混合型缓冲回填材料非饱和水分扩散试验研究

设计了专门的浸水试验装置，测定了膨润土-石英砂混合物在非膨胀条件下吸水引起的水分分布及膨胀应力变化，研究了混合型缓冲回填材料非饱和水力学性质。试验结果表明，干密度约1.70 g/cmP3、掺砂率为30%的GMZ001膨润土-砂混合物的水分扩散系数与含水率的关系呈U型变化，即随着含水率增加，汽态水分扩散系数减小，液态水分扩散系数增大。根据理论推导建立非饱和导水率估算方程。计算发现，混合物的非饱和导水率随含水率的增大而增大。其中，汽态水分非饱和导水率先增大后略有减小，液态水非饱和导水率始终增大。试验发现，试样吸水后干密度趋于均匀化，试样内部不同位置的应力发展与水分迁移过程密切相关：渗入端的应力在入渗初期增长很快，随后减慢；渗出端的应力持续稳定增长；入渗96 h后，两端应力趋于一致。估算出的水分扩散系数及非饱和导水率，可用于评价混合型缓冲回填材料阻隔核素迁移安全性。

Unsaturated water diffusion in compacted bentonite-sand mixtures as a high level radioactive waste buffer by infiltration tests

A water infiltration apparatus is specially designed to study the unsaturated hydraulic properties of compacted bentonite-sand mixtures under unconfined condition by measuring the moisture distribution and the swelling pressure during capillary water infiltration.Experimental data show that the water diffusion coefficient is changed with the moisture content of the mixtures(dry density 1.70g/cm3,sand ratio 30%) in a U-shaped curve.It is found that,with the increasing water content,the water vapor diffusivity decreases but the liquid water diffusivity increases.A theoretical analysis is made to estimate the unsaturated hydraulic conductivity,which expresses a general increasing tendency with the increase of water content.With respect to water states,it is found that the unsaturated hydraulic conductivity of water vapor increases at low water content and then decreases,but the unsaturated hydraulic conductivity of liquid water increases continuously at the same time.After water infiltration,the compacted mixtures tended to uniform as judged by dry density.The progress of pressure monitored at different positions of the specimen is found to be closely related to water migration process.For example,the pressure at water inlet surface increased much more rapidly at earlier infiltration stage and then increased slowly.The pressure at water outlet surface,on the other hand,increased continuously.After 96 hours infiltration,the pressure at both surfaces became almost the same.The parameters derived from this experimental research,such as water diffusivity and unsaturated hydraulic conductivity,can be used for safety evaluation of buffer material to radioactive nuclides.