Study on design optimization of a crushed stone layer with shading board placed on a railway embankment on warm permafrost

Under the impact of potential climate warming and human engineering activities, the Embankment with Crushed Stone Slope Protection (ECSSP) needs further countermeasures to protect the underlying permafrost along the Qinghai–Tibet railway in warm (− 1 to 0 °C) permafrost regions according to the observed in situ data. In this paper, a new strengthening countermeasure, the Embankment with Shading Board and Crushed Stone Slope Protection (ESBCSSP), is proposed to cool the foundation soil and to protect the warm permafrost. The crushed stone layers placed on the side slopes of the embankment have an apparent “thermal semi-conductor” effect by intensive natural convection of pore air in the winter and a “heat shield” effect in the summer. The shading boards erected on crushed stone slope protection can shade the ground surface from the sun to lower its surface temperature, and can keep snow from covering the crushed stone layer in the winter, which can enhance the cooling effect of the crushed stone layer. Based on the processes of natural convective and conductive heat transfer in porous media, systemic numerical tests were performed to study the cooling effect of the ESBCSSP, and to propose the reasonable range in thickness, height and grain size of the crushed stone slope protection.