Mechanical and microstructural evolution of solidified/stabilized heavy metal-contaminated soil under a hydro-chemical-mechanical coupling environment

Zhongping Yang, Keshan Zhang, Xuyong Li, Jiazhuo Chang, Shuang Yang, Chunhua Ran
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Abstract

The long-term effectiveness of Solidification/Stabilization (S/S) under realistic disposal scenarios is a common controversy of its application. This study sought to investigate the evolution of the mechanical properties and microstructure of Pb-Zn-Cd composite contaminated soil solidified/stabilized by cement and fly ash (CSCS) under a hydro-chemical-mechanical coupling environment (HCM). An HCM simulation system was developed to reproduce the simultaneous action of hydraulic, chemical, and stress environments on CSCS. The mechanical and microstructural evolution of CSCS under HCM was assessed using vertical settlement monitoring, unconfined compressive strength (UCS) test, computed tomography (CT), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The increasing environmental acidity induces an increase in vertical displacement and a decrease in UCS. The highest final settlement was 0.96 mm at pH 3 and a pressure of 250 kPa, which was 39.13% greater than the value at pH 5 and 7. The UCS decreased by 18.54% after 168 h of HCM treatment at pH 7, while the value reached 45.83% when the pH was lowered to 3. Seepage contributes to initial hydration as evidenced by an increase in the early E50 of the CSCS. Hydrodynamic scouring and chemical erosion increase the pore size and deteriorate the soil structure, whereas compaction helps to redistribute soil particles, thus improving the structural integrity and uniformity of the CSCS.

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水-化学-机械耦合环境下固化/稳定重金属污染土壤力学与微观结构演化
固化/稳定化(S/S)在实际处置场景下的长期有效性是其应用的一个常见争议。本研究旨在研究水-化学-力学耦合环境(HCM)下水泥-粉煤灰固化/稳定铅锌镉复合污染土壤(CSCS)力学性能和微观结构的演变。开发了一个HCM仿真系统来重现液压、化学和应力环境对CSCS的同时作用。采用垂直沉降监测、无侧限抗压强度(UCS)测试、计算机断层扫描(CT)、压汞孔隙度测定(MIP)、扫描电镜(SEM)和傅里叶变换红外光谱(FTIR)等方法,对HCM作用下CSCS的力学和微观结构演变进行了评价。环境酸度的增加导致垂直位移的增加和UCS的降低。pH值为3、压力为250 kPa时,最终沉降最大,为0.96 mm,比pH值为5、7时增大39.13%。在pH为7的条件下,HCM处理168 h后,UCS下降了18.54%,而当pH降至3时,UCS下降了45.83%。渗流对初始水化有一定的促进作用,这可以从CSCS早期E50的增加中得到证明。水动力冲刷和化学侵蚀增加了孔隙大小,破坏了土壤结构,而压实有助于土壤颗粒的重新分布,从而提高了CSCS的结构完整性和均匀性。
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