混合型缓冲材料水分迁移及干缩开裂规律研究

Study on Moisture Transfer,Dry Shrinkage and Crack of Bentonite-sand Mixtures as Buffer/Backfill Material

膨润土砂混合物在高放射性废弃物地下填埋处置工程中有着广泛的应用,其在养护过程中对结构完整性、裂隙数量和变形尺寸都有着很高要求。为了研究掺砂率和厚度对混合型膨润土在干缩过程中的含水率变化及开裂规律的影响,本研究制备了不同掺砂率、厚度的试样进行室内恒温干燥试验,并对整个过程含水量进行连续监测。试验结果表明,增大试样厚度及适当提高掺砂率均有助于抑制膨润土收缩变形和开裂行为,试验得到试样最小裂隙率时的掺砂率范围为20%~30%;干燥过程中试样蒸发率受到进气值和土颗粒间气液接触面积变化的影响;试样干燥过程随厚度的增大而延长,而残余含水率随掺砂率的增大而降低;引入干燥系数k并对其研究发现,水分迁移速率与试样厚度呈负相关,与试样掺砂率呈正相关。

Bentonite-sand mixtures have wide applications in the disposal of highly radioactive waste.As a burial material of nuclear waste,there are stringent specification for quantity and size of cracks and its structural integrity during its maintenance process.In order to study the effect of sand content and sample thickness on dry shrinkage cracking behavior and water content of bentonite-sand mixtures during drying process,indoor temperature drying tests were conducted on samples with different sand content and thickness.Water content was monitored continuously throughout the whole process.The experimental results showed that thickening the thickness of the sample and appropriately increasing the sand mixing rate are both helpful to inhibit the shrinkage behavior of the bentonite and the cracking phenomenon during the shrinkage process.And within the range of 20%to 30%sand mixing rate,the minimum fissure ratio could appear.During the drying process,the evaporation rate is affected by the air-entry value and the continuous change of soil-air contact area.Thickening the thickness of the sample could prolong the drying process,and the residual water content could be reduced by increasing the sand content.The drying coefficient k was defined and discussed.It can be founded that the water translocation rate is negatively correlated with the thickness of samples,but positive correlated with sand content.