Experimental study on influence of particle size on cooling effect of crushed-rock layer under closed and open tops

A series of Laboratory studies were carried out on the cooling effects of crushed rock layers with different particle sizes under closed and open tops. The thicknesses of crushed-rock layers are 130 cm and the mean particle sizes are 8.3 cm, 14.8 cm, 22.1 cm and 27.1 cm, respectively. The experimental results indicate that the cooling effects of the crushed-rock layers with open tops are less than those with closed tops under the same experimental conditions. Under closed top, the crushed-rock layers with different particle sizes have a similar cooling tendency and good cooling effects on the underlying soil layers; however, the cooling effect is best when the mean particle size is 22.1 cm. Under open top, the crushed-rock layers have some cooling effects and their bottom mean periodic temperatures are below 0 °C when their mean particle sizes are from 14.8 to 27.1 cm; however, the crushed-rock layer with mean particle size of 8.3 cm does not result in its bottom mean periodic temperature lower than the ambient temperature (about 0.5 °C) in the model box. The periodic temperature ranges at the bottoms of crushed-rock layers under open top are far larger than those under closed top. The particle size has little influence on the bottom periodic temperature range under closed top, however, the influence is more obvious under open top. Therefore, if the cooling characteristics of crushed-rock layers with different particle sizes under open and closed tops can be reasonably utilized in cold regions engineering, the underlying permafrost can be effectively protected and cost can been reduced.