松铺覆盖下相变黏土施工防冻控温数值模拟

Numerical simulation on anti-freezing and temperature control of phasechange material in construction with loose-covering layer

堤坝及路基等工程冬季负温下施工,土料会因短时冻结或冻融而引起压实性能降低,并诱发冻胀、融沉、开裂等病害。常规覆盖保温措施工艺复杂,难以实现负温下连续施工,易使工期延长。相变黏土为改善土料防冻性能、延长冬季施工时间提供了可能,但相变材料(PCM)掺量过高影响土料力学性能。为此,本文提出了土料掺混PCM与松铺覆盖联合的防冻控温措施,利用原有施工中上层土料松铺工序,尽可能减少PCM掺量,减小施工干扰,同时解决负温施工暴露时段土料的表层防冻问题。首先,建立了考虑上层土料松铺的施工相变传热有限元数值模型,并验证了模型的有效性;然后,定量分析了不同松铺厚度、PCM掺量对相变黏土冬季施工控温效果的影响,提出了相变黏土有效施工时长的估计方法;最后,给出了防冻控温措施建议,采用2%PCM掺量和9.6 cm松铺覆盖层厚度,即可满足现场施工控温的要求。本研究为解决寒区土料冬季施工过程中的防冻控温难题提供了新的技术途径。

During the construction of embankment and subgrade under negative temperature in winter,the compaction performance of the materials will be reduced due to short-term freezing or freezing-thaw,which will lead to frost heave,thaw collapse,cracking and other diseases.The process of conventional covering insulation measure is complex,which makes it difficult to achieve continuous construction in negative temperature,and likely to extend the construction period.Phase change materials(PCM)provide possibility to improve the frost resistance and ensure the construction time in winter.However,the high content of PCM affects the mechanical properties of soil.Therefore,the paper proposed a combined anti-freezing and temperature control measure of mixing PCM and loose-covering.Using the original upper loose-covering process in the construction,reduced the PCM content and the construction interference as much as possible,and solved the surface anti-freezing problem of the soil during the negative temperature construction exposure period.First,a finite element numerical model of construction phase change heat transfer considering the upper loose-covering was established,and the validity of the model was verified.Then,the influence of different loose-covering thickness and PCM content on the temperature control effect of PCM in winter construction was quantitatively analyzed,and the estimation method of effective construction time of PCM was proposed.Finally,the suggestion of anti-freezing and temperature control measures was given.The 2%PCM content and 9.6 cm loose-covering thickness can meet the requirements of temperature control.This study provides a new technical way to solve the anti-freezing and temperature control problem during the construction in cold regions in winter.