Methodology for determining the optimal parameters of a rock release trench in the combined mining system for gently dipping deposits

A specific feature of combined mining systems in conditions of flat deposits of medium thickness is the need to form an ore release trench from the interchamber pillar in the underlying rocks. The volume of the release trench is one of the main factors affecting the efficiency of the combined mining system. Reducing the slope angle and the height of the release trench, on the one hand, allows reducing operating costs for breaking, releasing and delivering ore, caving of overlying rocks, on the other hand, leads to deterioration in ore extraction indicators. Determining the optimal parameters of the release trench depending on the width of the interchamber pillar is an urgent scientific and technical task. To solve it, a methodology has been developed for assessing the efficiency and determining the optimal parameters of the rock release trench based on the profit criterion per 1 ton of the recovered balance reserves, including the established functional dependencies of ore extraction indicators and the operating costs for the main technological processes of ore mining on the thickness and the dip angle of the deposit, the width of the interchamber pillar, the slope angle and the height of the release trench. It has been established that the optimal slope angle and height of the release trench with an interchamber pillar width of 8–18 m are 65° and 4.8–16.1 m, with a width of 18–20 m – 60° and 13.2–15.1 m, respectively.