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针对青藏直流联网工程塔基热管措施应用效果,通过现场实测资料确定了热管年内工作周期及混凝土桩基表面热效应,考虑无绝热段热管传热过程组成,建立空气–热管–土体耦合传热数学模型,利用有限元方法系统模拟不同年平均地温分区锥柱式塔基传热过程及气候变暖背景下基础周围多年冻土热状况发展变化趋势。结果表明:冷季热管工作期间,其对周围土体冷却降温效果显著,同时由于混凝土塔基为热的良导体,热管产生的“冷量”通过基础及其底座快速向基础周围传递,使得基础下形成大范围低温冻土。暖季,热管停止工作期间,由于基础埋设较浅,混凝土塔基良好的导热性能使得其周围浅层土体温度升温较快,量值基本与天然地表下同一深度接近,而基础下部深层地温则主要受热管作用控制,温度较低。在单一塔腿4根热管及50 a气温升高2.6℃背景下,-1.0℃、-1.5℃两种年平均地温条件下,桩基础下部多年冻土仍保持冻结状态,满足工程对于冻土地基热状况的要求。-0.5℃年平均地温条件下,运营后期桩基础周围土体季节融化深度已大于桩基埋深。在该地温条件下,通过热管–保温板复合措施的采用,可有效发挥热管的“冷却降温”及保温板的“隔热保冷”效能,在大幅减小基础周围土体的最大季节融化深度的同时降低锥柱式基础底部深层地温,进而满足工程需求。
In view of the application effect of tower-based heat pipe measures in Qinghai-Tibet DC network project, the work cycle of the heat pipe during the year and the surface thermal effect of concrete pile foundation are determined through on-site measurement data. Considering the composition of heat pipe heat transfer without insulation, the air- Model, the finite element method was used to simulate the heat transfer process of pyramidal column foundation with different annual average geothermal subzones and the development trend of permafrost thermal conditions around the foundation under the background of climate warming. The results show that during cold season heat pipe cooling, the cooling effect on the surrounding soil is remarkable. At the same time, because the concrete tower base is a good conductor of heat, the “cold capacity” produced by the heat pipe is quickly transferred to the base around the base through the base and base, Based on the formation of a wide range of low temperature permafrost. During the warm season and during the shutdown of the heat pipe, due to the shallow foundation, the good thermal conductivity of the concrete tower makes the temperature of the shallow soil around the furnace rise rapidly, and the basic value is close to the same depth under the natural subsurface, while the deep ground temperature Mainly by the role of heat pipe control, the temperature is low. The permafrost in the lower part of the pile foundation remains frozen under the condition of 4 heat pipes with single tower leg and air temperature rise of 2.6 ℃ in 50 a, -1.0 ℃ and -1.5 ℃, and meets the requirement of engineering for frozen soil foundation Thermal requirements. Under the mean annual temperature of -0.5 ℃, the seasonal thawing depth of the soil around pile foundation in the late stage of operation is greater than that of pile foundation. Under the condition of the geothermal temperature, the heat pipe - insulation board composite measures can effectively play the “cooling and cooling” of the heat pipe and the “insulation and cold protection” performance of the heat insulation board, so as to greatly reduce the maximum soil mass around the foundation The seasonal melting depth reduces the deep ground temperature at the base of the cone-column foundation to meet the engineering needs.