The problem of the stability of tips and spoil heaps was brought to public attention with dramatic force in 1966 by the disaster at Aberfan, when a slide involving only some 140 000 yd3 of colliery rubbish resulted in the loss of 144 lives, 116 those of children mostly between the ages of 7 and 10. Not only to the public, but also to most professional engineers and geologists—even to those concerned with mining—it came as a problem to which they had given little, if any, serious attention; though the discussion on Knox's 1927 paper to the South Wales Institute of Engineers suggests that there was local awareness of the problem of tip stability.
This lack of attention is perhaps surprising when we look at the scale of the problem of the disposal of waste from mining, from industrial processes and power generation, and from domestic sources (Table 1). The total quantity is about 120 million tons per annum within the United Kingdom, of which the largest contribution, nearly 60 million tons, comes from the mining of coal. It is of interest to note that the quantity of colliery waste has risen from 7 million tons in 1930 to 60 million tons in 1970 as a result of mechanization, although the overall quantity of coal produced has decreased.† It is also very significant that of the 60 million tons, about 5 million tons are in the form of slurry or tailings.
If tipped in the form of a