高压实膨润土膨胀力预测研究

Prediction of Swelling Pressure for Compacted Bentonite

摘要:

作为高放射性核废物深地质处置库缓冲回填材料，高压实膨润土的膨胀力是其缓冲性能的关键指标.在详细阐述膨润土水化膨胀过程的基础上，系统总结了膨胀力的预测机理、理论模型及试验验证的最新研究成果.国内外学者主要基于扩散双电子层理论，建立了膨润土膨胀力的预测模型；通过室内试验，研究了初始干密度、初始含水率等因素对膨润土最终膨胀力的影响规律.理论模型与试验结果对比分析表明，现有模型对蒙脱石含量较高、初始干密度较大的膨润土拟合性较差.实际上，高压实膨润土的膨胀过程包括晶层膨胀和扩散层膨胀，而现有理论模型仅适用于膨润土扩散双电层膨胀阶段，无法涵盖膨润土晶层膨胀阶段.同时，现有理论模型仅适用于预测膨润土的最终膨胀力，难以反映出处置库长期运营期间环境变化所导致的膨胀力演化过程.

Abstract:

Compacted bentonite has been selected as the potential buffer/backfill materials for the deep geological repository of highlevel radioactive nuclear waste; consequently the swelling pressure of compacted bentonite is the key index of its buffering performance. Based on the swelling process of compacted bentonite, the swelling mechanism, prediction models, and experimental verification of swelling pressure were systematically summarized. The existing predication models of bentonite swelling pressure are mainly based on the diffused doublelayer (DDL) theory. The laboratory tests demonstrate the influences of dry density, initial water content, sand content, and other factors on the final swelling pressure of compacted bentonite. The comparison between the model predication and the experimental results shows that the existing models have less fitting to the compacted bentonite with higher montmorillonite content and higher initial dry density. In fact, the swelling process of compacted bentonite includes crystalline swelling and DDL swelling, but the predication models are only used for estimating the DDL swelling, which cannot very well describe the crystalline swelling. The existing prediction models are only applicable to estimating the final swelling pressure of bentonite, but it is difficult to reflect the evolution process of swelling pressure caused by environmental changes during the longterm operation of repository.