高温冻土区块石护坡路基长期热状况观测与预测研究

Field Observation and Prediction of Long-Term Thermal Regime of Crushed Rock Revetment Embankment Built on Warm Permafrost

块石护坡在多年冻土区路基工程建设和维护中已得到广泛应用。近年来,有关块石护坡的降温效能存在一些争议,尤其是在高温冻土区其能否抵御气候变暖的不利影响这一问题引起了学者的关注。基于青藏铁路近20年现场观测数据和数值模拟预测,探讨气候变暖背景下高温冻土区块石护坡路基50年内的热状况演化规律以及天然场地高温冻土退化过程。结果表明:块石护坡路基能够有效抬升人为冻土上限,路基运营20年后人为冻土上限较原天然上限仍有近2 m的抬升;路基运营20年内,浅层冻土地基存在明显升温过程,导致人为上限以下形成厚度达6~8 m的高温冻土层,其压缩和蠕变变形可引发量值可观的路基沉降变形;在50年气温升高2.6℃情景下,路基运营30年后人为冻土上限下降至同期天然场地冻土上限水平,此后路基人为上限与天然冻土上限同步下降,会进一步引发显著的路基沉降变形。对于高温冻土区块石护坡路基而言,依据路基热状况和变形发展过程,适时采用如热管类的补强措施是必要的。

Crushed rock revetment embankment(CRRE)has been widely used in the construction and reinforcement of highways and railways in permafrost regions.However,there have been controversies in recent years on the cooling effectiveness of CREE.Especially,debates around whether the CREE built on warm permafrost could withstand adverse effects of future climate warming have been drawing attention in academia.Based on the fieldobserved data and numerical simulations along the Qinghai-Tibet Railway in the past 20 years,this study explores the long-term thermal regime of CRRE built on warm permafrost and the degradation process of warm permafrost in the context of climate warming.The results show that the CRRE can effectively raise the artificial permafrost table.After nearly 20 years of operation,the artificial permafrost table beneath the CRRE still rises by nearly 2 m compared with the original.However,during this period,there has been a warming process in the shallow permafrost subgrade.A warm permafrost layer with a thickness of 6-8 m developed beneath the artificial permafrost table.The compression and creep deformation of the layer can cause considerable embankment settlement.Till 30 years after the embankment construction,the artificial permafrost table under the embankment has declined to the same level as that of the natural permafrost table under the scenario of air temperature rise of 2.6℃in 50 years.From then,the artificial permafrost table under the embankment and the natural permafrost table have declined almost synchronously,and the thawing of shallow permafrost subgrade will cause excessive embankment settlement.Therefore,for CRRE built in warm permafrost regions,it is necessary to timely adopt reinforcement measures such as thermosyphone,based on variations in the permafrost subgrade temperature and development of the embankment settlement.