Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion
In Japan, as in other countries, bentonite-based buffer materials are expected to play roles in reducing stress from rock masses and mitigating nuclide migration in the geological disposal of high-level radioactive waste. These roles are achieved by ensuring buffer density and thickness based on the...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
The Japan Society of Mechanical Engineers
2020-04-01
|
| Series: | Mechanical Engineering Journal |
| Subjects: | |
| Online Access: | https://www.jstage.jst.go.jp/article/mej/7/3/7_19-00469/_pdf/-char/en |
| _version_ | 1818427498631790592 |
|---|---|
| author | Tomoko ISHII Masahiro KAWAKUBO Ichizo KOBAYASHI Yuichi NIIBORI |
| author_facet | Tomoko ISHII Masahiro KAWAKUBO Ichizo KOBAYASHI Yuichi NIIBORI |
| author_sort | Tomoko ISHII |
| collection | DOAJ |
| description | In Japan, as in other countries, bentonite-based buffer materials are expected to play roles in reducing stress from rock masses and mitigating nuclide migration in the geological disposal of high-level radioactive waste. These roles are achieved by ensuring buffer density and thickness based on the swelling characteristics of clay. However, in practical construction, we should also consider bentonite buffer piping erosion, a phenomenon in which the buffer surface is destroyed by groundwater flowing between the buffer and rock. Such piping erosion may be a serious issue for maintaining an engineered barrier for radioactive waste in the geological system. In this study, the dynamic behaviors of piping erosion were experimentally investigated. In the experiments, 500 mm φ × 600 mm height compacted bentonite specimens were placed in a cylindrical acrylic cell and distilled water was continuously injected at a flow rate of 0.1 L/min from the bottom and the side of the cell. The amount of bentonite that flowed out of the cell was measured by turbidity of the suspended clay in the drainage water. In the results, while the bentonite specimen swelled between about 10 and 20 days and attached to the inside wall of the cell, a dominant flow channel (piping) was observed between the swelled bentonite specimen and the inside wall of the cell. In addition, the relationship between the accumulated amounts of injected water and eroded bentonite showed a constant slope on double logarithmic plots. Such behaviors indicate that the shear stress due to water flow locally exceeded the swelled bentonite’s shear strength. Furthermore, the slopes were similar to those already reported from a test using a smaller size cell. These results suggest that piping erosion proceeds with a simple regularity and that piping erosion in actual-scale bentonite buffers can be predicted using small-scale data. |
| first_indexed | 2024-12-14T14:46:41Z |
| format | Article |
| id | doaj.art-fd13181984c34704aacbe025234dcc40 |
| institution | Directory Open Access Journal |
| issn | 2187-9745 |
| language | English |
| last_indexed | 2024-12-14T14:46:41Z |
| publishDate | 2020-04-01 |
| publisher | The Japan Society of Mechanical Engineers |
| record_format | Article |
| series | Mechanical Engineering Journal |
| spelling | doaj.art-fd13181984c34704aacbe025234dcc402022-12-21T22:57:16ZengThe Japan Society of Mechanical EngineersMechanical Engineering Journal2187-97452020-04-017319-0046919-0046910.1299/mej.19-00469mejExperimental approach for understanding the dynamic behaviors of bentonite buffer piping erosionTomoko ISHII0Masahiro KAWAKUBO1Ichizo KOBAYASHI2Yuichi NIIBORI3Radioactive Waste Management Funding and Research CenterRadioactive Waste Management Funding and Research CenterKajima CorporationGraduate School of Engineering, Tohoku UniversityIn Japan, as in other countries, bentonite-based buffer materials are expected to play roles in reducing stress from rock masses and mitigating nuclide migration in the geological disposal of high-level radioactive waste. These roles are achieved by ensuring buffer density and thickness based on the swelling characteristics of clay. However, in practical construction, we should also consider bentonite buffer piping erosion, a phenomenon in which the buffer surface is destroyed by groundwater flowing between the buffer and rock. Such piping erosion may be a serious issue for maintaining an engineered barrier for radioactive waste in the geological system. In this study, the dynamic behaviors of piping erosion were experimentally investigated. In the experiments, 500 mm φ × 600 mm height compacted bentonite specimens were placed in a cylindrical acrylic cell and distilled water was continuously injected at a flow rate of 0.1 L/min from the bottom and the side of the cell. The amount of bentonite that flowed out of the cell was measured by turbidity of the suspended clay in the drainage water. In the results, while the bentonite specimen swelled between about 10 and 20 days and attached to the inside wall of the cell, a dominant flow channel (piping) was observed between the swelled bentonite specimen and the inside wall of the cell. In addition, the relationship between the accumulated amounts of injected water and eroded bentonite showed a constant slope on double logarithmic plots. Such behaviors indicate that the shear stress due to water flow locally exceeded the swelled bentonite’s shear strength. Furthermore, the slopes were similar to those already reported from a test using a smaller size cell. These results suggest that piping erosion proceeds with a simple regularity and that piping erosion in actual-scale bentonite buffers can be predicted using small-scale data.https://www.jstage.jst.go.jp/article/mej/7/3/7_19-00469/_pdf/-char/enengineered barrierbuffer materialbentonitepipingerosionscale effect |
| spellingShingle | Tomoko ISHII Masahiro KAWAKUBO Ichizo KOBAYASHI Yuichi NIIBORI Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion Mechanical Engineering Journal engineered barrier buffer material bentonite piping erosion scale effect |
| title | Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| title_full | Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| title_fullStr | Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| title_full_unstemmed | Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| title_short | Experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| title_sort | experimental approach for understanding the dynamic behaviors of bentonite buffer piping erosion |
| topic | engineered barrier buffer material bentonite piping erosion scale effect |
| url | https://www.jstage.jst.go.jp/article/mej/7/3/7_19-00469/_pdf/-char/en |
| work_keys_str_mv | AT tomokoishii experimentalapproachforunderstandingthedynamicbehaviorsofbentonitebufferpipingerosion AT masahirokawakubo experimentalapproachforunderstandingthedynamicbehaviorsofbentonitebufferpipingerosion AT ichizokobayashi experimentalapproachforunderstandingthedynamicbehaviorsofbentonitebufferpipingerosion AT yuichiniibori experimentalapproachforunderstandingthedynamicbehaviorsofbentonitebufferpipingerosion |