Coal pillar size design and surrounding rock control techniques in deep longwall entry

Abstract

We combine experimental data, FLAC3D numerical simulation results, and on-site industrial tests to study the problem of coal pillar size design in longwall entry. The Zhaozhuang coal mine located in Changzhi City, Shanxi Province, China, is used as a case study. We use an inversion calculation of the double-yield constitutive model to improve the reliability of the simulation results. Calculated results are fitted using a theoretical value of the Salamon strength formula to obtain mechanical parameters of the rock mass in the goaf, which are used to numerically simulate its compaction-bearing characteristics. The stress distribution state and plastic zone failure characteristics of entry surrounding rock under different coal pillar widths during mining are obtained by numerical calculation. The results show that increased coal pillar size leads to a gradual shift of the peak stress from the solid coal side to the coal pillar side. Use of an 8-m coal pillar generates a lower stress environment and has sufficient bearing capacity to remain stable. Based on the results obtained here, we propose differentiated support techniques that address the differential deformation and stress distribution of surrounding rock both sides of the goaf-side entry. On-site industrial tests show that the proposed support technology effectively reduces the deformation variation and ensures safe entry use during servicing.