Abstract:

On the basis of in situ measurements, it is necessary that the embankment only with crushed rock protective slopes in the warm permafrost regions along the Qinghai-Tibet Railway needs proactive mitigative measures to maintain the long-term stability. Thus, an ad hoc technique of the crushed-rock protective slopes and the awning combination (CPS-AC) was proposed. The cooling effect and mechanisms of the CPS-AC were explored on the basis of previous studies on the individual mitigative measures of the awning and the crushed-rock protective slopes, and of the current studies on the temperatures and velocities of the CPS-AC embankment configurations. The CPS-AC is further divided into two types, the closed and open systems. In the closed system, the airs between in the ambient environment and under the awning can not exchange freely. In reverse, the airs can do freely in the open system. The awning in the closed CPS-AC can shade the direct solar radiation on the protective slopes and protect the embankments from blowing sands and snow, as well as winds; and the crushed rock layer in the closed CPS-AC has the “thermal semi-conductor” effect and can shade the secondary radiation from warm awning. In the open CPS-AC system, the shading board shades sunlight and obstructs snow, and the crushed rock layer can shield the secondary radiation of the warmer awning, and protect warmer winds from entering the embankment, and also has a chimney effect for cooling the embankment. The cooling effect of the open channel between the awning and the crushed rock slope can be explained using the siphon, channeling and chimney cooling effects. The measurements and research on the effects and mechanisms have provided important evidences and application techniques for the CPS-AC practices in the Qinghai-Tibet Railway.

Key words: warm permafrost, crushed-rock protective slopes and awning combination (CPS-AC), channeling, siphon and chimney effects, Qinghai-Tibet Railwaywarm permafrost, crushed-rock protective slopes and awning combination (CPS-AC), channeling, siphon and chimney effects, Qinghai-Tibet Railway