Sealing performance of bentonite and bentonite/crushed rock borehole plugs
- Arizona Univ., Tucson, AZ (United States). Dept. of Mining and Geological Engineering
This study includes a systematic investigation of the sealing performance of bentonite and bentonite/crushed rock plugs. American Colloid C/S granular bentonite and crushed Apache Leap tuff have been mixed to prepare samples for laboratory flow testing. Bentonite weight percent and crushed tuff gradation are the major variables studied. The sealing performance assessments include high injection pressure flow tests, polyaxial flow tests, high temperature flow tests, and piping tests. The results indicate that a composition to yield a permeability lower than 5 {times} 10{sup {minus}8} cm/s would have at least 25% bentonite by weight mixed with well-graded crushed rock. Hydraulic properties of the mixture plugs may be highly anisotropic if significant particle segregation occurs during sample installation and compaction. Temperature has no significant effect on the sealing performance within the test range from room temperature to 600{degree}C. Piping damage to the sealing performance is small if the maximum hydraulic gradient does not exceed 120 and 280 for samples with a bentonite content of 25 and 35%, respectively. The hydraulic gradients above which flow of bentonite may take place are deemed critical. Analytical work includes the introduction of bentonite occupancy percentage and water content at saturation as two major parameters for plug design. A permeability model is developed for the prediction of permeability in clays, especially in view of the difficulties in obtaining this property experimentally. A piping model is derived based on plastic flow theory. This piping model permits the estimation of critical hydraulic gradients at which flow of bentonite takes place. The model can also be used to define the maximum allowable pore diameter of a protective filter layer.
- Research Organization:
- Nuclear Regulatory Commission, Washington, DC (United States). Div. of Regulatory Applications; Arizona Univ., Tucson, AZ (United States). Dept. of Mining and Geological Engineering
- Sponsoring Organization:
- Nuclear Regulatory Commission, Washington, DC (United States)
- OSTI ID:
- 140792
- Report Number(s):
- NUREG/CR--5685; ON: TI92019210
- Country of Publication:
- United States
- Language:
- English
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