Abstract

Coal mine bumps are a serious safety problem in coal mines and they are very hard to predict due to the poor understanding of the exact mechanics of this dynamic failure phenomena. However, previous research has demonstrated that the local mine stiffness (LMS) criterion is a promising approach for analyzing the possibility of violent pillar failure. Typically, the local mine stiffness calculation quantifies the loading stiffness of the surrounding rock mass and compares that to the stiffness of the support pillars in the post-failure range in order to determine if a pillar failure in the mine will occur in a stable or un-stable manner. If the loading stiffness is softer than the support stiffness, a dynamic failure can occur. With this knowledge ahead of time, mine engineers can modify the geometries and pillar sizes in the mine design to help eliminate violent pillar failure.

In this paper, the principles of the LMS criterion for evaluating stable versus unstable failure are reviewed. Then the mathematical techniques used to implement a LMS calculation into LaModel are presented. Next, a simple idealized model is used to demonstrate and quantify the effects of rock mass stiffness and mine geometry on the LMS calculated by LaModel. Then, an actual coal mine, pillar bump accident is back analyzed with the LaModel code with the recently implemented local mine stiffness calculation. The numerical model was initially calibrated to thoroughly match the observed mine failure, and then the local mine stiffness and post-failure pillar stiffness were calculated and compared. In this mine model, the mine stiffness steadily decreased to eventually match the pillar stiffness at the time of the observed violent failure. This case study demonstrated that the local mine stiffness criteria can be successfully calculated and applied, but the accuracy of the calculation is very dependent on accurate rock mass and pillar properties.

1. OVERVIEW

Pillar bumps are a longstanding ground control problem associated with coal mining. This kind of pillar failure has presented serious safety problems in the United States throughout the 20th century [1, 2]. In order to attack the problem of bumps, the local mine stiffness stability criterion has been recognized as a reasonable analysis approach and it provides a means to distinguish if the pillar will fail in a stable or unstable manner [3, 4].

Although this theoretical criterion has been well established for a long time, there are still significant gaps in our ability to accurately evaluate the stability of pillars with it due to the challenges of accurately determining the post-failure pillar stiffness and the local mine stiffness in a mining layout [2].

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