Intrusion process of bentonite-sand mixture and its model in rock fissures with consideration of lateral wall friction
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摘要: 高放废物处置库建设与运营期间，作为缓冲/回填材料的高压实膨润土-砂混合物侵入裂隙，在降低围岩渗透性的同时，会引起膨润土的流失与可能的核素外泄，危及处置库的运营安全。针对膨润土-砂混合物侵入围岩裂隙问题，开发试验装置，开展不同裂隙宽度（0.1，0.3，0.5，1.0 mm）情况下，不同含砂率（0%，15%和30%）的膨润土-砂混合试样（石英砂粒径为0.075～0.1 mm）的裂隙侵入试验；利用预先设置的高精度数字相机，定时拍摄膨润土混合物侵入过程，再借助ImageJ图像处理软件，获取侵入距离以及附属（石英、长石与方石英等）与非附属矿物（蒙脱石等）环宽度等参数；基于入侵过程中膨胀力与裂隙侧壁摩阻力发展过程分析，构建并验证考虑侧壁摩阻的围岩裂隙膨润土侵入模型。结果表明：静水条件下，裂隙中膨润土的侵入距离、非附属与附属矿物环宽度等均随裂隙大小的增大显著增大，随含砂率增大明显减小；侵入达到平衡（稳定）后，挤出口处膨润土干密度随裂隙宽度的增大而减小，但随试样含砂率的增大而增大；附属矿物环区的摩擦系数明显大于非附属矿物环区的摩擦系数，即附属矿物环对膨润土侵入过程具有更强的抑制作用；考虑侧壁摩阻的膨润土侵入模型计算值能够较好地模拟实测值。侵入试验与模型研究可为实际处置库中膨润土的侵入行为预测提供依据。Abstract: During the construction and long-term operation of a deep geological repository for disposal of high-level radioactive waste, compacted bentonite-sand mixture invades and fills into fissures in the surrounding rock formations. This intrusion reduces the permeability of the rock formations. Meanwhile, it also causes the loss of bentonite with possible leakage of nuclides, resulting in endangering the operation safety of the repository. Aiming at solving the problems related to bentonite intrusion into rock fissures, a test device is developed, and the intrusion tests are conducted on the bentonite-sand mixture specimens (quartz size: 0.075～0.1 mm) with different sand contents (0, 15% and 30%) into artificial fissures with different sizes (0.1, 0.3, 0.5 and 1.0 mm). The images are regularly captured by the high-precision digital camera during the intrusion process of bentonite mixture. Then, with an ImageJ image processing software, the parameters including the intrusion distance and width of the accessory-mineral (quartz, feldspar and cristobalite, etc.) and non-accessory mineral (montmorillonite, etc.) ring are obtained. According to the analyses on the development processes of swelling pressure and friction resistance along the inner side wall of the fissures during the invasion process, an intrusion model for the bentonite intrusion in the surrounding rock fissures considering the friction resistance of the inner wall is proposed and verified. The results show that the bentonite intrusion distance and the widths of non-accessory and accessory mineral rings in the fissures increase significantly with the increase of the fissure size, and decrease obviously with the increasing sand content. After the bentonite intrusion reaches its equilibrium (stability), the dry density at the extrusion outlet decreases with the increase of the fissure width and increases with the increase of sand content. The friction coefficient of the accessory mineral ring area is obviously larger than that of the non-accessory one, indicating that the accessory mineral ring has a stronger inhibitory effect on the bentonite intrusion process. The measured results can be well simulated by the proposed model for the bentonite intrusion with consideration of the inner side wall friction of fissures. The researches on the intrusion tests and model can provide a basis for predicting the intrusion behaviors of bentonite in the actual disposal repository.
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Keywords:
- bentonite /
- intrusion /
- host-rock fissure /
- accessory mineral ring /
- lateral wall friction /
- model
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图 3 不同裂隙宽度下侵入距离时程曲线(含砂率0%)
Figure 3. Evolutions of intrusion distance with time for test on fissures with different sizes (sand content 0%)
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图 4 不同裂隙宽度与含砂率下的侵入状态（60 d）
Figure 4. Intrusion states with different fissure sizes and sand contents (60 d)
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图 5 不同裂隙宽度下非附属矿物环宽度时程曲线(含砂率0%)
Figure 5. Evolution of non-accessory mineral ring width with time for tests on fissures with different sizes (sand content 0%)
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图 6 不同裂隙宽度下附属矿物环宽度时程曲线(含砂率0%)
Figure 6. Evolution of accessory mineral ring width with time for tests on fissures with different sizes (sand content 0%)
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图 7 不同含砂率试样的侵入距离时程曲线
Figure 7. Evolution of intrusion distance with time for specimens with different sand contents
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图 8 不同含砂率试样的非附属矿物环宽度时程曲线
Figure 8. Evolutions of non-accessory mineral ring width with time for specimens with different sand contents
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图 9 不同含砂率试样的附属矿物环宽度时程曲线
Figure 9. Evolution of accessory mineral ring width with time for specimens with different sand contents
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图 12 附属矿物环宽度与非附属矿物环宽度关系曲线
Figure 12. Relationship between accessory mineral ring width and non-accessory mineral ring width
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图 13 摩擦系数与含砂率之间关系曲线
Figure 13. Relationship between friction coefficient and sand content
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图 15 膨润土侵入距离与两区域摩擦系数之间关系
Figure 15. Relationship between intrusion distance of bentonite and two-region friction coefficient
参数 数值 Gs 2.66 pH 8.68～9.86 液限/% 276 塑限/% 37 总比表面积/(m2·g-1) 570 主要交换离子 /(mmol·g-1) Na+ (0.4336)，Ca2+ (0.2914)，
Mg2+ (0.1233)，K+ (0.0251)主要矿物 蒙脱石(75.4%)，石英(11.7%)，
长石(4.3%)，方石英(7.3%)
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表 2 实测挤出口附近试样干密度
(g/cm3) Table 2 Measured dry density at extrusion mouth of specimens
含砂率/% 裂隙宽度/mm 1.0 0.5 0.3 0.1 0 1.36 1.52 1.60 1.66 15 1.43 1.59 — — 30 1.50 1.65 — —
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表 3 挤出口处蒙脱石干密度
Table 3 Dry densities of montmorillonite at extrusion mouth
含砂率/% 裂隙宽度/mm 1.0 0.5 0.3 0.1 0 1.17 1.34 1.42 1.48 15 1.14 1.29 — — 30 1.08 1.23 — —
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