Last data update: Jan 27, 2025. (Total: 48650 publications since 2009)
Records 1-4 (of 4 Records) |
Query Trace: Evanek N[original query] |
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An insight into limestone pillar stability in dipping environments using actual mine geometries
Rashed G , Slaker B , Evanek N . Min Metall Explor 2025 As stone mine operations continue to develop in more challenging conditions including inclined seams, more complex loading conditions and pillar geometries are generated. The main objective of this study is to gain more understanding about the effect of seam inclination on the strength, the loading path, deformation of sidewalls, and yield patterns of a stone pillar using numerical models. The modeled width-to-height (W/H) ratio of the pillars, the unconfined compressive strength of limestone material, in situ stress field, and roof interface were varied to consider their potential distribution across underground limestone mines in the United States. Two actual mine geometries, referred to as a-type and b-type, were modeled. In a-type mine geometry, the roof is dipping while the floor is flat, making one side of the pillar shorter than the other side. In b-type mine geometry, the roof and floor lines of pillars are dipping while the headings/crosscuts are flat. The intention is not to compare pillar stability in these mine geometries, but to show pillar response in different dipping environments because these environments are different in pillar size, shape, and extraction ratio. Numerical modeling results indicate that dip pillars have reduced strength compared to flat pillars. The shear strength between the pillar and the surrounding rock has an impact on dipping pillar response. Dipping pillars experience high shear stresses, highly non-uniform stress distributions, and asymmetric yield pattern with more yielding compared to flat pillars. All these reasons place dipping pillars, particularly those with a small width-to-height ratio (<1) at an elevated risk of instability. The yield pattern for a flat pillar is simple while it is complex for a dipping pillar and depends on numerous parameters such as the width-to-height ratio of the pillar and seam inclination. The down-dip side of dipping pillars experiences more outward normal displacement compared to the up-dip side, while it experiences less vertical displacement. The results of this study improve the understanding of pillar stability in dipping environments and advance the ultimate goal of reducing the risk of dipping pillar instability in underground stone mines. © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2025. |
Controlling crosscut damage in response to excessive levels of horizontal stress: Case study at the Subtropolis mine, Petersburg, OH
Evanek N , Iannacchione A , Miller T . Min Metall Explor 2021 38 (1) 645-653 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. |
LiDAR mapping of ground damage in a heading re-orientation case study
Evanek N , Slaker B , Iannacchione A , Miller T . Int J Min Sci Technol 2021 31 (1) 67-74 The Subtropolis Mine is a room-and-pillar mine extracting the Vanport limestone near Petersburg, Ohio, U.S. In February of 2018, mine management began implementing a heading re-orientation to better control the negative effects of excessive levels of horizontal stress. The conditions in the headings improved, but as expected, stress-related damage concentrated within crosscuts. The mine operator has worked to lessen the impact of the instabilities in the outby crosscuts by implementing several engineering controls. With the implementation of each control, conditions were monitored and analyzed using observational and measurement techniques including 3D LiDAR surveys. Since the heading re-orientation, several 3D LiDAR surveys have been conducted and analyzed by researchers from the National Institute for Occupational Safety and Health (NIOSH). This study examines (1) the characteristics of each 3D LiDAR survey, (2) the change in the detailed strata conditions in response to stress concentrations, and (3) the change detection techniques between 3D LiDAR surveys to assess entry stability. Ultimately, the 3D LiDAR surveys proved to be a useful tool for characterizing ground instability and assessing the effectiveness of the engineering controls used in the heading re-orientation at the Subtropolis Mine. |
Insights into the relationships among the roof, rib, floor, and pillars of underground coal mines
Klemetti TM , Van Dyke MA , Evanek N , Compton CC , Tulu IB . Min Metall Explor 2020 38 (1) 531-538 Ground control failures continue to be one of the leading causes of injuries and fatalities in underground coal mining. The roof, rib, floor, and pillars are four areas of potential ground failures that miners, engineers, and consultants are continually evaluating. Quite often, these four underground structures are evaluated independently. A recent push to consider them as a system and in a similar manner as design engineers evaluate mechanical systems has highlighted the need to fully understand the interrelationship among the roof, rib, floor, and pillar. This relationship combines the geometry of the mine layout, geological environment, installed support, and even the timing of the coal extraction. Several studies using field observations and instrumentation show that these relationships can be independent at times, while being dependent in other scenarios. Cases with good roof conditions while the rib and floor deteriorate are contrasted with cases where the roof, rib, and floor deteriorate at the same time. The presented cases in this study demonstrate the importance of understanding the geological environment and mine design to ensure that the proper support is installed. |
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