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摘要: 基于青藏公路冻土路基病害整治热棒试验工程, 建立热棒路基的等效传热模型, 运用有限元方法对其进行数值模拟, 研究青藏公路环境条件下热棒的工作周期、工作状态与作用半径, 并通过对试验工程2 a观测数据分析, 对比研究热棒在冻土路基中的降温效应。研究发现, 热棒在约为5个月的工作周期内并非连续工作而呈波动式, 实际工作时间为工作周期的2/3;热棒路基冬季降温效果明显, 有利于路基土体冷储量增加, 提高路基热稳定性; 热棒在路基中的降温强度, 水平方向随距离增大而衰减, 有效作用半径为2.25 m, 深度方向在热棒蒸发段最大, 降低上限附近季节融化层冻土热融敏感性。结果表明, 青藏公路热棒试验工程中其间距采用4.0 m是合理的, 路基双侧设置热棒优于单侧, 热棒向路基中心斜置更好。Abstract: Based on heat pipe test engineering for the frozen soil subgrade distresses treatment of Qinghai-Tibet highway, the equivalent model of heat transmission for heat pipe subgrade was established and simulated using finite element method, the working cycle, operating condition and operating radius of heat pipe were discussed under Qinghai-Tibet highway environmental conditions, the cooling effect of heat!pipe in permafrost subgrade was compared with the two-year observation data of the subgrade.Comparison results show that heat pipe work is not continuous but fluctuant in one work cycle about five months, its actual working time is two-thirds of one work cycle, the cooling effect of heat pipe subgrade in winter is obvious, which is good for the contained cool increase of soil body and improves subgrade heat stabilization, there is a decrease for its cooling strength with the increase of horizontal distance, its effective operating radius is 2.25 m, its maximum cooling strength is in evaporation segment in depth direction, which low the thaw sensitivity of permafrost in the seasonal thaw layer about permafrost table.The results indicate that the space between heat pipes for 4.0 m is reasonable, the installation positions of heat pipes at two sides are better than at one side, pile oblique placement is better than perpendicular placement.
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Key words:
- road engineering /
- heat pipe subgrade /
- numerical simulation /
- permafrost
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图 2 蒸发段与冷凝段的温差变化曲线
Figure 2. Temperature difference curve of evaporating segment and congealing segment
图 4 沿远离热棒方向温度梯度的变化
Figure 4. Relation of temperature and level distance from heat pipe
表 1 热棒几何及热学参数
Table 1. Geometry and thermal parameters of heat pipe
参数名称 值 热棒内径di/m 0.08 热棒外径do/m 0.10 蒸发段长度le/m 6.0 冷凝段长度lc/m 4.0 蒸发段内壁表面换热系数hi, e/[W·(m2·℃)-1] 5 000 冷凝段内壁表面换热系数hi, c/[W·(m2·℃)-1] 6 000 热棒管壁导热系数λ/[W·(m2·℃)-1] 10.0 翅片热传导的形状因子Sc 1.8 
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表 2 路基模型各层材料参数
Table 2. Material parameters of subgrade model
材料 砂砾与碎石土 含卵石中细砂 含砾亚粘土 强风化泥岩 干密度ρd/(kg·m-3) 1 800 1 700 1 300 1 500 初始含水量w0/% 25 30 30 30 融土骨架比热csu/[kJ·(kg·℃)-1] 0.79×103 0.84×103 0.84×103 0.84×103 冻土骨架比热csf/[kJ·(kg·℃)-1] 0.71×103 0.73×103 0.75×103 0.75×103 水的比热cw/[kJ·(kg·℃)-1] 4.182×103 4.182×103 4.182×103 4.182×103 冰的比热ci/[kJ·(kg·℃)-1] 2.09×103 2.09×103 2.09×103 2.09×103 融土导热系数λu/[W·(m2·℃)-1] 1.919 1.950 0.870 1.470 冻土导热系数λf/[W·(m2·℃)-1] 1.98 2.69 1.22 1.82 水分扩散系数D/(cm2·s-1) 9.35×10-6 4.66×10-5 3.73×10-4 3.44×10-6 冻结温度-θf/℃ -0.20 -0.10 -0.19 -0.05 水的冻结融化潜热L/(kJ·kg-1) 334.56×103 334.56×103 334.56×103 334.56×103 经验系数b 0.610 0 0.732 5 0.574 0 0.473 5
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表 3 地温曲线拟合参数及拟合度
Table 3. Polynomial fit parameters and covariances of ground temperature time curve
位置 参数 a0 b0 b1 a2 c0 拟合度(R) 地表大气 -4.73 10.77 2π/365 -7π/12 1.10×10-4 0.92 路中 +1.29 12.22 2π/365 -7π/12 1.10×10-4 0.90 路肩 -1.92 10.60 2π/365 -2π/3 1.10×10-4 0.94 天然地表 -4.00 8.55 2π/365 -2π/3 1.10×10-4 0.92 边坡 -4.00+208h/H 8.55+1.05h/H 2π/365 -2π/3 1.10×10-4 -
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表 4 热棒作用半径与温度
Table 4. Heat pipe operating radii and ground temperatures
距热棒水平距离/m 左路肩 右路肩 实测温度/℃ 回归计算值/℃ 实测温度/℃ 回归计算值/℃ 0.5 -1.46 -1.43 -2.65 -2.65 1.0 -0.96 -1.00 -2.04 -2.03 1.5 -0.59 -0.57 -1.42 -1.42 2.0 — -0.14 — -0.80 2.5 — 0.30 — -0.19
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