青藏公路热棒路基降温效能
Cooling effect of thermosyhpon subgrade for Qinghai-Tibet Highway

为了分析多年冻土区热棒路基的工程效果,定量评价其降温效能,基于青藏公路热棒路基试验工程近11年的现场监测数据,分析了热棒路基的地温特征、温度场形态和冻融过程,估算了阴阳坡影响下热棒附近的水平热收支状况。建立了空气-热棒-冻土地基三维非稳态耦合计算模型,分析了不同结构形式(单侧直插式、单侧斜插式、双侧直插式与双侧斜插式)的热棒路基的降温效能。实测结果表明:在热棒作用下,阳坡侧路基地温可降到-1.5 ℃附近,较普通路基地温降低约3.0 ℃,阴坡侧路基地温最低达到-2.1 ℃; 热棒路基经过11年的营运,阳坡侧冻土上限抬升约0.95 m,基本达到天然地基水平; 阴阳坡两侧热棒的年平均实际功率分别约为69.80、54.07 W,且热棒路基在最初5年传递能量较大,第6年后逐渐减小,此后路基的热状况进入相对稳定的状态。计算结果表明:双侧直插式热棒路基与双侧斜插式热棒路基第20年冻土上限分别为2.88、1.88 m,而单侧直插式热棒路基与单侧斜插式热棒路基第20年冻土上限分别为3.84、3.46 m,因此,双侧热棒路基的长期降温效果明显强于单侧热棒路基,斜插式热棒路基强于直插式热棒路基; 单根热棒的年平均功率为47～56 W,与试验工程监测结果较为吻合。
In order to analyze the engineering effect of thermosyphon subgrade in permafrost regions and quantitatively evaluate its cooling effect, the 11 years’ observational data were collected from the thermosyphon subgrade test project of Qinghai-Tibet Highway, the ground temperature characteristics, temperature field profiles and freezing-thawing process of thermosyphon subgrade were analyzed, and the horizontal thermal budget near the thermosyphons under the influence of shady-sunny slope effect was evaluated. A three-dimensional unsteady coupled air-thermosyphon-foundation computation model was proposed, and the cooling effects of thermosyphon subgrades with different structures, such as one-side vertical type, one-side inclined type, two-side vertical type and two-side inclined type, were investigated. Measured result shows that the monitoring data indicates that the ground temperature of thermosyphon subgrade at sunny side is about -1.5 ℃, 3.0 ℃ lower than the value of traditional subgrade, and the lowest ground temperature at shady side can reach to -2.1 ℃. During 11 years’ operation of thermosyphon subgrade, the permafrost table at sunny side elevates about 0.95 m, and basically reaches to the level of natural foundation. The mean annual actual powers of thermosyphon subgrades at shady side and sunny side are about 69.80 and 54.07 W, respectively. During the previous 5 years, the thermosyphon presents a larger power. After 6th year, the power gradually decreases, and the thermal state of subgrade tends towards stability. Calculated result shows that after 20 years, the permafrost tables under the two-side vertical and inclined type thermosyphon subgrades are 2.88 and 1.88 m respectively, the permafrost tables under one-side vertical and inclined type thermosyphon subgrades are 3.84 and 3.46 m, respectively, so, the two-side type thermosyphon subgrade expresses a stronger long-term cooling effect than the one-side type thermosyphon subgrade, similarly, the inclined type thermosyphon subgrade has a stronger cooling effect than