摘要
在高放核废物处置库中,膨润土-砂混合物是一种可选的缓冲回填材料,掌握其在水-力耦合条件下的体变特征对正确评价处置库的长期安全性有重要意义。按照不同的石英砂掺量(0%~50%)配制了6组膨润土/砂混合物,依次进行了单轴侧限压缩、有荷膨胀(轴向应力为0.2 MPa)和饱和再压缩试验,获得了混合物在不同水-力路径下的变形特征,并着重分析了砂掺量的影响。结果表明:(1)膨润土-砂混合物的压缩性与掺砂量、饱和状态和密实度有关。在非饱和及密实度较低(ρ_d<1.7 g/cm^3)的条件下,混合物的压缩指数随砂掺量的增加近似线性减小;当混合物压缩到较高的密实度(ρ_d>1.7 g/cm^3)并且饱和后,压缩指数受掺砂量的影响不明显,但其值远小于非饱和及低密实度状态。(2)混合物的最终膨胀率随着掺砂量的增加呈指数减小,随膨润土有效干密度的增加而呈指数增加。掺砂量达到40%时,膨胀过程伴随有体积回落现象,且体积回落率随砂掺量的增加而加剧。(3)混合物在不同水-力路径中及不同砂掺量条件下呈现的体变差异性与膨润土和砂在试样中的分布状态及二者对土体骨架的主导作用有关,总体上,掺砂量越高或试样密实度越大,砂对体变的主导作用越强。(4)混合物的膨胀力随掺砂量的增加而减小,通过引入膨润土有效干密度参数,建立了混合物膨胀力与该参数间的指数定量关系,可对膨胀力进行预测,并从蒙脱石的体积变化率与质量分布率的角度进一步分析了混合物膨胀力的作用机制。
The bentonite/sand mixture is an optional buffer/backfill material in the geological disposal of high level nuclear waste. Understanding the volume change characteristics of this mixture under coupled hydro-mechanical condition is highly significant for evaluating the long-term safety of the repository. In this investigation, six groups of bentonite/sand mixtures were prepared with different contents of quartz sand, i.e. 0%, 10%, 20%, 30%, 40% and 50%. Then a series of experiments including uniaxial confined compression （to a final dry density of 1.7 Mg/m3）, saturation （under 0.2 MPa vertical pressure） and reloading tests was carried out in sequence. The volume change behavior of bentonite/sand mixtures was understood, in addition, the effect of sand content was also analyzed emphatically. It is found that： （1） The compression behaviour of mixture significantly depends on sand content, saturation state and density. As the mixture is unsaturated and at relative low dry density （Pd 〈1.7 g/cm3）, the compression index decreases linearly with increasing sand content. However, as the mixture is saturated and at relative high dry density （po 〈1.7 g/cm3）, the compression index of mixture is independent of sand content, and the corresponding value is much less than that at unsaturated and loose state. （2） The final swelling strain of the mixture decreases exponentially with increasing sand content, while increases exponentially with effective bentonite dry density. As the sand content in the mixture is higher than 40%, volume collapse can occur during saturation, and collapse extent is enhanced by increasing sand content. （3） The observed volume change characteristics of themixture under different hydro-mechanical conditions or at different sand contents are mainly related to the distribution of bentonite and sand in the mixture, and their dominant effect on soil skeleton. Generally, the higher sand content and higher density, the volume change behavior the mixture is more conditioned by sand. （4） The swelling pressure of mixture decreases with increasing sand content. A parameter terms as ＂effective bentonite dry density＂ is introduced to quantitatively describe the swelling pressure of the mixture, and an exponential relationship between these two parameters is developed which can be used to predict mixture swelling pressure. Moreover, the swelling mechanism of bentonite/sand mixture is further analyzed based on volume change ratio and mass distribution ratio of montmorillonite in the mixture. In conclusion, this work is a reference for the selection and performance optimization of buffer/backfill materials.
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2017年第4期1041-1051,1059,共12页
Rock and Soil Mechanics
基金
基金项目优秀青年科学基金(No.41322019)
国家自然学科基金(No.41572246)
岩土及地下工程教育部重点实验室(同济大学)开放基金项目(No.KLE-TJGE-B1105)
国家自然科学基金重点项目(No.41230636)
江苏省"青蓝工程"(2014)
中央高校基本科研业务费专项资金(2015)~~
关键词
核废物地质处置
膨润土-砂混合物
缓冲/回填材料
压缩性
膨胀性
膨胀力
nuclear waste disposal
bentonite-sand mixture
buffer/backfill material
compression behaviour
swelling behaviour
swelling pressure
