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为了分析多年冻土拓宽路基差异沉降变形特征及形成机理,在青藏公路楚玛尔河地区开展了冻土拓宽路基试验研究,分析了路基拓宽后冻土地温、冻土上限、路基变形、新旧路基差异沉降变化特征以及拓宽路基对旧路的附加影响。结果表明:冻土路基拓宽后改变了坡角处原有的水热交换条件,造成新建拓宽路基下部多年冻土出现迅速升温退化;现场路况调查以及分层沉降监测显示新建拓宽路基在运营后发生大幅沉降变形,沉降主要集中在新旧路基结合处,变形主要来自于地表下2~3m处土层的压缩固结,该层土处于原天然地表下冻土上限附近,表明冻土融化下沉是导致拓宽路基发生沉降的主要原因;新旧路基间差异沉降量达到6cm,造成路基横坡改变率达到0.8%,超过《公路路基设计规范》(JTG D30—2015)中横坡改变率0.5%的上限要求;路基拓宽后使得黑色路面宽度增加,进而导致吸热量增加,加之拓宽路基产生的附加荷载,导致旧路中心处沉降在路基拓宽后初期内迅速发展。
In order to analyze the characteristics and forming mechanism of permafrost differential subsidence deformation and its formation mechanism, the permafrost embankment is expanded on the Qinghai-Tibet Highway, and the effects of permafrost temperature, permafrost upper limit, subgrade deformation, The characteristics of differential subsidence and the additional effect of widening the embankment on the old road. The results show that the widening of the permafrost embankment changes the original conditions of water and heat exchange at the slope angle, resulting in the rapid thermal degradation of the permafrost in the lower part of the new expanded embankment. The investigation of the road conditions and the monitoring of stratified settlement show that the newly built widened embankment occurs after operation Subsidence and settlement are mainly concentrated in the junction of old and new roadbed. The deformation mainly comes from the compression and consolidation of the soil layer 2 ~ 3m below the surface. This layer of soil is near the upper limit of the original natural subsurface permafrost, indicating thawing and thawing of frozen soil is Which led to the widening of the main reasons for the subsidence of the embankment. The differential settlement between the old and new embankments reached 6 cm, resulting in a 0.8% change rate of the cross-slope of the embankment, exceeding the upper limit of 0.5% of the ramp change rate in the “Code for design of highway subgrade” (JTG D30-2015) The widening of roadbed makes the width of black pavement increase, which in turn leads to the increase of heat absorption and the additional load of widening of roadbed. As a result, the settlement at the center of old road develops rapidly in the initial stage of roadbed widening.