Calculation of Temporary Roof Pillar Structure Parameters for a Novel Combined Mining Method

To tackle the technical challenges posed by mining steeply inclined thick ore bodies in deep mines, a combined mining method of roof pillar–induced caving and nonpillar sublevel caving was devised. One of the critical steps to ensure the successful implementation of the mining method is to determine the geometric parameter range of temporary roof pillars. The temporary roof pillars are conceptualized as a four-sided fixed support thick plate model, and stress analysis of the temporary roof pillar microelements is conducted to calculate the overlying load. Based on the fundamental equations of Reissner's thick plate theory, a functional relationship between the thickness of the temporary roof pillar and its ultimate length was derived. Taking the No. 37 experimental stope of the Daxin Manganese Mine as an example, an engineering case study was conducted to determine the geometric parameters of the temporary roof pillars in the trial stope. The results indicate that when the thickness of the temporary roof pillars is, respectively, set at 6, 7, 8, 9, 10, 11, 12, and 13 m, the corresponding values of the ultimate length are 29.957, 36.285, 42.814, 49.391, 55.896, 62.273, 68.478, and 74.494 m. Referring to the breaking pattern of roof pillars in similar mining areas at the same depth and considering the economic viability of overlying ore reserves and the characteristics of roof pillar–induced recovery processes, a comprehensive recommendation suggests a temporary roof pillar thickness of 10 m and an ultimate length of 55 m for the trial stope. In response to the computational results, a numerical model was established and numerical simulations were conducted according to the mining sequence, ensuring that the simulated results comply with standard specifications. The research findings provide a scientific basis for the technological revolution of mining methods for steeply inclined thick ore bodies in medium and deep depths.