Disturbance-related thawing of a ditch and its influence on roadbeds on permafrost

A thawing ditch existing in permafrost region along the Qinghai–Tibet Railway is studied with their geological features, failure characteristics, ground temperatures, and influence on permafrost roadbed in this paper. The failure shows surface subsidence and horizontal slip on the shoulder. Integrated analysis from the field-monitored data show that the thawing ditch totally subsided more than 11 cm from January 2008 to (month) 2010 and the average was close to 6 cm a−1. The active layer on both shoulders of the thawing ditch has been slipped inward, and the max horizontal displacement in 0.5 m depth was 5–6 cm a−1. The warm season is the main period of the failure expanding in scale, especially from August to October. The mean annual ground temperature in shallow layer was about 0.9 °C higher in the thawing ditch bottom than in the natural ground (remove about 20 m) during the past two years (2008–2009). Due to the vegetation covered on the thawing ditch was destroyed, and the heat absorbed exceeds obviously heat released. The estimated result using the data in 2008 and 2009 shows that the input of heat into the permafrost below the thawing ditch was about 114,000 kJ m−2 and was more than the output of 88,000 kJ m−2 in two years. The heat absorbing starts in mid April, ends at the beginning of November, and lasts over 230 days. In addition, the lateral thermal erosion of thawing ditch would influence the surrounding permafrost and damage the adjacent engineering infrastructure. The approximate calculation shows that about 90,000 kJ heat was transported from thawing ditch to adjacent permafrost in 2009. Therefore, the permafrost beneath the thawing ditch has been degrading, warming, and declining in stability.