Enhancement of convective cooling of the porous crushed-rock layer in cold regions based on experimental investigations

Abstract

A crushed-rock layer, because of its pore-air convective cooling effect, has been widely used to adjust the geotemperature of the permafrost stratum in cold regions. To optimize the control measure, a series of experiments have been conducted. The convective heat transfer capability of crushed-rock layers with different thicknesses is evaluated. The experimental results indicate that: 1) forced convection occurs during warm period and mixed convection occurs during cold period. The cooling performance is mainly determined by the forced convective heat transfer process; 2) pore-air flow pattern can change thermal resistance of the crushed-rock layer. Larger thermal resistance can reduce heat accumulation during the warm period and smaller thermal resistance can strengthen heat transfer during the cold period; and 3) there exists an optimal thickness to enhance the convective cooling effect. Under the experimental conditions, the optimum thickness is close to 1.3m. These findings are helpful to the construction of cold regions engineering. If the thickness of crushed rock revetment could be reasonably designed, the well convective cooling effect can be achieved and the construction costs will also be reduced.