Nomograms to calculate stability in slate and granite spoil heaps

One of the main problems involved in the mining of slate and ornamental granite is the unavoidable generation of waste rock, which must be stored in spoil heaps under suitably integrated, secure and stable conditions. Our work here focuses on this last point. To study the risk of instability within spoil heaps we have analysed the performance of a wide number of models with regard to circular slope failure, taking into account the different degrees of compactness of the material, the characteristics of the material itself, the effect of water pressure and the geometry of the heap. From this analysis we obtained more than 300 safety criteria, which were then used to draw up a series of nomograms to allow us to determine the risk of sliding in any granite or slate spoil heap. Thus, nomograms prove themselves to be suitable, quick, easy-to-use tools for preliminary studies of new structures, for periodic analyses of existing structures and to investigate structures that are due to be modified. (Author) 24 refs.