心墙相变砾质土工程特性及寒区冬季施工防冻控温研究

Engineering characteristics and temperature control of phase change material and gravel mixed soil for core wall anti-freezing

寒区砾质土心墙堆石坝冬季施工面临着心墙土料冻结与融化问题。通常冬季心墙填筑采用摊铺保温材料以防止土料冻结,但易干扰施工,导致有效填筑时间缩短。本文利用相变材料(Phase Change Material, PCM)的相变储放热性能,制备了心墙相变砾质土,用于寒区冬季砾质土心墙控温防冻。通过渗透试验、无侧限抗压试验、三轴试验、热常数试验及温控试验等,研究不同PCM掺量下心墙相变砾质土工程特性和防冻控温性能。试验结果发现,相变砾质土的无侧限抗压强度、抗剪强度和抗渗性能均随PCM掺量的增加而显著提高;随着PCM掺量的增加,相变砾质土导热系数及比热下降。在室内控温箱试验验证相变传热模型有效性的基础上,开展了心墙相变砾质土施工控温有限元模拟,分析了不同施工环境温度(最低温-5℃、-8℃和-10℃)工况下心墙相变砾质土的温控效果,发现6%PCM掺量的相变砾质土在最低温-5℃施工环境下保证土体不发生冻结;采用提高制备温度和上层铺筑联合控温措施,可保证最低温-10℃施工环境下心墙连续高效填筑;与常规砾质土相比,相变砾质土可延长心墙冬季施工时间,改善了心墙砾质土防冻性能,为心墙土料冬季施工防冻提供了一种潜在选择。

Core-wall construction of a gravelly soil rockfill dam in cold region usually faces the freeze-thaw challenge.In current practice, it is common to cover soil with thermal insulation material to prevent core wall from freezing.However, the release and reclaim process of thermal insulation material easily interfere the core-wall compaction process, which would reduce the effective construction time.Based on the heat storage/release property of phase change material(PCM),this paper developed a phase change material incorporated into gravelly soil(PCM-GS) to improve the anti-freezing performance in a cold period.The engineering characteristics and anti-freezing performance of PCM-GS was analyzed through permeability, unconfined compression, triaxial compression, hot disk and temperature control tests.The results indicate that the unconfined compressive strength, shear strength and impermeability of PCM-GS are significantly higher than those of the gravelly soil without PCM.The thermal conductivity and specific heat of PCM-GS decrease with PCM content.According to the temperature control test, a finite element simulation model of heat transfer with PCM-GS was verified under core-wall construction conditions.The anti-freezing performance of PCM-GS during winter construction was analyzed under different ambient air temperatures(minimum temperatures are-5 ℃,-8 ℃ and-10 ℃,respectively).The simulation result shows that the PCM-GS at 6% PCM content is able to prevent soil from freezing when the minimum ambient temperature is-5 ℃.The combination of increasing the initial temperature of PCM-GS and covering an upper layer assures the continuous core-wall construction with high efficiency when minimum ambient temperature is-10 ℃.Compared with gravelly soil without PCM,the PCM-GS extend the construction time for core-wall compaction in winter, which offers a potential alternative to improve the anti-freezing performance of PCM-GS during winter construction.