水泥固化重金属污染土干湿循环特性试验研究

水泥固化/稳定法是修复污染土地基的常用方法，修复后的固化土在外界环境干湿循环作用下的稳定性如何是事关修复成败的关键所在。通过系统的室内试验，着重研究了水泥固化Pb²⁺、Zn²⁺污染土在干湿循环作用下的强度特性、淋滤特性以及微结构变化规律，揭示了水泥固化重金属污染土的微观作用机制。试验结果表明，固化土体的强度及淋滤特性随着水泥掺量的增加得到了显著改善。固化重金属污染土的无侧限抗压强度随干湿循环次数的增加先增大，达到峰值后，随干湿循环次数的继续增大而减小。污染物掺量较低时，重金属离子的滤出浓度在干湿循环作用初期略有降低，此后则有所增加，但变化幅度较小；高污染物掺量时，滤出液中的重金属离子浓度较高，且随着干湿循环次数的增加而不断增大。低污染物掺量下，水泥对Pb²⁺及Zn²⁺固化效果相差不大；高污染物掺量下，水泥对Zn²⁺的固化效果较好。经过干湿循环作用后的固化土的扫描电镜试验结果与与其宏观力学及淋滤特性指标变化规律一致，从微观角度揭示了固化土工程性质的变化机制。

Cyclic wetting and drying tests on heavy metal contaminated soils solidified/stabilized by cement

Cement solidification/stabilization is a commonly-used method for the remediation of contaminated soils. The stability characteristics of solidified/stabilized contaminated soils under wetting and drying cycles are very important. A series of test programs, unconfined compressive strength (UCS) tests, leaching tests and scanning electron microscopy (SEM) tests are performed to study the long-term stability of solidified/stabilized lead and zinc contaminated soils with cement under cyclic wetting and drying. The test results show that UCS and the leaching characteristics of heavy metal ions of stabilized contaminated soils are significantly improved with the increase of the cement content. UCS of stabilized soils first increases with the increase of times of wetting and drying cycle, and after reaching the peak, it decreases with the increase of times of wetting and drying cycle. When the pollutant content is lower (1000 mg/kg), the leaching of heavy metal ions first slightly decreases under cyclic wetting and drying, then increases, but the change is minor. The concentration of heavy metal ions in the filtrate of the stabilized contaminated soils is higher under a high pollutant content of 5000 mg/kg, and increases with the increase of times of wetting and drying cycle. It exhibits a similar effect of the solidification/stabilization of lead and zinc contaminated soils using cement under a lower pollutant content. Compared with the lead contaminated soils, the zinc contaminated soils can be better stabilized with cement when the pollutant content is higher (5000 mg/kg). The results of scanning electron microscopy (SEM) tests are consistent with those of the UCS tests and leaching tests. The microcosmic mechanism of the changes in engineering of the stabilized contaminated soils under wetting and drying cycles is revealed.