季节性冻融对滞洪区改良路基性能的影响

Performance of improved soil subgrade under freeze-thaw cycles in flood retarding basin

针对苏北黄泛区粉土路基受季节性冻融的影响,对水泥、石灰、粉煤灰不同组合的12种粉土路基改良填料开展冻融环境下抗压强度、质量损失（抗冲刷能力）的试验研究,分析不同组分下改良土的抗冻性能。结果表明,随着冻融循环次数的增加,粉质土抗压性能及质量完整性逐步衰减,衰减过程具有明显的阶段性。水泥粉煤灰改良土的抗冻效果明显优于水泥石灰组合,水泥石灰改良土在冻融循环后由于材料脆性变强而使得填料更易崩解。在各组分对冻融破损的抑制方面,水泥的胶结作用显著,在水泥质量分数为2%-7%时,可以抑制冻融导致的强度衰减,提升抗冲刷能力;石灰能一定程度改善填料抗冻性,但由于其自身的膨胀性又对质量损失控制、抗冲刷能力存在不利影响;而粉煤灰的添加却可以在抑制强度衰减尤其保持质量完整性方面发挥着重要的作用。添加5%水泥及15%粉煤灰的改良组合可使苏北黄泛区季节性冻融环境下粉土路基具有较优异的抗冻性能。

In order to study the performance of the improved soil subgrade in the Yellow River flood retarding basin in northern Jiangsu Province,twelve series of samples of the improved soil subgrade were prepared by mixing cement,lime and fly ash with designed proportions,and then subjected to designated freezing-thawing（ FT） cycles. Thereafter,the properties of compression strength and mass loss（ anti-erosion） of the samples were examined. Research results showed that the compression strength and integrity of the subgrades decreased with the increase in FT cycles,and the decrease rate was obviously dependent upon the different stages during those cycles. The cement and fly ash mixture was superior to the cement and lime mixture under freeze-thaw cycles,because the soil subgrade modified with cement / lime became brittle and could be easily disintegrated. In term of individual modifier,cement can improve cohesion significantly. At an incorporation content between 2% and 7%,the cement can delay the decrease of compression strength and enhance erosion resistance of the subgrade. Lime could improve the resistance to freeze and thaw to certain extent,but may contribute to mass loss and soil erosion due to its thermal expansion nature. Similar to cement,fly ash can also delay strength decrease and maintain the integrity of soil subgrade. This study investigated the influence of different modifier on the properties of compression strength and mass loss,suggesting that the optimum mixture was 5% cement and 15% fly ash.The result can be applied to the flood retarding basin for enhancing the subgrade properties under freeze-thaw cycles.