Mechanisms of support failure and prevention measures under double-layer room mining gobs – A case study: Shigetai coal mine

TLDR

Support failure frequently occurs during longwall undermining beneath two layers of room mining goaf in shallow, ultra‑close seam mining. The study aims to identify geological and technological factors causing support failure and to develop methods to mitigate these effects. The authors use lithology, composite beam theory, finite element simulation, tributary area theory, and dynamic modeling to analyze load distribution and develop a support pull‑out method combined with stope reinforcement and reduced mining height. Key block instability analysis identified two critical moments, with critical moment A bearing the highest dynamic load, leading to significant economic losses and safety hazards from main roof fracturing.

Abstract

In the practice of mining shallow buried ultra-close seams, support failure tends to occur during the process of longwall undermining beneath two layers of room mining goaf (TLRMG). In this paper, the factors causing support failure are summarized into geology and mining technology. Combining column lithology and composite beam theory, the key stratum of the rock strata is determined. A finite element numerical simulation is used to analyze the overlying load distribution rule of the main roof for different plane positions of the upper and lower room mining pillars. The tributary area theory (TAT) is adopted to analyze the vertical load distribution of each pillar, and dynamic models of coal pillar instability and main roof fracture are established. Through key block instability analysis, two critical moments are established, of which critical moment A has the greater dynamic load strength. Great economic losses and safety hazards are created by the dynamic load of the fracturing of the main roof. To reduce these negative effects, a method of pulling out supports is developed and two alternative measures for support failure prevention are proposed: reinforcing stope supports in conjunction with reducing mining height, or drilling ground holes to pre-split the main roof. Based on a comprehensive consideration of economic factors and the two categories of support failure causes, the method of reinforcing stope supports while reducing mining height was selected for use on the mining site.