In order to study the cooling effect of the closed ballast layer on permafrost on the Tibetan Plateau,a test field with a closed ballast pit and a gravel surface was built near the Beiluhe test site of the Qinghai-Tibet Railway,and the ground temperatures beneath the test field have been monitored.

The railway ballast layer can be regarded as a highly porous medium,which has good ventilation characteristics.

Models and their extending on aggregating effect caused by the entrance and exit of closed corridor;

Depending on the structure of user cost and the influence of road blocked to the users, the user cost is assessed.