Sealing performance assessments of bentonite and bentonite/crushed rock plugs
Bentonite and mixtures of bentonite and crushed rock are potential sealing materials for high level nuclear waste repositories. The materials have been used to form cap layers to reduce infiltration for mined waste tailings and can also be used to construct clay liners for municipal as well as industrial waste managements. American Colloid C/S granular dentonite and 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 an appropriate composition 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 negative effects on the sealing performance within the test range from room temperature to 60C. The piping damage to the sealing performance is small if the maximum hydraulic gradient does not exceed 120 and 280 for 25 and 35% bentonite content, 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 the plug design. A permeability model developed is useful for the prediction of permeability in clays. A piping model permits the estimation of critical hydraulic gradient allowed before the flow of bentonite takes place. It can also be used to define the maximum allowable pore diameter of a protective filter layer.
- Research Organization:
- Arizona Univ., Tucson, AZ (United States)
- OSTI ID:
- 138263
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
ANISOTROPY
BENTONITE
CLAYS
COMPACTING
FLOW MODELS
FORECASTING
HIGH-LEVEL RADIOACTIVE WASTES
HYDRAULIC CONDUCTIVITY
INDUSTRIAL WASTES
LINERS
MICROSTRUCTURE
MIXTURES
MOISTURE
MUNICIPAL WASTES
PERFORMANCE TESTING
PERMEABILITY
POROSITY
QUANTITY RATIO
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE FACILITIES
SANITARY LANDFILLS
SEALING MATERIALS
TAILINGS
TUFF
WATER SATURATION
WEIGHT
Yucca Mountain Project