道砟层对多年冻土区铁路路基水热影响监测与分析

Monitoring and Analysis of Impact of Ballast Layer on Thermal-moisture Dynamics in Railway Subgrade in Permafrost Regions

为分析道砟层对路基水热状况的影响,在青藏铁路北麓河试验段南侧布置监测断面,分别对天然场地、无道砟覆盖路基、有道砟覆盖路基下部一定范围地温、水分、热通量进行监测。结果表明:道砟大空隙、灰白色碎石覆盖层能有效阻止外部热量进入路基;有道砟覆盖路基比无道砟覆盖路基融化期短20d,5cm深度处有道砟覆盖路基比无道砟覆盖路基年平均温度低2.3℃,道砟层起到良好保温隔热作用;道砟覆盖层对水分有润湿和蒸发作用,有效减少大气降水入渗,保持路基水分相对稳定;夏季短期、高频次降雨有降低地表温度的作用,短期内对道砟层下水分和热量有明显影响,但降水几乎全部蒸发,未能在路基内形成水分累积,有道砟覆盖路基下部50cm深度处温度和含水量基本不受降雨影响。

To better understand the impact of the ballast layer on the thermal-moisture dynamics of Qinghai-Tibet Railway in the permafrost regions,a test section was built near Beiluhe permafrost monitoring station,to measure the ground temperature,moisture and heat flux under the natural ground,roadbed without ballast,and ballast covered roadbed.Collected data indicated that ballast layer with gray gravel with macropores could effectively prevent external heat flux reaching internal roadbed.The melting period of the ballast covered roadbed was 20 days shorter and the annual average ground temperature of the ballast covered roadbed at 5cm depth was 2.3 ℃lower than the roadbed without ballast,which showed good thermal insulation effect of the ballast layer.The wetting and evaporation effects of the ballast layer greatly reduced the infiltration of the surface precipitation into internal roadbed to keep relative stability of roadbed moisture.The results also indicated that subsurface moisture and temperature dynamics in the roadbed were strongly related to the rainfall events,while frequent and small rainfall events in summer led to a rapidly cooling of the subsurface soil and favored the thermal stability of the embankment.But there was no obvious water accumulation in the roadbed for rainfall evaporation.The effect depth of rainfall on the ground temperature and water content was less than 50 cm.