Fly ash utilization in soil-bentonite slurry trench cutoff walls

Miscellaneous · Sun Jan 01 00:00:00 EST 1989

OSTI ID:6918418

Bergstrom, W R

The addition of fly ash, derived from coal-fired power plants, can significantly reduce the hydraulic conductivity of soil-bentonite slurry trench backfill mixtures. This was demonstrated with the use of falling-head permeability tests on trial backfill mixtures. The addition of up to approximately 40% fly ash by weight caused a reduction in the hydraulic conductivity of these mixtures, apparently by reducing porosity and by increasing the mixture specific surface. The observed effects of fly ash were adequately modeled by the Kozeny-Carman function, except for mixtures containing medium sand and very little ash. A model for the ideal, homogeneous mixture of particulate solids was developed, based upon the statistical characteristics of linear combinations of random variables. Three index tests were chosen for use with this model and for examining the mixing behavior of sand-fly ash-bentonite mixtures. The selected index tests were for percent fines, cation exchange capacity, and loss-on-ignition. After characterizing the individual mixture components separately with each of the three index tests, the results were used to validate the linear combination mixture model against index test results on numerous trial mixtures. A relatively high ash content (30% versus 10%) and a relatively low moisture content (23% versus 28%) appeared to aid in the mixing process. For preliminary design purposes, an ash content of approximately 30% should be chosen for use in the backfill mixtures. If no native clay fines are present, up to 4% bentonite may be required to achieve a hydraulic conductivity of less than 1 x 10{sup {minus}7} cm/sec. The backfill should be prepared relatively stiff (slump of 2 to 4 inches) and a tumbling-type mixer such as a portable pug mill should be used.

• Research Organization: Michigan Univ., Ann Arbor, MI (USA)
• OSTI ID: 6918418
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
20 FOSSIL-FUELED POWER PLANTS
EMBANKMENTS
WASTE PRODUCT UTILIZATION
FLY ASH
BACKFILLING
BENTONITE
CLAYS
HYDRAULIC CONDUCTIVITY
MATHEMATICAL MODELS
MIXING
MIXTURES
MOISTURE
PERMEABILITY
POROSITY
QUANTITY RATIO
RECOMMENDATIONS
SOILS
AEROSOL WASTES
ASHES
DISPERSIONS
RESIDUES
WASTES
010800* - Coal
Lignite
& Peat- Waste Management
200200 - Fossil-Fueled Power Plants- Waste Management