Mining Topic: Pillar Design

Pillar diagrams showing stress distribution.

What is the health and safety problem?

Adequate pillar design is fundamental to maintaining stable underground openings and to providing a safe work environment for underground mine workers.

What is the extent of the problem?

All underground mines that are in tabular deposits require pillars that must be designed to support the overburden. There are about 700 mines in the U.S. in these types of deposits.

How is OMSHR addressing the problem?

The Office of Mine Safety and Health Research (OMSHR) has developed guidelines and criteria for the design of longwall gateroad pillars and coal and limestone pillars used in retreat mining. These guidelines are to a large extent empirically derived and based on case histories of pillar performance from a number of mines. The case histories were incorporated into extensive databases that were then used to develop the guidelines based on the success or failure of the pillars in each case.

What are the significant findings?

The pillar design guidelines have been incorporated into software packages that can be used for the preliminary design of pillars for longwall gateroads and retreat mining in coal and in limestone mines. The software packages are:

• ALPS (Analysis of Longwall Pillar Stability) for longwall gateroad pillars in coal
• ARMPS (Analysis of Retreat Mining Pillar Stability) for retreat mining pillars
• S-Pillar, for limestone mine pillar design

What are the next steps?

Longwall pillar design under deep cover is being evaluated through the use of underground field sites and numerical modeling. The database for the design of longwall gateroad pillars is also being updated.

Noteworthy Publications & Products

• ALPS - Analysis of Longwall Pillar Stability (2012-10)
  Software for designing pillars for longwall mines
• Pillar and Roof Span Design Guidelines for Underground Stone Mines (2013-03)
  This document presents the results of research conducted by NIOSH in cooperation with participating underground stone mines to develop generally applicable guidelines for designing stable pillars and roof spans in stone mines.
• Pillar Strength in Underground Stone Mines in the United States (2012-08)
  Stone mines in the eastern and midwestern United States use the room-and-pillar method of mining to extract relatively flat-laying sedimentary formations. A survey of pillar performance was carried out to identify potential modes of instability.
• Proceedings: New Technology for Ground Control in Retreat Mining (2010-04)
  This proceedings volume contains papers presented at technology transfer seminars sponsored by the National Institute for Occupational Safety and Health (NIOSH) on New Technology for Ground Control in Retreat Mining.
• The Ground Response Curve, Pillar Loading and Pillar Failure in Coal Mines (2012-08)
  This paper makes use of numerical models to examine the interaction between typical pillar systems and the surrounding rock mass for weak and strong geological conditions at various spans and depths of cover.
• Toward Pillar Design To Prevent Collapse of Room-and-Pillar Mines (2012-08)
  Three alternative approaches to reduce the risk of catastrophic collapse are described: containment, prevention, and full-extraction. Without good data available on post-failure pillar behavior, containment and full-extraction are the safest.