JUSTIFICATION OF THE INTEGRATED SUPPORT SCHEME FOR THE PORTAL OF AN INCLINED RAMP UNDER A COMBINED OPEN-PIT MINING SYSTEM

The article addresses the issues of improving the stability of the portal and the initial section of an inclined ramp constructed during the transition of an open pit to a combined mining system. It is in this zone that the effects of rock mass unloading, roof and sidewall instability, water inflow, as well as additional dynamic impacts caused by drilling-and-blasting operations and the movement of mine transport occur simultaneously. The aim of the study was to substantiate an integrated support scheme that ensures the early formation of a load-bearing rock mass contour, reduces deformations in the near-contour zone, and preserves technological compatibility with both drilling-and-blasting and mechanized excavation methods. The study was carried out on the basis of field observations, laboratory testing of concrete and injection materials, instrumental monitoring of deformations, and numerical modeling in the FLAC3D software environment. The proposed scheme includes the sequential application of a primary shotcrete layer, installation of advance inclined rock bolts along the excavation direction, arrangement of a staggered grid of injection anchors, concreting of a section at least 20 m long, and primary and control grouting after the concrete reaches 75% of its design strength. It was established that the application of this scheme ensures a 2.3-fold reduction in water inflow, a 1.8-fold decrease in roof deformations compared with the control section, and a reduction in the maximum calculated displacements from 42 to 12 mm when rock bolting and injection reinforcement are used jointly. The obtained results confirm the feasibility of applying a combined support system in unstable host rocks and make it possible to recommend it for practical implementation in the construction of inclined ramp portals.