冻融循环下相变材料改良黄土路基物理力学特性研究

Physical and Mechanical Properties of Loess Subgrade Improved by Phase Change Materials under Freeze-thaw Cycles

冻融循环是影响路基黄土长期性能稳定的重要因素之一。为有效抑制冻融产生的不利影响,利用液体石蜡和相变微胶囊两种相变材料(Phase change materials, PCM)改良黄土。针对两种相变材料,各采用3种不同的配比制备试样,分别进行击实、无侧限抗压强度以及动三轴试验,并分析PCM配比、冻融循环次数对改良黄土物理力学特性的影响。研究结果表明,掺入液体石蜡的黄土最大干密度随掺量增加先上升后下降,最优含水率不断下降;掺入相变微胶囊的黄土最大干密度随掺量增加不断下降,最优含水率不断上升。另外,掺入PCM对黄土强度提升效果显著,其中掺入5%含量的相变微胶囊改良黄土强度提升最大,是天然土的2.9倍;掺入8%含量的液体石蜡改良黄土强度提升次之,是天然土的2.7倍。PCM改良黄土的动回弹模量值随围压增大而增大,随循环应力和冻融循环次数增加而不断下降,关系曲线均接近于线性。试验结果认为,采用相变材料和降低循环应力、提高围压可以降低冻融循环对结构的劣化作用。

Freezing-thawing cycle is one of the important factors affecting the long-term stability of subgrade loess. In order to effectively suppress the adverse effects caused by freezing-thawing, two phase change materials(PCM), the liquid paraffin and phase change microcapsule, are used to improve loess, and samples are prepared with three different ratios. Compaction, unconfined compressive strength and dynamic triaxial tests are respectively carried out. The effects of the ratio of PCM and the number of freezing-thawing cycles on the physical and mechanical properties of improved loess are analyzed. The results show that the maximum dry density of the loess mixed with liquid paraffin increases first and then decreases, and the optimal water content decreases continuously. The maximum dry density of the loess mixed with phase change microcapsules decreases with the dosage, and the optimal water content increases. Adding PCM has a significant improvement effect on loess strength, among which the improvement of loess strength by adding 5% phase change microcapsule is the biggest, which is 2.9 times that of natural soil, and the improvement of loess strength by adding 8% liquid paraffin is the second, which is 2.7 times that of natural soil. The dynamic rebound modulus of PCM improved loess increases with the increase of confining pressure, and decreases with the increase of cyclic stress and the number of freezing-thawing cycles. The relationship curves are close to linear. The results show that using PCM and decreasing cyclic stress or increasing confining pressure can reduce the deterioration of freezing-thawing cycle.