National Mineral Resources University — Mining University, Saint-Petersburg, Russia:

A. V. Streletskiy, Assistant at the Department of Mine and Underground Construction, Candidate of Engineering Sciences, streletski@yandex.ru
M. G. Popov, Assistant Professor, Candidate of Engineering Sciences

Having stated highly complicated ground conditions and hydrogeology of underground extraction of weak iron ore from Yakovlevskoe deposit, Kursk Magnetic Anomaly, using method of top-downward horizontal slicing with backfilling, the authors offer a set of technical and technological actions aimed to enhance safety and efficiency of drivage, support and backfilling under the earlier made backfill. For estimation of stress-strain state of surrounding rock mass and to substantiate actions aimed at stability of underground excavations, 3D finite element model is constructed, including a few stages: generation of in situ stress state of rocks; formation of protective bridge; drivage under the protective bridge with different cross sections of excavations and types of support. It is found that spalling of exposed ore in side walls is induced by the limit state of adjacent ore body, and shearing surface initiates on the ore and bridge contact 1.2 m away of a drive if it has rectangular cross-section and is oriented at an angle of 68°. The modeled limit state zone agrees with in situ data of monitoring in excavations driven under backfill. Shaping the excavation as a trapeze and supporting it with cuttable bolts reduces horizontal distortion of the excavation by 75% as compared with the unsupported rectangular cross-section drive. Based on the finite element modeling of stress-strain state in ore body under mining, the authors substantiate and recommend trapezoidal cross-section excavations (larger base of the trapezoid is the excavation roof), reinforcement of excavation side walls with cuttable bolts and certain sequence of stoping and backfilling using solidifying mixture. The developed set of actions is recommended for application in the framework of construction project stage II in Yakovlevsky iron ore mine with annual capacity of 4.5 Mt.

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