The National Coal Board, in seeking further outlets for using unburnt colliery shale, have considered that it could be a suitable fill material for reinforced earth structures although the Department of Transport regard it as being unsuitable for this particular purpose. The Report reviews the situation and identifies five areas of concern; these are the effects of (1) Acidity, sulphates and chlorides (2) Swelling (3) Heating (4) Variability and (5) Construction in wet weather. It is concluded that unburnt colliery shale should remain on the list of materials that are unsuitable for use in reinforced earth structures and that shale and mudstone should also be regarded as unsuitable. Attention is drawn to some of the problems that can arise from the use of pyrite-bearing shale and mudstone in general road construction.

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