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ANALYSIS OF PORE STRUCTURE BASED SWRC PREDICTING MODELS IN CHARACTERIZING CHEMICAL EFFECTS ON SWRC OF COMPACTED BENTONITE
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摘要: 在高放废弃物深地质处置库复杂的地下水环境影响下，缓冲/回填材料微观孔隙结构的改变通常会大大影响其水力性质。为探究这种影响，众多学者从不同理论出发，建立了相应的土水特征模型。然而，针对这些模型的对比研究较少，且缺少将模型应用于考虑化学影响的情况。在压实膨润土微观结构分析的基础上，基于分形理论和双孔理论，分别构建了压实膨润土土水特征预测模型，然后基于不同浓度NaCl溶液处理后压实GMZ膨润土的压汞试验数据，用两种模型预测其土水特征曲线，并与实测曲线进行比较。研究结果表明：两种模型均适用于预测化学溶液作用下压实膨润土的土水特征曲线；经历干湿循环使压实膨润土孔径趋于均一，导致其土水特征曲线为单峰形式，试样的持水作用由小孔主导，故相较于双孔持水的实测试样，预测试样在低吸力范围内持水能力较低；与蒸馏水处理后相比，盐溶液导致集聚体间孔隙减少，在相同基质吸力下试样的含水量降低；而在高浓度盐溶液处理后，由于孔隙流体通道增加和压实膨润土内部产生微裂隙，试样在高吸力范围内的持水性略有增强。Abstract: During the long-term operation of deep geological repository of high-level radiational waste, the chemical environment causes changes to the pore structure of the buffer/backfill material, which can affect the material's hydro-mechanical properties. Under the foundation of fractal theory and dual-porosity theory, we establish two pore structure based SWRC predicting models to study the feasibility of the two theories to connect the microstructure with hydraulic properties of compacted betonite considering chemical effects. The pore size distribution data of compacted GMZ bentonite treated with different concentrations of NaCl solution is obtained by mercury intrusion method. The SWRCs of the samples are predicted through the established models and compared with the measured curves. Results show that the predicted SWRCs tend to be the same as the measured SWRCs in the higher range of matric suction. However, compared with the dual-porosity of the SWRC testing specimen, only the intra-aggregate pores control the water retention capacity of the compacted bentonite after the wetting and drying process. Therefore, the predicted SWRCs show single peak and the established models don't perform well in the lower suction range. Compared with the distilled water treatment, the salt solution leads to the decrease of inter-aggregate porosity and the decrease of water content under the same matric suction. However, with the treatment of more concentrated salt solution, the water retention capacity of the specimen increases slightly in the range of high suction due to the increase of pore fluid channels and the formation of micro-cracks in the compacted bentonite.
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图 1 考虑压实膨润土双孔结构的SWRC
Figure 1. The double-peak SWRC considering the dual-porosity structure of compacted bentonite
图 2 膨润土微观结构示意图(修自Nasir et al.(2017))
Figure 2. The microstructure of bentonite(modified from Nasir et al.(2017))
图 3 压实GMZ膨润土(ρd=1.7 Mg ·m-3)的孔径密度曲线(He et al., 2016)
Figure 3. The pore size density curve of compacted GMZ bentonite(ρd=1.7 Mg ·m-3)(He et al., 2016)
图 4 压实GMZ膨润土(ρd=1.7 Mg ·m-3)的累计压汞曲线(He et al., 2016)
Figure 4. The pore size cumulative curve of compacted GMZ bentonite(ρd=1.7 Mg ·m-3)(He et al., 2016)
图 5 基于He et al.(2016)孔径分布数据预测的压实GMZ01膨润土SWRC
Figure 5. Predicted SWRCs according to the pore size distribution data from He et al.(2016)
表 1 分形模型参数
Table 1. Parameters of the fractal model
参数 DWS110 C0.1S110 C1.0S110 e(试验求得) 0.67838 0.63973 0.62477 Gs(试验给出) 2.66 2.66 2.66 β(拟合参数) 0.43768 0.83013 1 ψAEV(由孔径求得)/MPa-1 2.304 2.326 0.641 D(拟合参数) 2.84334 2.92321 2.95016 R2 0.98098 0.98044 0.62477 
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表 2 双孔模型参数
Table 2. Parameters of the dual-porosity model
参数 DWS110 C0.1S110 C1.0S110 em(试验求得) 0.65063 0.61198 0.53249 e(试验求得) 0.67838 0.63973 0.62477 Gs(试验给出) 2.66 2.66 2.66 αom(拟合参数)/MPa-1 0.17318 0.14358 0.35903 αoM(拟合参数)/MPa-1 8.55×1041 4.167×1041 8.053×1042 nm(拟合参数) 1.25065 1.30729 1.31483 nM(拟合参数) 1.00325 1.00293 1.00092 mm(拟合参数) 0.200416 0.235059 0.239445 mM(拟合参数) 0.003239 0.002921 0.000919 R2 0.98186 0.98459 0.99516
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