Mechanical Characterization and Artificial Floor Design for Underhand Cut-And-Fill Mining in a Kaolinized Altered Orebody

Thin, steeply dipping orebodies hosted in kaolinized altered fault zones are difficult to mine safely because of weak rock mass integrity, water sensitivity, and limited self-supporting capacity. This study investigates the F20 ore-bearing altered structural zone at Changtai Mining and develops an artificial floor design for downward drift-and-fill mining. Engineering geological characterization, rock mass quality evaluation, mechanical analysis, and three-dimensional numerical simulation were combined to assess floor-bearing requirements and regional recovery stability. The results show that the wall rocks are grade III, whereas the ore-bearing altered zone is grade IV and represents the controlling weak component. For the preferred 3.5 m × 3.5 m drift, an equivalent artificial floor bearing thickness of about 1.0 m is required. Numerical evaluation indicates that supported drifts remain stable, but crosscut–drift intersections are the main deformation and damage concentration zones. A representative 0.5 m drift offset significantly weakens the load-transfer path of the floor–rock system. The proposed vertically aligned, short drift, rapid backfill scheme with a reinforced composite artificial floor provides a practical basis for safe recovery of weak kaolinized altered orebodies.