Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Mining Engineering

First Advisor

Dr. Kyle A. Perry

Abstract

Continued depletion of easier coal reserves has necessitated development at deeper overburdens. At greater depth, operations often encounter more difficult ground conditions due to higher stresses and potential multiple seam interactions. Pillars which are left intact as the primary support mechanism experience an increase in loading. Mine design improvements are often incorporated to combat increased loads, principally by increasing pillar size. However, the potential for coal bumps, which are a rapid and violent failure of coal pillars, has increased due to these higher stresses and the use of larger width-to-height (W/H) ratio pillars.

Many efforts have been made to predict coal bumps; however, coal is a naturally occurring, inhomogeneous, and discontinuous geologic material. As a result, the best means for understanding coal pillar bursts are not efforts to predict the events themselves, but to advance knowledge of the associated environmental factors including geologic influences, stresses, and mining method. These factors have a tremendous impact on the loading distribution and resulting behavior of coal pillars. Of particular importance is the post-failure behavior of coal pillars which influences the mechanisms and functionality of pillar failure. Unfortunately, understanding of the post-failure behavior of squat coal pillars and the recognition of functional pillar strain has been limited.

The Ground Response Curve (GRC) has traditionally been used to evaluate the behavior of rock mass to the mining process by comparing the ground response/convergence curve to the support (e.g. pillars) response curve. The GRC has been employed in an effort to improve understanding of squat coal pillar behavior for numerous case studies with varying geologic and geometric conditions. The relationship between the GRC and individual pillar deformation has been examined using numerical modeling techniques. Using these widely accepted methods, a range of typical coal geologies and mining geometries was investigated, seeking to establish relationships between pillar performance, energy release, and the resulting mode of failure. The physical and dynamic properties of the rock and rock mass for coal and surrounding strata, geometric considerations, and pillar interface properties have been determined to be important indicators of squat coal pillar behavior and ultimately bump potential. As a result, new understanding of post-failure ground response has been developed and improvements have been made towards enhanced classification of mine-specific bump criteria, or bump “red zones”.

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