Alkaline solutions have significant effects on the mineral composition and on the microstructure of bentonite; in relevant geoenvironmental engineering applications, therefore, the properties of bentonite buffer materials must be taken into consideration in the presence of alkaline solutions. The objective of the present study was to determine the effect of alkaline conditions on the swelling of bentonite mixed with sand. Bentonite-sand mixtures were soaked in a NaOH solution and allowed to react over prescribed periods of 6, 12, and 24 months. Swelling deformation tests were conducted on the alkali-treated bentonite-sand mixtures; the swelling of the mixtures decreased significantly with increased reaction time. The fractal ec-σ relationship (ec is void ratio of bentonite, σ is vertical stress) was employed to express the swelling characteristics of the alkali-treated mixtures, wherein the swelling coefficient decreased as the bentonite content was reduced. Dissolution traces over the clay surfaces degraded the microstructural phase, thereby slightly increasing the fractal dimension. At higher dosages of bentonite, the swelling of bentonite-sand mixtures always followed a similar ec-σ relationship as that found for bentonite alone. On the contrary, in the mixtures with a small bentonite content that surpassed the designated threshold pressure, the void ratio of clay in the mixtures deviated from the ec-σ curve due to the appearance of the sand skeleton. The bentonite content for a particular bentonite-sand mixture at which deviation from the ec-σ curve began was ~50%. This deviation was almost negligible at 50% initial bentonite content in the bentonite-sand mixtures; after treatment with NaOH solution, however, a pronounced deviation in the ec-σ curve was observed which was caused mainly by the decrease in the bentonite percentage. Finally, the vertical pressure threshold was also estimated using the ec-σ relation for bentonite-sand mixtures with small bentonite contents over a range of various alkaline solution reaction times.

中文翻译：

---

膨润土-砂混合物在碱性溶液中长期溶解后的膨胀

碱性溶液对膨润土的矿物成分和微观结构有显着影响；因此，在相关地质环境工程应用中，必须考虑膨润土缓冲材料在碱性溶液中的性能。本研究的目的是确定碱性条件对掺沙的膨润土膨胀的影响。将膨润土-砂混合物浸泡在 NaOH 溶液中，并使其在 6、12 和 24 个月的规定时间内反应。对碱处理过的膨润土-砂混合物进行了膨胀变形试验；混合物的溶胀随着反应时间的增加而显着降低。分形ec-σ关系（ec为膨润土空隙率，σ 是垂直应力）用来表示碱处理混合物的溶胀特性，其中溶胀系数随着膨润土含量的降低而降低。粘土表面的溶解痕迹使微结构相降解，从而略微增加了分形维数。在较高剂量的膨润土下，膨润土-砂混合物的膨胀始终遵循与单独膨润土相似的 ec-σ 关系。相反，在超过指定阈值压力的少量膨润土混合物中，由于砂骨架的出现，混合物中粘土的孔隙率偏离了ec-σ曲线。开始偏离 ec-σ 曲线的特定膨润土-砂混合物的膨润土含量约为 50%。在膨润土-砂混合物中初始膨润土含量为 50% 时，这种偏差几乎可以忽略不计；然而，在用 NaOH 溶液处理后，观察到 ec-σ 曲线的明显偏差，这主要是由于膨润土百分比的降低造成的。最后，还使用 ​​ec-σ 关系估算了在各种碱性溶液反应时间范围内具有小膨润土含量的膨润土-砂混合物的垂直压力阈值。