Mining Project: Detecting and Managing Dynamic Failure of Near-Seam Features in Coal and Nonmetal Mines

Principal Investigator	Heather Lawson - Request information
Start Date	10/1/2015
Objective	To develop strategies for identifying and managing geologic features that increase the risk of dynamic failures in underground coal deposits.
Topic Area	Ground Control Overview

Research Summary

Dynamic failures, also termed “bumps,” “bounces,” and “bursts,” can be defined as the violent ejection of coal into a mine opening [Peng, 2008]. Dynamic failure generally occurs suddenly, with little or no warning, and, based on data from MSHA’s Mine Data Retrieval System, results in worker injury up to and including death in 60% of reported cases. Despite evolving mining techniques and practices, these events continue to occur. Between 1983 and 2013, there were nearly 400 cases of reportable dynamic failure accidents in coal and nonmetal mines, resulting in 20 deaths, 155 lost-time accidents, and an estimated 48,000 lost man hours. The identification and mitigation of dynamic failure hazards remains a clear and present need.

Following the Crandall Canyon coal mine collapse, NIOSH made research recommendations to Congress regarding dynamic failures in deep room and pillar mines [NIOSH 2010]. In the analysis leading up to these recommendations, the important roles of specific geologic features and their spatial variation in heightening these risks were clearly acknowledged. The recommendations include advancing the science and understanding of dynamic failures so that criteria for identifying significantly elevated risk can be established. Criteria focused on variable geology and stress were specifically singled out for scrutiny in future research investigations. While the recommendations specifically targeted coal bumps associated with deep room and pillar mining, the roles of geologic features in concentrating stresses, and their interplay with mine layouts, are clearly relevant to dynamic failures under other mining conditions as well.

Investigations of coal bumps over the past 80 years have shown that the risk of dynamic failure can be related to the combined influence of deep cover, mine layout, the presence of stiff, laterally continuous, strong strata in the roof or the floor, and/or the presence of mechanically-significant sandstone channels. Mark et al. [2012] recently reported on a detailed investigation of a 15-year history of bumping in one deep western US coal mining district. A majority of the 34 dynamic failures investigated occurred in mines with pillar designs that were felt to be sufficiently robust to have provided adequate support to the overburden. To explain why these bursts had occurred, despite the pillars satisfying design guidelines, a strong association with geologic structures was argued to be evident in the majority of cases. Sudden failure of strong members in the floor was speculated to be responsible for some of these events, whereas faults were suggested to play a role in others.

The take-away lesson from these studies is that it is essential to understand the roles that geology plays in structural response, so that mine designs can tolerate the variable deformation response associated with variable material/geologic properties. However, in practice, numerical models used in formulating mine designs in the year 2015 do not explicitly account for site-specific variations in geologic features because local variations are poorly identified or totally unknown ahead of mining. Exploration drilling is inadequate to provide the resolution required to identify local variations in geology. A significant increase in pre-mining geological data by drilling/geophysics is needed for detection of likely anomalous geology.

Identifying the parameters of critical attributes of potentially hazardous geologic features, such as strength, thickness, etc., and their proximity to the seam represents a significant step toward targeting and designing effective mitigation procedures. This project seeks to identify near-seam geologic features that produce dynamic failures and abnormal ground deformation in underground mines through detailed geologic characterization, monitoring, geophysical techniques, and site-specific numerical modelling. It further seeks to provide mine operators with concisely defined strategies for both identifying and subsequently ameliorating these hazards, while minimizing worker exposure. Identifying the critical characteristics of near-seam features associated with dynamic failure events, within the framework of the larger geologic and mining environment, will allow operators to identify specific hazardous geologic conditions during the exploration phase of mining, long before any worker exposure or risk. A full understanding of hazard location and characteristics will also provide a foundation for developing measures to control or remove the hazard.

To  contribute to this need for understanding of hazard location and characteristics, this project has five research aims, as follows:

1. Create a database of near-seam dynamic failure events which includes geologic conditions, mine design, and intensity of consequences (i.e. fatality, injury, lost production, etc.) of the failure.
2. Create a holistic, three-dimensional geologic model of the collaborating mine site.
3. Devise an exploration methodology for the identification and locations of potentially hazardous features.
4. Monitor selected areas where potentially hazardous geologic conditions may exist in order to create additional case study information, improve model predictions, and evaluate exploration techniques.
5. Propose and evaluate mitigation techniques that can eliminate or ameliorate identified hazards.

The impact of this project research will be measured by the implementation of the suggested practices by the mining industry. This impact will be reflected in two ways: The first will be a cultural shift toward more proactive hazard control; the second will be a reduction in the occurrence of dynamic failure events following the implementation of the suggested procedures.

References

 Mark C, Phillipson S, Tyrna P, Gauna M [2012]. Characteristics of Coal Bursts in the North Fork Valley of the Gunnison River Valley, Colorado. In: Proceedings of the 31st International Conference on Ground Control in Mining. Morgantown, WV.

NIOSH [2010]. Research Report On Coal Pillar Recovery Under Deep Cover.

Peng SS [2008]. Coal Mine Ground Control. 3rd Ed. Morgantown, WV: Department of Mining Engineering, West Virginia University, 750 pp.

Related Conference Paper

Lawson HE, Weakley A, Miller A [2015]. Dynamic Failure in Coal Seams: Implications of Coal Composition for Bump Susceptibility. In: Proceedings of the 34th International Conference on Ground Control in Mining. Morgantown, WV.

 

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