Swelling characteristics of Gaomiaozi bentonite and its prediction

Gaomiaozi （GMZ） bentonite has been chosen as a possible matrix material of buffers/backfills in the deep geological disposal to isolate the high-level radioactive waste （HLRW） in China. In the Gaomiaozi deposit area, calcium bentonite in the near surface zone and sodium bentonite in the deeper zone are observed. The swelling characteristics of GMZ sodium and calcium bentonites and their mixtures with sand wetted with distilled water were studied in the present work. The test results show that the relationship be- tween the void ratio and swelling pressure of compacted GMZ bentonite-sand mixtures at full saturation is independent of the initial conditions such as the initial dry density and water content, hut dependent on the ratio of bentonite to sand. An empirical method was accordingly proposed allowing the prediction of the swelling deformation and swelling pressure with different initial densities and bentonite-sand ratios when in saturated conditions. Finally, the swelling capacities of GMZ Na- and Ca-bentonites and Kunigel Na-bentonite are compared.

碱性溶液饱和高庙子钙基膨润土膨胀特性及预测

建设高放废物地质处置库需要大量混凝土,而放射性核素衰变释放的大量热量会加速水泥老化,产生的碱性孔隙水会对膨润土的缓冲性能产生不利影响。以高庙子(GMZ)钙基膨润土为试验材料,选用NaOH溶液模拟碱性孔隙水,利用自主研制的耐腐蚀固结仪,完成不同浓度和不同干密度下的膨胀力实验。结果表明,在相同浓度碱性溶液饱和后试样的最终膨胀力随初始干密度的增大而增大;初始干密度相同时,低浓度碱性溶液对膨润土膨胀力有强化作用,高浓度碱性溶液对膨润土膨胀力有弱化作用;在0.3、0.5、1.0 mol/L NaOH溶液环境下试样的膨胀力在达到最大值后会出现下降,膨胀力衰减的程度与溶液浓度有关而与干密度无关。通过X射线衍射试验(XRD)分析矿物成分和晶层间距得到,蒙脱石含量和方英石含量随碱溶液浓度升高而降低,长石含量随着碱溶液浓度升高而上升;NaOH溶液会使钙基膨润土钠化,钠化程度受溶液浓度影响。最后利用蒙脱石孔隙比的概念,对试样的蒙脱石孔隙比和最终膨胀力结果在双对数坐标系中线性拟合,给出预测碱性溶液饱和钙基膨润土膨胀力的表达式。