Floor heave in longwall gateroads is a severe issue that affects the mining safety and efficiency. Researchers, however, have limited understanding on the floor heave mechanism because the deformation of the post-failure rocks in the floor is seldom considered previously. In this study, we developed a theoretical model using the strain energy theory to investigate the post-failure deformation of rocks. This model was validated before being implemented into a numerical modelling package, FLAC3D, for floor heave analysis. Based on a case study of a longwall entry employing stiff-yield pillar configuration, we observe that the massive floor heave occurs at the entry rib that takes less loads (yield pillar) and eventually propagates toward the other rib bearing significant amount of loads (stiff pillar). This observation sheds lights on the floor heave mechanism in longwall gateroads and has major implications on the control technologies for a safe and efficient longwall mining.