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Reclamation of Phosphatic Clay Waste Ponds by Capping. Volume 4: Piecewise Linear Computer Modeling of Large Strain Consolidation

02-030-063Final

Abstract

Fine-grained mining wastes represent a major disposal problem in the United States. In Florida, as a by-product of the phosphate beneficiation process, over 50 million tons (dry weight) of highly plastic waste clay slurry are produced each year and stored in waste disposal ponds. These waste clays have very poor settling characteristics, with required time of 10 to 20 years for any significant degree of consolidation depending upon pond depths and material parameters. For efficient pond management, containment area sizement and reclamation, the rate and magnitude of consolidation is of paramount importance. Since field monitoring is not practical due to the lengthy time span, centrifugal and computer modelling offer viable alternatives to evaluate these consolidation rates and magnitudes.

Several consolidation computer programs based on the Gibson, England, and Hussey (GEH) theory (1969), and a piecewise linear program based on a spatial representation of finite strain, have been developed. However, GEH programs cannot model non-homogeneous profiles and the piecewise linear program has difficulty modelling initial filling conditions. Furthermore, no multiple layer large strain consolidation model, either finite strain or piecewise linear, has been developed. These drawbacks limit the applicability of computer modelling. Since piecewise linear theory is simpler than GEH theory, and allows for non-homogeneous profiles, a large strain piecewise linear program was developed which allows for any filling scheme in single layer consolidation (UF-McGS) and a method of solution for piecewise linear multiple layer consolidation model is outlined.

Results indicate that the UF-McGS model has excellent agreement with GEH theory for quiescent consolidation, quiescent consolidation with surcharge, and continuous fill. Also, the UF-McGS model agreed with a closed form solution developed for homogeneous quiescent clays.

Reclamation of Phosphatic Clay Waste Ponds by Capping.
Other Volumes

FIPR Publication No. 02-030-056
Volume 1: Centrifugal Model Evaluation of Reclamation Schemes for Phosphatic Waste Clay Ponds. University of Florida. April, 1988.

FIPR Publication No. 02-030-061
Volume 2: Centrifugal Modeling of the Consolidation Behavior of Phosphatic Clay Mixed with Lime or Gypsum. University of Florida. April, 1988.

FIPR Publication No. 02-030-062
Volume 3: Evaluation of the Use of Geotextiles for Capping Phosphatic Waste Clay Ponds. University of Florida. April, 1988.

FIPR Publication No. 02-030-075
Volume 5: Centrifugal Model Evaluation of the Consolidation Behavior of Phosphatic Clays and Sand/Clay Mixes. University of Florida. March, 1989.

FIPR Publication No. 02-030-073
Volume 6: Consolidation Properties of Phosphatic Clays from Automated Slurry Consolidometer and Centrifugal Model Tests. University of Florida. February, 1989.