高压实膨润土的非饱和渗透膨胀模型

Experimentally derived model for suction-induced permeability,swell and microstructure behaviour of unsaturated compacted bentonite

高放废弃物深地质处置库中,作为缓冲/回填材料的高压实膨润土的设计功能是,遇水吸湿导致土体膨胀变形,以密封高压实膨润土块体砌置时形成的块体与块体之间和块体与围岩之间的施工缝隙以及围岩中因处置库开挖卸载引起的裂缝,形成阻障围岩中地下水渗入内库引起核素迁移,与库内高放废物的辐射扩散的人工屏障。高压实膨润土在自由膨胀条件下的膨胀应变和非饱和渗透系数由渗透试验测得;孔隙比和吸力的关系由压汞试验测得。吸力和含水率的函数关系可由土-水特征曲线测试试验得到。因此,自由膨胀条件下膨润土的非饱和渗透膨胀模型由膨胀应变、非饱和渗透系数和孔隙比与吸力的函数关系建立。结果表明:渗透系数和体积应变都随吸力减小而增加,因为吸力减小会导致孔隙比增加。这一发现有助于设计高放废物的最终处置方案。

In the deep disposal of highly radioactive waste,the engineering barrier made by densely compacted bentonite is used to prevent the groundwater infiltrating and the radioactive waste diffusing;and the gap between the bedrock and nuclear waste canister can be filled up by the hydro swelling bentonite.The permeability and swelling behavior of bentonite are needed to be carefully studied.It is Gaomiaozi(GMZ) bentonie from China to be investigated here.A series of laboratory tests were conducted including test for determining water retention curve,permeability coefficient test in swelling condition and mercury;intrusion porosimetry(MIP) test after that.A mathematical model is established for the relationship among permeability,swelling volumetric strain,void ratio and suction of GMZ bentonite.Equations of the model indicate that the permeability coefficient and swelling volumetric strain increase with suction decrease.The reason is that the decrease of suction can cause the increase of void ratio of bentonite which will cause the increase of permeability coefficient.This discovery can facilitate the design of deep disposal of highly radioactive waste.