松铺覆盖下心墙相变土防冻控温性能试验研究

Investigation on anti-freezing performance of core wall phase change material-incorporated clay with an upper loose-covering layer

高黏土心墙堆石坝在负温条件下施工,心墙土料会因短时冻结或冻融而引起压实性能降低,诱发冻胀、融沉、开裂等结构病害,造成强度损失和防渗性能的劣化。常规覆盖保温措施对心墙施工干扰严重,难以实现负温下连续施工,易使工期延长。本文采用黏土中掺入相变材料(phase change material,PCM)作为心墙土料,考虑上层松铺土料覆盖,深入研究下层压实相变黏土料的防冻控温效果。首先通过热学试验,分析了PCM掺量对热学参数的影响机制,并验证了导热系数均质化等效模型的有效性。然后通过控温试验,分析了松铺相变黏土的传热及保温效果。在48 h典型环境温度下,松铺覆盖下4%和8%PCM掺量的相变黏土可施工时间分别延长了22.6 h和24.9 h,在4%PCM掺量下能够达到45.8 h的连续有效施工时长,在8%PCM掺量下可保证连续两天正温下施工。可见,相变材料掺混和上层松铺覆盖结合的防冻控温措施为延长心墙土料冬季施工时间、加快施工进度提供了理论依据和潜在技术途径。

For construction of a high core-wall clay earth-rock dam at negative air temperature,it is common to see compactability degeneration and structural defects(e.g.frost heave,thawing settlement and structure crack)after short-term frozen or freeze-thaw cycles,leading to working performance deterioration in strength and impermeability.Conventional measures,e.g.covering thermal insulations,interfere severely with corewall clay paving and filling,and suffer difficulty in maintaining continuous construction.In this work,a phase change material-incorporated clay(PCM-clay)is used as core wall material;anti-freezing performances of the lower PCM-clay are investigated considering the effect of an upper loose-covering layer.We analyze the impact of PCM content on thermal characteristics,and verify the effectiveness of a homogenization model for thermal conductivity through thermal tests.Then,heat transfer and thermal performance of the upper layer is examined by conducting thermal cycling tests.Under 48-hour typical temperature,construction time extension for the core wall clay with 4%and 8%PCM contents are 22.6 and 24.9 hours,respectively.For 4%PCM-clay,the total continuous construction time in 2 days is 45.8 hours;8%PCM-clay even keeps above positive temperature for 48 hours.The results indicate that the anti-freezing measures of PCM-clay and upper loose covering provide a theoretical basis and potential way to extend winter construction time,thus helping accelerate the construction progress of core walls in cold regions.