder,the embankment center and the south-facing shoulder respectively.