RAPID FAILURES OF COLLIERY SPOIL HEAPS IN THE SOUTH WALES COALFIELD

The exploitation of the South Wales Coalfield, particularly from the l ast quarter of the nineteenth century onward, was accompanied by numer ous instances of instability within spoil heaps and their foundation m aterials. Sudden failures which were sufficiently rapid to overwhelm p roperty and services and, in some instances, to threaten life, occurre d on at least twenty three occasions, details of which are provided. I t is believed that these included sixteen how slides, five debris slid es and two failures caused by outbursts of groundwater. At five sites, debris how was a secondary failure mechanism. The locations of these failures are mostly clustered in those parts of the coalfield with the highest relief and with the highest rainfall, although antecedent rai nfall conditions for the failures were variable. Most are shown to be associated with active tipping faces, but one flow slide is believed t o have occurred on a tip four years after its abandonment and an outbu rst failure on a tip fifteen years old. The occurrence of rapid failur es is shown to mirror the development of the coalfield but has ceased largely as a result of legislation to improve tipping practice, which was enacted following the Aberfan flow slide.