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冰川冻土  2014 

混凝土的入模温度和水化热对青藏直流输电线路冻土桩基温度特性的影响

DOI: 10.7522/j.issn.1000-0240.2014.0098, PP. 818-827

Keywords: 青藏直流输电线路,多年冻土,桩基冻结融化,回冻时间,水化热

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Abstract:

施工过程中混凝土的入模温度和水化热对多年冻土区桩基施工期间的热稳定性具有重要影响.针对该问题,利用有限元方法定量研究了±400kV青藏直流输电线路冻土区锥柱基础入模温度、水化热和含冰量对桩基回冻过程、温度场变化和桩底融化深度的影响规律.结果表明水化热影响下,桩基中心温度在第3天达到最高,桩底滞后1d,基坑表面受其影响较小,主要受环境温度影响;第24天,桩底出现最大融化层,随着入模温度增加,融化层厚度相应增加,入模温度为6℃时融化层厚度为34cm,15℃时为55cm;入模温度越高,回冻时间越长,当入模温度为6℃时,完全回冻需经历52d,15℃时,回冻时间将增加7d.含冰量对桩底融化深度有影响,含冰量越大底部融化深度越小;冻土年平均地温是影响桩底融化深度的重要因素,少冰高温(-0.52℃)、低温(-1.5℃和-2.5℃)冻土条件下,最大融化层厚度分别为38cm、34cm和25cm.基于上述结果,在多年冻土地区的桩基工程,建议混凝土入模温度为6~8℃,底部碎石垫层至少40cm.

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