基于热棒功率变化下多年冻土区输电塔热棒桩基的长期降温效果预测

Prediction of long-term cooling effect of thermal pipe foundation of transmission tower in permafrost regions considering the change of thermal pipe power

青藏铁路建设中输电塔穿越多年冻土地区,最大的难题是解决输电塔桩基的长期热稳定性问题。为研究热棒应用于输电塔桩基的长期降温效果,基于冻土传热学相关知识,考虑全球气候变暖、冻土相变、混凝土水化放热、热棒功率变化等因素,结合青藏铁路望昆—不冻泉段电力塔热棒桩基的现场试验,建立热棒桩基的三维有限元模型。计算分析50 a内热棒功率和桩土体系温度场。计算结果表明:最初2 a内的计算值与实测值吻合度较高,说明数值计算能较好的模拟此场地桩土体系温度的动态变化;在热棒的全寿命周期30 a内,热棒功率呈非连续波浪递减式变化;热棒桩基能有效增加冷储量,降低土体地温,第5年桩周土体地温降至最低,融化深度最小,第30年可提高冻土上限48cm;建议在热棒寿命结束后的第2年更换新的热棒或进行其他工程处理措施保持输电塔基础的热稳定。

For power transmission towers along Qinghai—Tibet railway line which rans across permafrost regions,the biggest problem is to solve the long-term thermal stability of transmission tower pile foundation.In order to study the long-term cooling effect of thermal pipes applied to the pile foundation of transmission towers,a three-dimensional finite element analysis model of thermal pipe foundation was established based on frozen soil heat transfer theory and field test of thermal pipe foundation of power tower in the Wonkhu—Budongquan section of Qinghai—Tibet railway and considering global warming,frozen soil phase change,hydration heat release of concrete and change of thermal pipe power factors,et al.The power of thermal pipes and the temperature of the pile-soil system in 50 years were calculated and analyzed.The calculation results show that,in the first two years,the calculated and measured values are in good agreement with each other,which indicates that the proposed model can reasonably simulate the dynamic change of the temperature of the pile-soil system in this site.Within 30 years of the whole life cycle of the thermal pipe,the power of the thermal pipe decreases in a discontinuous wave form.The thermal pile foundation can effectively increase the cold reserve of the foundation and reduce the soil temperature.In the fifth year,the soil temperature around the pile is the lowest and the melting depth is the least.The thermal pile foundation can increase the permafrost upper table by 48 cm in the thirtieth year.In order to maintain the thermal stability of the transmission tower foundation,it is recommended that thermal pipes are replaced by new ones or that other engineering measures are adopted in the second year after the end of the life of the thermal pipes.