ABSTRACT:

Roof failures in the longwall headgates mostly occur outby the T-junction area within the front abutment pressure zone. The roof in this area could fail in the form of cutters, sagging, or collapse. Although front abutment pressure, high horizontal stress, and adverse roof geology are primary risk factors that cause headgate roof failure, other mining factors such as panel orientation, pillar sizes, roof support and operational parameters also contribute to the instability of a headgate. To prevent headgate failure during longwall mining, it is important to understand the causes of roof falls, risk factors, and effective risk mitigation measures. This study is based on the headgate roof support experience in a longwall mine in the Pittsburgh seam. The occurrence of roof falls in two longwall panels and the geotechnical solutions are described in detail. Numerical modeling was conducted to investigate the effect of the longwall retreat direction on stress concentrations in the headgate. Causes and risks of roof falls in the longwall belt entry, and mitigation measures for roof-fall risks are discussed. Through diligent geologic reconnaissance, proper roof support design, and proactive risk management, roof falls in longwall headgates can be prevented.

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