Liquefaction phenomena are of great importance to those concerned with the impounding of mining and quarrying wastes, especially when the waste materials themselves are used for embankment construction. In this respect the effect of particle shape reported by the Authors is of much interest.

At Durham University we have been investigating the liquefaction potential of both fine and coarse colliery discards during the past three years, using controlled load and cyclic triaxial tests (Taylor et al. 1978a, b).

The examples of stress paths shown in Fig. 1 relate to controlled load tests carried out on coarse discards and other weak-rock aggregates, together with a fine discard test result conducted in the same effective confining pressure range. Two different coarse discard types are represented: (a) strong, coal-rich, platey material from west Wales (path 1), and (b) much weaker material from Nottinghamshire with a high seatearth content (path 2). Non-slaked shale from above the Harvey seam in Co. Durham was made up to the same nominal grading as the west Wales discard; this rock aggregate is represented by stress paths 3 and 4. Stress path 5 is a seatearth specimen from below the Harvey Coal, its particle size distribution being similar to the Nottinghamshire discard. Also shown on Fig. 1 is a test result (path 6) for shaly (non-plastic) tailings from a lagoon at the same west Wales colliery location as material 1. For these tests the stress paths are drawn such that: P̄ =1/2(σ′1 + σ′3) and q =1/2(σ13); where σ1

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