高海拔多年冻土区路基工程行为对低温多年冻土长期影响的监测研究

Long-term effects of embankment engineering behaviors on cold permafrost in high-altitude permafrost regions

青藏铁路路基创造性采用了主动冷却路基的设计理念修建而成,目前铁路已经安全运营超过10年。青藏铁路路基修筑在多年冻土之上,路基下部冻土温度变化是衡量路基是否稳定的关键因素。基于长期(2008—2019年)地温观测资料,对昆仑山垭口南坡青藏铁路K980+000低温多年冻土区块石路基坡脚至坡脚外30 m范围内的冻土上限变化、年际地温变化、季节性地温变化进行分析,研究了路基工程行为对低温多年冻土的长期影响机制。结果表明:冻土地温不断升高,冻土上限逐年下移;与天然孔比较,路基坡脚处地温增温幅度反而较小,主要可能受块石路基冷却效应的影响;冷季与暖季呈现出不对称的增温趋势。冻土路基普遍增温的趋势仍然存在,出于对多年冻土的保护与保证工程稳定性的考虑,应尽量采用冷却路基的思想修建路基。同时,应加强对路基的监测,分析长期增温过程后路基稳定性变化,并对路基下部冻土的变化做出定量研究。

The Qinghai-Tibet Railway(QTP)embankment was constructed based on the method of active cool⁃ing embankment.At present,the railway has been safely operating for more than 10 years.The subgrade of QTP is built on the permafrost,and temperature change of the permafrost under the subgrade is a key factor in measuring the stability of the subgrade.Based on the long-term(2008—2019)observation,the permafrost table and the annual ground temperature in five boreholes which were drilled within 30 m range to the slope foot mile⁃age K980+000 was analyzed.Inter-annual ground temperature changes and seasonal temperature changes were analyzed and the long-term effects of engineering behavior on cold permafrost were examined.The results show that the permafrost temperature has been increasing and permafrost table has been decreasing.Compared with the natural hole,the ground temperature of the borehole at the foot of the slope is less increased by the cooling ef⁃fect of the roadbed.The cold season and the warm season are asymmetrical.Due to the consideration of the pro⁃tection of permafrost and the stability of the project,the roadbed should be built with the idea of cooling roadbed as much as possible,so that the ground temperature at the foot of the roadbed slope is lower than the temperature of the frozen soil under the natural state,but the roadbed of the frozen soil is generally warmed.The trend still exists.At the same time,the monitoring of the subgrade should be strengthened,the stability of the subgrade af⁃ter the long-term warming process should be analyzed,and the quantitative study on the change of the frozen soil under the subgrade should be processed.