青藏铁路通风路堤室内模型试验研究

LABORATORY STUDY ON VENTILATION DUCT ROADBED OF QINGHAI-TIBET RAILWAY

正在建设中的青藏铁路即将穿越 5 5 0km的多年冻土区 ,冻土问题是青藏铁路面临的首要工程问题。出于铁路建设中保护冻土的原则 ,对通风路堤这一新的、主动保护冻土的路堤结构形式进行了几何相似比为 1∶4的大型室内试验 ,试验所得的路堤土体温度场分布及土体温度的变化结果表明 ,通风路堤能够有效地降低路堤土体的温度 ,从而达到保护天然地基冻土的目的。但是 ,温度场的分布在通风路堤内并不对称 ,及沿路堤中轴线的两侧左右不对称 ,这样可能会影响到下伏冻土温度的差异 ,从而引起不均匀冻胀、沉降变形。另一方面 ,暖季较高的气温条件下 ,通风管两端的进出口需要堵塞或关闭 ,以免造成土体吸热量较多而引起较大的沉降 ,但由于青藏高原很短的融化期 ,这一影响还有待现场试验工程的验证。

The efficiency of using ventilation ducts in the roadbed for the Qinghai Tibet railway are studied by comparing data from two large scale laboratory experiments,in which,the temperatures were varied for roadbeds constructed with and without ventilation duct,and the temperature distribution was monitored spatially.The results of the experoiments confirmed that it is wasier to freeze the pore water within the railway roadbed under temperature below 0 ℃ when ventilation duct are used,and that the ventilated roadbed is efficent in protecting existing frozen ground from thawing and can even extend the frozen zone. However,the temperature distrbutions along a direction parallel to the ventilation ducts are uneven,and it also varies with different distances from the duct, so that the temperure is uneven in three dimensions. As a consequence,uneven heave and thawing deformations might be caused in real projects which is under construction .The open ended ventilation ducts should be closed in warm seasons to prevent additional thawing settlement from occurring. The conclusions have led to recommendations for the design of a field experimental project using ventilated roaded along the Qinghai Tibet railway in the Beiluhe region,where huge underground ice layers are very common.