一种冻土地基冷却承载复合桩的冷却机理分析及效果

COOLING MECHANISM ANALYSIS AND COOLING EFFECT EVALUATION FOR A NEW TYPE OF PILE USED IN FROZEN SOIL FOUNDATION

针对多年冻土地区桩基普遍存在的冻胀和热扩散问题,基于“主动冷却”地基的思想,结合碎石路基、碎石堆等大孔隙多孔介质在气温波动条件下具有的热二极管的效应,提出了一种用于冻土地区的新型桩;在冻融活动层深度范围的桩身表面刻制凹槽,利用槽内回填的碎石、块石等大孔隙多孔介质在外界大气温度自然波动下的对流换热机制,来达到主动冷却冻土和抬升冻土上限的目的;对其冷却机理及可行性进行了研究,运用数值仿真试验对比了桩身刻槽前后的温度场。结果表明,新型桩促进了冻土的发育,回冻时间大为缩短,冻土上限抬升。

Based on the idea of active cooling, aiming at problems of frozen heaving and heat diffusion which commonly exist in frozen soil pile foundation, a new type of pile is proposed to overcome the disadvantages of the classical pile used in frozen soil. Pile body within active layer is fluted and refilled with porous materials such as gravels and ballasts. Thus convections occur and thermal exchanges inside porous materials in winter, but heat conduction exists only in summer because cold air is at the bottom of the fluting. As a result, the soil around flutings is cooled and the permafrost tables are raised. This paper analyses the cooling mechanism and feasibility and the temperature field of classical pile, and the new type of pile by numerical simulation. The results of numerical simulation indicate that the new type of pile can promote permafrost growth, accelerate the course of refreezing greatly after fluting via effect of natural convection for dropping temperature, help raising the permafrost table, and consequently enhance pile bearing capacity and its capability for resisting frost heaving and thaw settlement.