The most important link in the process chain for creating waste-free technology at concentrating plants is to ensure the possibility of using tailings, where the bulk of non-metallic minerals, rare earth minerals or overburden is concentrated. Increasingly, mining enterprises store their waste, forming man-made deposits. Thus at present time, the development of section technogenic deposits containing tailings is becoming a pressing challenge. The characteristic feature of such deposits is the polydispersity of the developed material, which makes it difficult to determine the fragmentation index. Therefore, the objective of this paper is to study the influence of the grain size distribution of tailings on the fragmentation index during the formation of an technogenic deposit, wherein said index affects the performance of mining and transport equipment, as well as the safety of mining operations. This paper is prepared with the application of the method of mathematical analysis, as well as a laboratory method, including determination of the volume of the pore space by displacement of the liquid phase from a container with a polydisperse mixture and measuring of weight indicators. The polydisperse mixture is represented by a fraction of 0–0,2 mm, 0,2–0,8 mm, 0,8–2,0 mm, 2,0–4,0 mm. 4,0–8,0mm, 3,0–12,0mm. An analysis was made of the influence of 5 indicators on the loosening coefficient. As a result of the study, it was found that the main criterion affecting the loosening coefficient is the ratio of coarse to fine class in the mixture, and not the size of the weighted average particle in it, and the smaller this ratio, the lower the loosening coefficient approaches 1. Class 1 reception in subsequent calculations. The results obtained will become the basis for studying the loosening factor in the development of man-made deposits, represented by tailings, and require further improvement of the theoretical foundations and industrial use.