Shear strength of stockpiled coking coal – Existing data

Flowslides and stability issues have occurred periodically within stockpiles of coking (metallurgical) coal at coal processing plants and export terminals in Queensland’s Bowen Basin, and to a lesser degree in New South Wales, since the early 1970s. A description of the issue and summary of research at James Cook University (JCU) from 1973 to 2000 was published in ACARP Report C4057 (Eckersley, 2000). Eckersley (2022) partly updated that work with SEEP/W transient seepage modelling of a 12 m high coal stockpile constructed at Hay Point in late 1991 for which initial moisture content, pore water pressures at the stockpile base, outflows from subsoil drains and final density and moisture profiles were measured. This provided a good starting point for modelling of moisture movements within production coal stockpiles as required for meaningful slope stability analyses. The current paper provides an accessible summary of available data from laboratory shear strength testing of coking coal to assist in selection and critical assessment of parameters for slope stability analyses of coal stockpiles. This includes data for saturated coal likely to form the base of a stockpile and currently limited data for unsaturated coal forming the bulk of a stockpile. It then highlights some issues in the selection of parameters for stability analyses of coal stockpiles.