Controlling Crosscut Damage in Response to Excessive Levels of Horizontal Stress: Case Study at the Subtropolis Mine, Petersburg, OH

Abstract

The Subtropolis Mine is a room-and-pillar mine extracting the Vanport limestone near Petersburg, Ohio, at a depth of approximately 59.4 m (190 ft). In February of 2018, mine management began implementing a new layout to better control the negative effects of excessive levels of horizontal stress. Almost immediately, the conditions in the headings improved. Conversely, and as expected, stress-related damage concentrated within crosscuts. Over the last 18 months, the mine operator has diligently experimented with different techniques/methods to lessen the impact of the instabilities in the outby crosscuts. The range of controls used by the mine operator include angled crosscuts, crosscut offsets, increase distance between crosscuts, arched crosscuts, cable bolted crosscuts, altered blasting pattern, and windows. A window is used to resist roof deformation by leaving a strong brow of roof rock within the crosscuts. A window reduces the crosscut dimensions vertically and, in some applications, horizontally. With each application of engineering controls, conditions were monitored and analyzed using observational and measurement techniques. In every case, the advantages in ground conditions were weighed against its impacts to haulage, ventilation, and other mining considerations. This paper examines how each engineering control was implemented and assessed. All these controls are based on well-established geomechanics principles, but experience has shown that local modifications are needed to deal with the unique local conditions such as geology, mining method, mine equipment, and in situ stress conditions.