Developing features of thaw grooves and their influence on stability of roadbed along Qinghai-Tibet Railway

Thaw grooves are common features of ice-rich permafrost landscapes, whose own settlement and lateral thermal erosion will do damage to the engineering infrastructures. With the persistent climatic warming and the influences of steadily increasing human activities, the harmfulness of the thaw grooves to frozen soil roadbed will be one of the important problems of the prevention and treatment to the frozen roadbed defects. In this study a representative thaw groove at the west side of Qinghai-Tibet Railway at K980+000 Mileage is taken as an example to monitor the changes in ground temperatures and the deformation. Integrated analysis on the monitoring results indicates that the thaw groove in bottom subsides about 15 cm within two years (2007 to 2008), and the average velocity is close to 8 cm. a-1. The warm season is the main period of settlement, especially from August to October. The upper layers soils at both shoulders of the thaw groove gradually glide inward the groove, and the horizontal displacement at depth of 0.5 m is about 5 cm·a-1. The mean annual ground temperature in the thaw groove is about 0.5℃ higher than that in undisturbed regions. For thermal regime of the thaw groove, the absorbing heat starts in mid April, ends in the beginning of November, and lasts about 233 days. The approximate calculation shows that the absorbing heat per unit area is about 3300 kJ per year, and about 70000 kJ heat is transported from the thaw groove to frozen soil roadbed per year. It would result in permafrost warming and decline of stability.