多边界条件下缓冲/回填材料的膨胀特性

高放废物处置库中缓冲/回填材料的膨胀特性是评价其屏障性能的关键因素。受试验仪器等条件的限制,以往的膨胀试验基本都是在恒体积和恒应力这两种极端边界条件下开展的,无法有效反映处置库中的复杂应力–应变环境。研发了一套新型的多边界条件膨胀仪,集成了恒体积、恒应力和柔性等刚度3种边界条件。利用该膨胀仪对中国高庙子(GMZ)缓冲/回填材料开展了一系列膨胀试验,分析了边界条件对试样膨胀特性的影响。结果表明:研发的多边界条件膨胀仪具有操作简单、性能稳定等特点,能有效地模拟各种边界条件;边界条件对试样膨胀指标具有重要影响,对应的最终膨胀力关系为:恒体积柔性等刚度恒应力边界条件,最终膨胀率关系为:恒应力柔性等刚度恒体积边界条件;膨胀平衡极限(SEL)曲线可作为评价土体在复杂边界条件下水化时的最终体变和膨胀力的参考。研究结果对进一步认识土体的膨胀特性和指导高放废物处置库中缓冲/回填材料的设计具有一定参考意义。

Effects of boundary conditions on swelling behavior of buffer/backfill materials

The swelling behavior of buffer/backfill materials in high-level radioactive waste (HLW) repository is one of the significant indices evaluating their buffer/backfill properties. Due to the limitations of test apparatus, most of the previous swelling tests are performed under two simple extreme boundary conditions of constant volume (CV) and constant mean stress (CMS), which can not effectively reflect the complex stress-strain state in the repository. A new set of multi-boundary conditions dilatometer is designed to carry out a series of swelling tests under CV, CMS and constant stiffness (CS) boundary conditions. Based on this custom-made test apparatus, the swelling behavior of GMZ buffer/backfill materials is tested under complex boundary conditions. The results indicate that the developed test apparatus has the advantages of simple operation and stable performance, which can effectively stimulate various boundary conditions. The boundary conditions have an important influence on the ultimate swelling indices of samples. More specifically, the relationship between various boundary conditions and the corresponding swelling pressure is CV > CS > CMS, and the relationship between these conditions and the corresponding swelling strain is CMS > CS > CV. The swelling equilibrium limit (SEL) curve can be used as a reference for predicting the ultimate swelling strain and pressure of soils during hydration under complex boundary conditions. The test results have certain reference significance for further understanding the swelling behavior and guiding the design of buffer/backfill materials in HLW repository.