青藏铁路抛石护坡路基强迫对流特性数值分析

基于多孔介质中流体热对流的连续性方程、非达西流动量方程和能量方程，对强通风条件下青藏铁路典型抛石护坡路基内温度场和流速场的分布形态进行数值研究。研究结果表明，抛石护坡路基对多年冻土保护作用显著，抛石护坡路基的存在使夏季多年冻土上限明显提高，冬季抛石护坡路基下部土体回冻速度较天然地表下部土体更快，由于降温作用主要集中在护坡附近有限范围之内，对路基中部的降温作用相对较弱。整体而言，抛石护坡对冻土路基本体的保护作用有限，从长期降温效果来看，由于全球气候变暖的影响，强通风条件下抛石护坡路基中线以下土体的内部可能产生“似眼球状”融化夹层，不利于路基的稳定。迎风抛石护坡层中空气运动方向大致为沿护坡斜向上，背风抛石护坡层中空气运动方向以从下到上运动为主，抛石层内空气的运动形式为“绕流”，抛石层表面空气速度最大，内部较小，空气速度分布区间为1.24×10-3～12.8 m/s，数值结果与现场试验测得的风速区间基本一致。

Numerical analysis of forced convection characteristics of riprap slope embankment in Qinghai-Tibet railway

Based on the continuity, non-Darcy momentum and energy equations for fluid convection in porous media, the velocity and temperature fields of riprap slope embankments under strong ventilation condition were studied numerically in permafrost regions in the Qinghai-Tibet railway. The results show that the riprap slope embankments play a significant role in protecting the permafrost, under which the upper limit of permafrost increasing obviously in summer and the re-frozen process is much faster in winter compared to the permafrost under the native ground surface. The cooling effect of riprap slope embankment is limited mainly in the range of near slope embankment; so the centre of embankment can not be protected very well. With the climate warming, a thawing interlayer looks like an eyeball may be formed in the centre of permafrost under the riprap slope embankment, which is not conducive to the stability of slope embankment. The direction of air flow is from down to up along the slope in riprap slope at following wind side; but it is from up to down at counter wind side. The motion type of air flow in the riprap can be defined as roll flow; and the flow velocity is much larger at the surface of riprap than the inner. Besides, the distribution interval of velocity is between 1.24×10-3 m/s and 12.8 m/s; and the numerical result is mainly in accordance with the site test results.