Determination of the Required Strength of Artificial Roof for the Underhand Cut-and-Fill Mine Using Field Measurements and Theoretical Analysis

For the underhand cut-and-fill mining method, to ensure safe and economic mining, a key issue is to correctly determine the required strength of the artificial roof made of cemented paste backfill (CPB). However, the determination of the required strength is typically based on historical experience and analytical beam formulas, resulting in the obtained required strength being unsuitable for the actual situation. Therefore, in order to determine the required strength of the CPB roof reasonably and accurately, field measurements based on sensors were proposed and carried out in the Jinchuan mine, and then formulas based on thick plate theory were derived to verify the measured results. The results show that the required strength obtained by field measurement is 0.325 MPa and that obtained by thick plate theory is 0.304 MPa, with an error of 6.78% between them, verifying the accuracy of the measurements. However, the strength standard currently used by Jinchuan is 0.59 MPa, which far exceeds the optimal strength and results in many additional, unnecessary expenses. To ensure economical mining, the span of the drift was enlarged from 5.0 m to 6.0 m based on the results of the actual measurements and the current production status of the mine. The measurements show that the maximum cumulative subsidence of the drift roof is 11.69 mm and the maximum convergence deformation of the sidewalls is 8.34 mm, which indicates that the stability of the span-enlarged drift is satisfactory. Meanwhile, enlarging the drift span allows for a 20% increase in production capacity per mining cycle. This field measurement method and theoretical analysis model can be used as an efficient guide to facilitate the design of underhand cut-and-fill mining.