青藏铁路块石气冷结构路堤下冻土温度场变化分析

基于青藏铁路沿线多年冻土区温度监测断面,选取了不同冻土分区中的8个块石路堤结构(块石路基、块石护坡、块石路基加块石护坡)断面,对其下温度场的变化分析研究.结果表明:经过2~3个冻融循环后,块石结构路堤下冻土上限已抬升了1.4~5.3 m,说明块石路堤结构已起到了积极调节下伏冻土温度的作用.结果也显示,在上限抬升的同时,其下部的冻土地温也在升高,但是这种过程已逐渐被块石路堤结构的降温所抑制,而这种抑制程度受控于不同的冻土区域.在不同的冻土分区中,无论是何种形式的块石路堤结构,其降温趋势是不同的.Ⅳ和Ⅲ冻土区块石路堤基底的负温积累比较明显,而I和Ⅱ区的较弱.

Analyses of the Temperature Fields within an Air Convective Embankment of Crushed Rock Structure along the Qinghai-Tibet Railway

On the base of in-situ monitoring the air convective embankment of crushed rock structure(included the crushed rock embankment, the embankment with crushed rock slope protection and the crushed rock embankment with crushed rock slope protection) along the Qinghai-Tibet Railway,eight monitoring profiles were chosen to analyze the change of ground temperature within an air convective embankment of crushed rock structure in permafrost region with different temperatures(Region I: T_cp≥-0.5 ℃;Region Ⅱ: -1.0 ℃ ≤T_cp<-0.5 ℃;Region Ⅲ: -2.0 ℃ ≤ T_cp<-1.0 ℃;Region Ⅳ: T_cp<-2.0 ℃,where,T_cp is the annual average ground temperature).After 2~3 freezing-thawing circles,the permafrost tables have risen 1.4~5.3 m,showing a positive effect of adjusting and cooling roadbed due to the building of the air convective embankment with crushed rock structure.Meanwhile,it is also revealed that the ground temperature below the permafrost table increases gradually at the initial stage of construction,along with the permafrost table rising.This process has been restrained by the air convective embankment with crushed rock structure.But the restraining effect is different from region to region,depending on temperature.The cooling effect of the air convective embankment with crushed rock structure in Regions Ⅲ and Ⅳ is stronger than that in Regions Ⅱ and Ⅰ.