The Qinghai-Tibet Railway (QTR) project was finished on July 1 2006

and has served for over five years. Judging from the present situation

the roadbed is stable and train speed in permafrost regions achieves 100 km/h as expected during the designing. However

as half part of the roadbed was constructed over the permafrost characterized by high ground temperature and high ice-content

slight changes of the permafrost might lead to roadbed problems

of which the settlement in embankment-bridge transition section is an obvious and special one. Investigated results of 164 bridges from the Xidatan Basin to the Chiqu Valley along the QTR showed that the settlement was influenced by factors including bridge orientation

embankment slope direction

embankment height

ground temperature

ground ice-content of permafrost and local subgrade soil type. For the average value of the settlement

it was greater at the northern end of a bridge than that at the southern end

and was greater in sunny-slope than that in shady-slope. It was greater in high-ice permafrost regions than that in low-ice regions

and was greater in high-temperature permafrost regions than that in low-temperature regions. Additionally

it increased logarithmically with the height of the embankment. In regions where the subgrade soils were dominated by silt

silty clay or fine sand

the settlement amount was higher than that in bedrock regions. Correlation analysis results show that there are good relationships between the settlement and the slope direction

embankment height

ground temperature and ice contents when some of the later items are quantified. And the correlation coefficients are 0.234

0.213

-0.21 and 0.151 respectively

when the factors are quantified.