| Pillar bumps have long been hazards in room and pillar mines around the world. With mines going deeper, pillar bumps also pose a threat to the personnel and equipment in longwall mining. One of the pillar bump mechanisms states that two parameters control the occurrence of pillar bumps; these are the post-failure pillar stiffness and the local mine stiffness (LMS). The magnitudes of the two parameters control whether there is violent or controlled failure. Although the mechanism was proposed in the late 1960s, the application of the mechanism to general mining practice is still far away. One of the reasons for this is that it is difficult to determine LMS in complex mining configurations, with non-linear material properties.; In an effort to solve this problem, LMS for a specific pillar was defined and a non-linear three dimensional boundary element program based on the displacement discontinuity theory was modified, by the integration of Starfield's "perturbation method", to calculate LMS. The change of LMS with the advance of the longwall face, the various chain pillar configurations, varied coal behavior, and the different surrounding rock properties were investigated by a parametric numerical analysis. To estimate the post-failure stiffness, the post-failure stiffness data from laboratory and field were collected and studied, from which an upper boundary estimation of the post-failure stiffness was derived.; Based on the results of the numerical analysis on LMS and the post-failure stiffness study, a design methodology for longwall chain pillars under the bump-prone conditions was proposed. The application of the methodology was demonstrated by a case history back analysis, which included an interpretation of the field data, a numerical simulation of the field case, and a stability evaluation based on the proposed LMS concept.; The results obtained from the parametric studies and case history simulation showed that the modified program worked well, and LMS of specific locations can be monitored throughout the mining simulation. The calculated change of LMS combined with the post-failure stiffness estimation can give an indication of when, where and whether there will be violent pillar bumps during the panel recovery. The chain pillar design can be evaluated and modified accordingly. Eventually, this will improve the safety and lead to a more reasonable design for longwall mining. |
