【正文】 he other is crushedrock cutting structure with insulation only embedded at the side slopes and crushed rock filled at the bottom, which is regarded as a proactive measure. The numerical results show that, when the cutting has to be constructed in warm permafrost regions or in degenerating cold permafrost regions, if the ice content is low in the underlying permafrost, the insulated cutting structure can be used, however, if the ice content is high, the crushedrock cutting structure can be an effective approach to protect the underlying permafrost and has a better longterm thermal stability. Key words: aircooled subgrade。在理論上，揭示了氣冷路基的降溫機(jī)理，提出了新的計(jì)算方法和數(shù)學(xué)模型；在應(yīng)用上，針對(duì)寒區(qū)重大工程中的關(guān)鍵科學(xué)技術(shù)問(wèn)題，提出了有效的解決方法，成果已在青藏鐵路工程中得到應(yīng)用并取得良好效果。 多年凍土區(qū)路堤中的塊碎石層多處于開放狀態(tài)，其內(nèi)部對(duì)流換熱模式直接受到外界風(fēng)的作用。 運(yùn)用本模型對(duì)青藏鐵路多年凍土區(qū)封閉塊碎石路堤的速度場(chǎng)及未來(lái) 50 年的溫度場(chǎng)進(jìn)行了預(yù)測(cè)分析。為此，提出了一種“ U 形塊碎石路堤”結(jié)構(gòu)。數(shù)值研究結(jié)果表明，在高溫多年凍土區(qū)或退化型低溫多年凍土區(qū)進(jìn)行挖方，當(dāng)下部多年凍土含冰量較低時(shí)，可以考慮使用保溫路塹結(jié)構(gòu)，但當(dāng)含冰量較高時(shí)，塊碎石換填路塹可以作為一種能夠有效保護(hù)下部多年凍土的結(jié) 構(gòu)形式，并具有較好的長(zhǎng)期熱穩(wěn)定性。 6. 提出了在路塹基底換填塊碎石的新方法，為確保高溫、高含冰量多年凍土區(qū)路塹的長(zhǎng)期熱穩(wěn)定性提供了新的技術(shù)措施。本模型解決了通風(fēng)管內(nèi)外空氣的對(duì)流換熱以及管內(nèi)空氣與管壁間的耦合傳熱計(jì)算問(wèn)題。但由于主導(dǎo)風(fēng)向的影響，較高路堤下溫度場(chǎng)會(huì)出現(xiàn)較嚴(yán)重的橫向不對(duì)稱問(wèn)題，而較低路堤則無(wú)此現(xiàn)象發(fā)生； 3) 開放塊碎石護(hù)坡路堤降溫效果主要集中在坡腳，路堤中部相對(duì)較弱，長(zhǎng)期熱穩(wěn)定性相對(duì)較差。 研究結(jié)果表明，在風(fēng)的作用下，邊界狀態(tài)對(duì)塊碎石層降溫效果和降溫機(jī)理有著決定性的影響：封閉邊界的塊碎石層，當(dāng)滿足一定條件時(shí)內(nèi)部有自然對(duì)流發(fā)生，具有明顯的熱半導(dǎo)體特性；而開放塊碎石層的熱量傳遞主要是依靠強(qiáng)迫對(duì)流，熱半導(dǎo)體特性不顯著。而通過(guò)采取有效工程措施保護(hù)多年凍土，避免凍土路基的融沉，確保道 路的 長(zhǎng)期穩(wěn)定，正是解決這一關(guān)鍵凍土問(wèn)題的有效途徑，也是多年凍土區(qū)道路工程建設(shè)中最為重要和復(fù)雜的關(guān)鍵科學(xué)技術(shù)問(wèn)題之一。 and 3) the cooling effect of open crushedrock revetment embankment is strongest at the sideslope foots and relatively weak in the middle, so that its longterm thermal stability cannot be well ． The convective heat transfer mathematical model for closed crushedrock embankments in permafrost regions was established to study the heat transfer characteristics and cooling effects of crushedrock embankments under special closed of the plicated conditions in field, the open crushedrock embankment is often covered by sand, snow and so on, or plugged by human, so that a special closed system can be formed in the crushedrock layer. Due to different boundaries, the convective heat transfer pattern within the closed structure is distinctly different from that within the open one. Therefore, to research the heat transfer characteristics of crushedrock embankment under the special closed conditions, based on the nonDarcy flow theory in porous media, the convective heat transfer model for closed crushedrock embankments in permafrost regions was established, and verified by laboratory investigation. Using the above model, we numerically forecasted the velocity and temperature distributions of closed crushedrock embankments in permafrost regions along the QinghaiTibet Railway for the next 50 years. The results show that, the cooling effect of closed crushedrock embankments is from natural convection。 however, on the leeward side, when the ambient air temperature is lower, the heat transfer mechanism is more plicated and natural convective effects occur. Furthermore, the cooling effect is greatest when the particle size is 2123 cm. 2． The calculational methods for the velocity and temperature fields of open crushedrock embankments were presented under outside wind action in permafrost regions. Thus the problem for puting fluidsolid coupled heat transfer of crushedrock embankment was solved in the QinghaiTibet crushedrock layer,