Fly ash suspensions are used in Polish underground coalmines for many years, mainly for filling of caved areas. Computation of required amount of waste is one of the most important problem. It depends on volume of voids between rocks within the cavings (inter-grain space) and other factors. The total amount of suspension which can be used is named »absorbability of cavings«. Results of model studies and technical tests realized for 38 longwalls applying caving method are presented in the paper.
