Analysis of temporal-spatial variations in rock mass mechanics around gateway excavations within thick coal seam mining

Abstract Choosing optimal excavation and support parameters for gateways in thick coal seams poses a significant challenge in mining engineering, as it requires striking a balance between efficient excavation and the effective stabilization of surrounding rock. This research examines the stability of heading faces in thick coal seams by developing a mechanical model for the roof and deriving an equation for roof deflection using the finite difference method. Numerical investigations using FLAC3D software were implemented to analyse the rock mass response under varying support systems and excavation methods. Key observations include the following: (i) rock mass stability exhibits strong correlation with ground stress characteristics whereby minimal deformations are observed when the primary horizontal stress component intersects the gateway longitudinal axis at 45°. (ii) Enhanced coal strength leads to lower roof and sidewall displacement. (iii) A higher number of horizontal slices in the top coal layer results in an increase in the plastic zone height. (iv) Wider roadways and greater unsupported roof distances are associated with increased roof subsidence. (v) Through field practice, reasonable selection of support and excavation parameters effectively reduces rock mass deformation, lateral convergence is a maximum of 28 mm, roof movement is no more than 44 mm, and floor displacement is negligible. The study and field test provide an important reference for improving the stability of roadway in thick coal seam.