Stress distribution and failure characteristics of a longwall panel floor with a negative gate pillar

To study stress distribution and failure characteristics of a longwall panel floor with a negative gate pillar，coupled finite and discrete element numerical modelling method was adopted to construct a FLAC-PFC coupling numerical model. Spatiotemporal evolution of floor stress distribution，failure characteristics and effect of caved rock accumulation on floor stress and failure were analyzed throughout the process from setup room excavation to compaction of caved rock in gob to roof strata settlement. Based on elastic mechanics，a mechanical floor model was established to derive failure depth. The results show that：(1) Asymmetric accumulation of caved rocks in gob and asymmetric collapse of roof result in asymmetry of stress and failure of floor. (2) A “bottleneck” structure is formed by asymmetric failure of the floor and rotary cave-in of key blocks of roof，which hinders the further asymmetric slip of gob rocks. (3) The floor stress distribution under the influence of asymmetric accumulation of gob rocks presents a spacial distribution of “large top and small bottom”. And the stress concentration on both sides of the gob increases first and then decreases over time，and the floor stress experiences a transition of “compressive-tensile-compressive”. (4) Numerical simulation，theoretical calculation and field measurement results verify the asymmetric characteristics of stress and failure of floor caused by asymmetric accumulation of gob rocks. The study serves to provide theoretical support and scientific basis for determining location of gob side entry and its surrounding rock control of future adjacent panel with a negative gate pillar. © 2023 Academia Sinica. All rights reserved.