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膨润土具有遇水膨胀的特性,是高放核废料深地质处置库理想的缓冲回填材料。膨胀特性是其作为缓冲材料最重要的性能之一,同时受多方面因素的影响。本文以我国首选缓冲材料——高庙子膨润土为研究对象,以含水率和干密度为控制变量,以恒体积法为试验方法,研究了高压实高庙子膨润土的水化膨胀特性,采用压汞试验法(MIP)对膨润土微观结构进行了研究,并以此对水化膨胀特性进行了解释。膨胀力试验结果表明,高庙子膨润土的膨胀力发展形式和最大膨胀力均受试样含水率和干密度影响,干密度较小时,水化曲线呈明显的双峰结构,干密度较大时,水化曲线形态与含水率相关,随着含水率增大,双峰结构逐渐消失。MIP试验结果表明,高庙子膨润土的孔径分布同样受含水率和干密度影响,随着含水率和干密度降低,集合体间大孔隙体积增多。膨润土的水化膨胀曲线受集合体间大孔隙影响显著。大孔隙较多时,膨润土集合体能迅速膨胀形成临时结构,当膨胀力超过临时结构的极限荷载时发生坍塌,膨胀力回落,内部结构重组后继续水化达到最大膨胀力,因此其水化膨胀曲线呈明显的双峰结构。随着大孔隙量减少,水化膨胀曲线由双峰结构演变成一条平滑曲线。
Bentonite has the characteristics of swelling with water and is an ideal buffer backfill for the deep geological disposal of high-level nuclear waste. Dilatancy is one of the most important properties of cushioning materials and is influenced by many factors. Taking Gaomiaozi bentonite, the buffer material of our country as the research object, taking the moisture content and dry density as the control variables, this paper studied the hydration expansion characteristics of the high-pressure Shigongmiaozi bentonite by using the constant volume method. The microstructure of bentonite was studied by mercury intrusion porosimetry (MIP), and the swelling property of hydration was explained. The results of swelling force show that the development mode of expansion force and the maximum swelling force of Gaomiaozi bentonite are affected by the moisture content and dry density of the sample. When the dry density is small, the hydration curve shows a bimodal structure with a large dry density The hydration curve is related to the water content. As the moisture content increases, the bimodal structure gradually disappears. The MIP test results show that the pore size distribution of Gaomiaozi bentonite is also affected by water cut and dry density. With the decrease of water cut and dry density, the pore volume of aggregates increases. The hydration expansion curve of bentonite is significantly influenced by the macropores of aggregates. When there are many macropores, the bentonite aggregates can rapidly expand to form a temporary structure. When the expansion force exceeds the ultimate load of the temporary structure, the collapse occurs and the expansion force drops. After the internal structure is reorganized, the maximum expansion force continues to hydrate. Therefore, the hydration expansion curve Obvious bimodal structure. As the amount of macropores decreases, the hydration expansion curve evolves from a bimodal structure to a smooth curve.