2.5-dimensional Voronoi numerical simulation method for migration of direct roof in a longwall face

The fracture and migration patterns of direct roofs play a critical role in excavation stability and mining pressure. However, current methods fail to capture the irregular three-dimensional (3D) behavior of these roofs. In this study, the problem was solved by introducing an innovative 2.5-dimensional (2.5D) Voronoi numerical simulation method, dividing rock layers into 2.5D Voronoi blocks and developing cohesive element-based failure models, supported by a strain-softening Hoek–Brown model. The method was applied to the 8311 working face in the Taishan Mine in China, and its accuracy was confirmed through physical experiments. The following conclusions were drawn. The first roof break typically followed an “O-X″ pattern. The direct roof did not break randomly over time; instead, it followed three distinct scenarios: (1) A complete break of the direct roof occurred, followed by a sequential collapse (Scenario I). (2) Regional irregular stacking in one area was followed by sequential collapse in other zones (Scenario II). (3) The staged breakdown of the direct roof led to separate and sequential collapses on the left and right flanks (Scenario III). Scenario I was quite common during the 400 m advance of the working face and occurred five times. The fracture characteristics in Scenario I led to widespread pressure on the hydraulic supports in the middle of the working face. Finally, the direct roof from the working face towards the goaf area underwent phases of overhanging, hinging, and collapsing plates. After the first and periodic breaks, the basic roof formed stable hinged plate structures reinforced by overhanging plates and irregular accumulations of the direct roof.