高庙子膨润土已被选为我国高放核废物处置库基质材料, 研究其力学性能对处置库工程的设计有着重要意义. 处置库预选区甘肃北山地区的地下水中盐溶解固体含量较高, 需要研究盐溶液作用下缓冲/回填材料的工程性质. 研究了高庙子钠基膨润土(GMZ07)及其掺砂率分别为0${\%}$, 30${\%}$ 和 50${\%}$ 的混合物在不同 NaCl 浓度下的强度特性, 并进行扫描电镜测试. 试验结果表明, 在纯水饱和条件下, 掺砂膨润土试样的应力应变曲线呈现明显的应变硬化, 但其峰值强度低于纯膨润土的峰值强度. 随着 NaCl 浓度的升高, 盐溶液饱和的掺砂混合物和纯膨润土的剪切强度均明显增大, 内摩擦角变大, 但黏聚力变化不大. 当 NaCl 浓度升高和坚向荷载增大时, 掺砂混合物的强度增加量明显高于纯膨润土, 并在 NaCl 浓度和压力较高的情况下, 掺砂混合物的强度大于纯膨润土的强度. 最后, 在掺砂混合物试样中引入膨润土有效干密度的概念, 并结合微观结构的分析, 解释了不同 NaCl 浓度下掺砂混合物的剪切机理.

Gaomiaozi (GMZ) bentonite has been identified as a potential buffer/backfill material for high-level radioactive nuclear waste (HLRW) repository in China. The mechanical behavior of buffer and backfill materials plays a significant role in the engineered barrier system of the HLRW repository. Beishan area is identified as the best candidate area of the national repository for HLRW, where ground water contains various dissolved chemical elements. Therefore, the effect of salt concentration on strength and microstructure of GMZ bentonite and its mixture with different sand ratios (0${\%}$, 30${\%}$ and 50${\%}$) was studied by performing a series of direct shear tests and scanning electron microscopy (SEM) examination. The results show that the stress-strain curve of the mixtures has noticeable strain-hardening, and the shear strength of pure bentonite is greater than that of the mixtures in pure water. The test results also show that shear strength of GMZ bentonite and its mixtures are noticeably improved with the increase of salt solution concentration. The friction angle is clearly increased with the salt solution concentration, but the cohesion intercept is not. The shear mechanism of the mixture can be explained by microstructure changes and the concept of effective bentonite density of specimens with different salt concentrations.