Numerical study on the influence of geometrical parameters on natural convection cooling effect of the crushed-rock revetment

Abstract

The crushed-rock revetment, considered as a highly porous medium, is often applied to embankment slope to protect the underlying permafrost and ensure the thermal stability of roadway in permafrost regions. In this paper, in order to increase and optimize the cooling capacity of crushed-rock revetment in cold regions roadway engineering, based on the thermal convection theories, the practical geometry and the temperature characteristics of in-situ crushed-rock revetment, convective pattern and cooling effect of crushed-rock revetment are numerically studied, with a thickness of 1.0 m under different geometrical parameters, e.g. sloped angle and aspect ratio. The results indicate that, with a thickness of 1.0 m and a temperature difference of 10.0 °C between top and bottom boundaries, due to the existence of natural convection, the effective thermal conductivity of crushed-rock revetment can be increased and the thermal “semi-conductor” characteristics are endowed. However, the convective pattern changes with the variation of the sloped angle, namely, with the increase of the sloped angle, the convection cell number decreases; furthermore, when the flow changes from various cells to a single cell at a sloped angle, the Nu number is the smallest and the cooling effect is the worst, therefore, the corresponding sloped angle is considered as the worst cooling sloped angle. Besides, with the increase of the aspect ratio, the worst cooling sloped angle increases and tends to 32°, also approaching to the in-situ crushed-rock revetment angle 33.7°. Therefore, when the crushed-rock revetment embankment is too high, that is to say, the aspect ratio of the sloped crushed-rock revetment is too large, some measures should be taken to enhance its cooling effect, which have been researched and discussed in this paper. It is hoped that some scientific references can be supplied to the design and maintenance of the crushed-rock revetment embankment in cold regions.