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Coal Preparation

Moisture Changes and Stability Problems in Coal Stockpiles

Coal Preparation » General

Published: January 99Project Number: C4057

Get ReportAuthor: John Eckersley | James Cook University of North Queensland

This report summarises works conducted at James Cook University on moisture movements and stockpile stability, including the current understanding of factors leading to moisture movement, erosion, shallow surface slipping and deep seated flowslides in coal stockpiles.

The basic stability and moisture processes in coal stockpiles are described in detail to provide an understanding of the associated stockpile problems and to provide a framework for interpretation of the results of laboratory testing.

Results are presented for extensive laboratory physical testing of moisture and strength properties of five coal types. These products include one studied in detail during earlier BHP coal sponsored research, for which there is some history of moisture movements and instability. Two further coking products know to be prone to slumping, and one for which excess moisture and instability problems are virtually unknown, were subjected to a comparable range of laboratory strength and moisture testing.

During the course of the investigation a range of laboratory and field investigation methods were developed or modified. Details are presented in the report or its appendices where appropriate. Investigations into erosion and shallow sliding in coal stockpiles are also presented.

Two case histories are presented to further validate the study approach and illustrate the proposed investigation methodology. In one case, moisture redistribution and drainage was measured by stockpile instrumentation, and analyses of moisture movements are presented. The second case history describes slipping and flowslide development in an experimental stockpile and the associated slope stability analyses.

In practical terms, the investigation demonstrates that moisture and stability problems in coal stockpiles are generally associated with significant fines contents (generally more than 12% finer than 0.5mm). Significant moisture redistribution results where product moistures exceed a moisture threshold that may be assessed using column drainage tests. Stockpiles formed with low dry densities and where moisture redistribution and rainfall infiltration result in substantial water levels in the stockpile may be prone to dramatic collapse due to contractancy of the coal.

This final report draws together data and conclusions from a range of past and current investigations. The work is not comprehensive, but provides a sound overview and methodology for assessing the potential for moisture and stability problems in coal stockpiles.

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