Geomechanical situation is analyzed in mining the ore body of kimberlite pipe "International" during underground working of the experimental-industrial block. Split layer winning was accomplished using the room-and-pillar system with ore-breaking by continuous miner and solid stowing. When conducting second working, instrumental and visual observations were completed for the state of pillars and stopes. Results of observations are used to analyze changes in the stress strain state for secondary working development in the split layer. Analysis was made on the basis of numerical calculations of the stress state of the constructive elements (elements are performed by method of boundary singular equations). In-situ data allowed to estimate stress values in pillars and roof of stopes and to apply them as criteria in further analysis of block development conditions. Optimal parameters are obtained for the development system and conditions of accomplishing mining works in the undercutting layer.
Regularities are established for the stress state formation in sublevel cutting under conditions of additional development. This made it possible to determine optimal order of stope winning in the layer.
Kimberlite pipe "International" of the Joint-Stock Company ALROSA presents a vertical ore body with an oval-shaped cross-section (95 × 60 ÷ 70m in size). The upper part of the pipe up to the depth of 286 m is mined by the pit. Since 1999 underground mining of the deposit has been begun at the depth of approximately 700 - 800m. Resources are won by the layer system of mining, goaf space being filled with soliding mixtures.
Experimental-industrial block (EIB) No.6 90 m in high was won at first at the depth of 700 ÷ 790 m from the surface. To provide mine productivity, the block is separated in three sublevels each 25–30 m in high. Stoping operations in the block are with ore body splitting (layer No. 1) according to the room-and-pillar scheme by stopes 5 m × 5 m and breaking by continuous miner. Note that after winning and stowing of the first layer, cavings roof and its stratification.
Stains and stresses are measured. Visual observations are performed for the character and volumes of edges failure. These data are further used to analyze variations in geomechanical situation during development of stoping operations in the undercutting layer, conducted on the basis of numerical calculations of the stress state for the constructive elements of development system. The results obtained permitted to estimate admissible stress values in pillars and roof of the stoping and to apply them as criteria for the further analysis of mining conditions for EIB.
In calculations, vertical stresses acting at the depth of H in an intact massif, σ0Y = -yH, horizontal ones σ0 = -λγH, where γ is the specific rock weigh in the massif. For the conditions of the mine "International", lateral thrust coefficient λ. = 0.7.