Laboratory investigation on cooling effect of coarse rock layer and fine rock layer in permafrost regions

Instability and failures of railway/roadway embankment are mainly caused by thaw settlement of permafrost in cold regions. To protect foundation soils beneath the embankment from thaw settlement is the primary construction principle. In the present study, the heat transfer characteristics of two cases of porous media were examined experimentally, with periodic temperature boundary at the top surface of models, while the bottom and sides were impermeable and insulated. Wind velocity over the model top kept a constant. Case 1 was coarse rock layer, with mean particle size 22 cm. Case 2 was fine rock layer (mean particle size 7 cm). The results for both cases are analyzed and compared. Results show that both the two cases have cooling effects. They can cool the soil underlying them. The cooling effect of Case 2 is better than that of Case 1. At the end of the test, temperature at the bottom of Case 2 is 3.5 degreesC colder that of Case 1. At the end of the negative and positive temperature stages, temperatures within coarse rock layer change monotonously from top to bottom, but it is no-monotonously within fine rock layer. The temperature of rock particle surface is warmer than the pore-air temperature in coarse rock layer during the positive temperature stage. A critical thickness for rock layer is necessary if they can yield cooling effects. The cooling characteristics of rock layer can be used to prevent embankment from thawing settlement and forming longitudinal cracks in permafrost regions. (C) 2004 Elsevier B.V. All rights reserved.