Department of Geotechnical Engineering, College of civil engineering, Tongji University, Shanghai 200092, China.
Department of Geotechnical Engineering, College of civil engineering, Tongji University, Shanghai 200092, China; Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China.
J Contam Hydrol. 2020 Mar;230:103622. doi: 10.1016/j.jconhyd.2020.103622. Epub 2020 Feb 4.
During the long term operation of a disposal repository, gas will be inevitably generated. Determination of gas permeability of compacted bentonite is of great importance for the safety assessment of the engineered barrier system. In the present work, the steady-state and residual pressure methods were employed to determine the gas permeability of GaoMiaoZi (GMZ) bentonite with consideration of variations in liquid saturation, dry density and confining pressure. Results show that, gas migration in saturated GMZ bentonite was mainly controlled by diffusion with an effective gas permeability of 1E-23 m - 1E-25 m. While in unsaturated GMZ bentonite, significant gas flow rates could be observed, which increased stably with the increase of gas injection pressure. Klinkenberg effect was significant when gas flow through GMZ bentonite. The Klinkenberg corrected gas permeability decreased by 3.5-5.5 orders of magnitude as the liquid saturation increased from 10% to 70%. A decreasing magnitude of 1-2 orders in Klinkenberg corrected gas permeability was presented with the dry density increased from 1.5 Mg/m and 1.7 Mg/m. The Klinkenberg corrected gas permeability decreased by 0-1 orders of magnitude as the confining pressure increased from 3 MPa to 7 MPa. By using the accessible porosity, gas measured intrinsic permeability could be determined with values ranged between 1E-15 m to 4E-15 m, which was higher than the water measured one by 5 orders of magnitude. Additionally, a generalized power law was successfully adopted in this study to describe the evolution of gas relative permeability with the liquid saturation. Overall, the effective gas permeability, Klinkenberg corrected gas permeability, intrinsic and relative permeability determined in this study provided a comprehensive perspective to assess the buffering property of GMZ bentonite in multi-physical field coupling environment. The parameters obtained can be adopted in further simulation works for long-term safety analysis of the disposal repository from the viewpoint of gas migration.
在处置库的长期运行过程中，不可避免地会产生气体。压实膨润土气体渗透率的测定对于工程屏障系统的安全评估具有重要意义。本工作考虑了液体饱和度、干密度和围压的变化，采用稳态和残余压力法测定了高庙子膨润土的气体渗透率。结果表明，饱和高庙子膨润土中气体的迁移主要受扩散控制，有效气体渗透率为 1E-231E-25 m。而在非饱和高庙子膨润土中，观察到明显的气体流速，随着气体注入压力的增加而稳定增加。当气体流经高庙子膨润土时，克林肯伯格效应显著。当液体饱和度从 10%增加到 70%时，克林肯伯格校正后的气体渗透率降低了 3.5-5.5 个数量级。当干密度从 1.5 Mg/m 和 1.7 Mg/m 增加时，克林肯伯格校正后的气体渗透率降低了 1-2 个数量级。当围压从 3 MPa 增加到 7 MPa 时，克林肯伯格校正后的气体渗透率降低了 0-1 个数量级。利用可及孔隙度，可以确定气体的固有渗透率，其值在 1E-154E-15 m 之间，比水测渗透率高 5 个数量级。此外，本研究成功地采用了广义幂律来描述气体相对渗透率随液体饱和度的演化。总的来说，本研究中确定的有效气体渗透率、克林肯伯格校正气体渗透率、固有渗透率和相对渗透率为评估高庙子膨润土在多物理场耦合环境中的缓冲性能提供了全面的视角。从气体迁移的角度来看，获得的参数可应用于处置库长期安全分析的进一步模拟工作中。
