ASSESSMENT OF STRESS STATE OF UNDERMINED ROCK MASS AROUND STOPES IN INITIAL CUT LAYER
Numerical modeling has produced stress-strain patterns in surrounding rock mass around stopes in initial cut layer 25 of block 9 in Internatsionalny Mine, ALROSA. The room-and-pillar mining in the initial cut layer is implemented beyond the influence zone of stoping, at a depth of 1000 m, with three working stages. The stress concentration coefficients are determined in the roof and sidewall rocks of the stopes at different mining stages. The results allow predicting stability of stopes as a function of mining depth based on the ultimate compression strength developed in kimberlite. For the initial cut layer in the conditions under analysis, parameters of the post-limiting zones in surrounding rock mass around the stopes are pre-estimated using the Mohr-Coulomb criterion and experimentally found limit values of shear stresses. In order to improve stability of the second stage stopes, it is recommended to drive them sideways from the center. The authors report the in situ observation data on undermined ore strata subsidence according to the evidence of deep benchmark stations. The comparative assessment of calculation and in situ data shows conformity of the geomechanical model parameters with the actual behavior of rocks, which allows using the geomechanical model for reliable prediction of mining-induced alteration of stress state of mine structures. Based on the experimental and analytical research, and on the in situ observation data, it has been found that weakening zone originates in the ore body 46.5 away from the roof. Strains 3Ч10-3 induce no discontinuity in rock mass and can be used for predicting stability of underground openings in the course of stoping advance.