It is known that mass explosion of ore by boreholes or mine charges under the system of forced storey collapse can be carried out on preformed compensation chambers or without them. The latter method - one-stage ore stripping in a clamped environment - is currently used at the apatite mine named after S. M. Kirov. S.M. Kirov apatite mine, Zapolyarny mine of Norilsk Combine, Salair mine, mine named after XXII Congress of the CPSU of Zyryanovsky Combine and others. The method of stripping affects the physical and mechanical properties of the stripped ore: if in variants with compensation chambers the coefficient of initial loosening of the ore immediately after blasting the block varies from 1.3 to 1.6, then at one-stage stripping this coefficient varies from 1.1 to 1.3.