this report reviews the use of unburnt colliery shale as mass-fill for road embankments since the issue of technical memorandum t4/68. it summarises data and observations obtained from engineers who have used the material during the past few years. in general all the engineers contacted considered that unburnt colliery shale formed sound embankments and provided excellent fill material with advantages over most soils particularly during periods of inclement weather. from a total of 12 contracts on which 3.9 million cubic metres of shale had been used there was no evidence of spontaneous combustion. it is suggested that with the use of modern compaction techniques spontaneous combustion is such a low risk that it can be discounted. in several cases the omission of the recommended layer of inert cladding (in addition to topsoiling) has not led to any difficulties and, as its inclusion sometimes introduces problems, the need for this requirement should now be reviewed. the restriction on height of shale embankments which some engineers have imposed appears to be unnecessary. there is a continuing risk of damage to concrete from sulphate attack when in close proximity to shale fill. special attention should still be directed to this point but if tests are carried out they should be on a modified basis. the scottish branch of the transport and road research laboratory will continue to collect and hold information on the use of unburnt shale from current and future contracts for the benefit of engineers who wish to enquire about experience elsewhere with this material. (a).

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