Experimental investigation on prefabricated horizontal drain-based vacuum dewatering-solidification combined method for treatment of dredged slurry
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摘要: 疏浚淤泥的含水率高、渗透性低、压缩性高、承载力低，难以快速高效地处理和处置。对此，介绍了一种复合方法，即基于水平排水板的真空脱水-固化联合方法，简称PHDVDS，并通过模型试验研究了PHDVDS方法处理高含水率疏浚淤泥的脱水减量效果和加固效果。模型试验分别采用石灰激发高炉矿渣微粉和水泥为固化剂，并与单一真空脱水方法（无固化剂）和直接固化方法（无真空脱水，以水泥为固化剂）的处理效果进行了对比。在模型试验真空脱水阶段，监测了真空脱水量和淤泥体积变化，即减量效果；在真空脱水结束后，取固化土样进行养护并测试了不同养护龄期土样的无侧限抗压强度，并结合固化土微观结构（XRD、SEM和MIP试验）分析了PHDVDS方法的作用机理。结果表明，与单一真空脱水法和直接固化法相比，PHDVDS方法的脱水减量效果和加固效果均更加优越。仅2 d真空脱水后，PHDVDS比单一真空脱水法的减量效果提高了7%~43%；其固化土样60 d无侧限抗压强度比直接固化法增大了6~54倍。Abstract: The dredged slurry exhibits the characteristics of high water content, low permeability, high compressibility and low or negligible bearing capacity, and is difficult to be rapidly treated and disposed of. Aiming at this problem, a composite method, i.e., the combined method of prefabricated horizontal drain-based vacuum dewatering and solidification, abbreviated as PHDVDS, is introduced, and a series of model tests are carried out to investigate the volume reduction and reinforcement effects of the PHDVDS method, with lime-activated ground blast furnace slag (GGBS) and cement as the binder, respectively. The performance of PHDVDS method is compared with that of the pure vacuum dewatering method (no binder) and the pure solidification method (no vacuum dewatering, using cement as the binder). During the vacuum dewatering stage of the model tests, the mass of discharged water and the settlement, i.e., volume reduction, are monitored, after which the unconfined compressive strength (UCS) of soil samples at different curing ages is tested, and the development of UCS is analyzed from microstructural point of view by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results indicate that, compared with the pure vacuum dewatering method and pure solidification method, the PHDVDS method demonstrates significantly better volume reduction efficacy and significantly better reinforcement efficacy. For instance, the volume reduction by the PHDVDS method after two-day vacuum dewatering is 7%~43%, higher than that by the pure vacuum dewatering method. The 60-day UCS of the PHDVDS-treated soil is 6 times~54 times higher than that of the pure solidification method.
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图 5 不同处理方法的固化土样的无侧限抗压强度
Figure 5. Unconfined compressive strengths of soils solidified by different methods
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图 6 石灰/高炉矿渣微粉比例对固化土强度的影响
Figure 6. Effects of Ca(OH)2/GGBS ratio on strength of solidified soils
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图 11 不同固化土样的累积孔隙体积曲线
Figure 11. Curves of cumulative pore volume of different solidified soils
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图 12 不同固化土样的孔径分布密度
Figure 12. Pore-size distribution densities of different solidified soils
表 1 模型试验方案
Table 1 Program of model tests
组别 固化剂
类型固化剂掺量/% 石灰/高炉矿渣微粉/% 真空
荷载/kPaVSLG1 石灰-高炉矿渣微粉 10 5 -80 VSLG2 石灰-高炉矿渣微粉 10 10 -80 VSLG3 石灰-高炉矿渣微粉 10 20 -80 VSLG4 石灰-高炉矿渣微粉 10 40 -80 VSC 水泥 10 — -80 SC 水泥 10 — — VD — — — -80 
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表 2 土体渗透系数随时间的变化
Table 2 Variation of soil permeability with time
工况 渗透系数 k/(10-8 m·s-1) 0.5 d 1.5 d 2.5 d 3.5 d 4.5 d Aw = 0% 1.10 1.10 1.10 1.10 1.10 Aw = 10% 2.96 1.47 0.82 0.79 0.77
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