ACPS: Evaluating Single and Multiple Seam Stability in Coal Mining

Overview of ACPS Software (Analysis of Coal Pillar Stability) 

The Analysis of Coal Pillar Stability (ACPS) software, developed by the National Institute for Occupational Safety and Health (NIOSH), is a widely adopted tool for assessing coal pillar stability in room-and-pillar mining systems. It is used in both single and multiple seam evaluations, providing engineers and mine planners with a reliable method to minimize the risk of collapses, roof falls, and pillar failures. 

ACPS relies on empirical methods built from extensive mine data. Users enter parameters such as mining geometry, pillar size, depth of cover, and geological quality, and the program calculates a factor of safety (SF). For most designs, an SF of 1.30 or greater is considered acceptable. 

One of ACPS’s key features is its ability to model multiple seam mining. When seams are mined above or below an active seam, the program accounts for stress redistribution and interaction effects. Engineers input interburden thickness, seam thickness, gob width, seam positioning, and Coal Mine Roof Rating (CMRR) values to evaluate these influences. This makes the tool especially valuable in regions with layered mining activity. 

For layout design, ACPS allows entry of parameters such as entry height and width, crosscut spacing, number of entries, and pillar dimensions. From these, it calculates the extraction ratio and stability factor. The program provides immediate feedback, issuing color-coded warnings (red or yellow) if stability is at risk and suggesting adjustments such as increasing pillar size, modifying spacing, or adding supplemental support. 

Outputs include text reports and charts that illustrate factors like stability versus cover depth, stress distribution across pillars, and interburden effects. These visualizations support clear interpretation of results. 

Although powerful and user-friendly, ACPS is an empirical tool with limitations. It is best suited to conditions within the range of its database and does not fully account for irregular geology or complex three-dimensional seam geometries. 

Overall, ACPS remains a benchmark tool for coal pillar stability analysis. Free to use and easy to learn, it delivers quick, defensible results that support safe mine design and planning. While not a substitute for advanced numerical modeling, it provides reliable decision support and continues to be a critical resource for ensuring underground mine safety.

ACPS Tutorial Documentation 

Problem Statement 

This tutorial demonstrates the use of the Analysis of Coal Pillar Stability (ACPS) software to assess the stability of coal pillars under multiple seam mining conditions. The objective is to evaluate whether the design of a room-and-pillar system in an active seam is stable, considering the influence of previously mined underlying seams. The scenario focuses on a typical five-entry development layout with no retreat mining, incorporating parameters for multiple seam interaction. 

Input Parameters 

The following parameters were used for the development layout: 

- Entry height: 3 m 
- Depth of cover: 60 m 
- Crosscut angle: 90° 
- Entry width: 5 m 
- Crosscut spacing: 15 m 
- Number of entries: 5 
- Equal spacing for all entries (ctc entry spacing = 13m) 
- Multiple seam: Enabled 
- Advanced geometry: Disabled 
- Retreat mining: Disabled 
 
Multiple Seam Parameters: 
- CMRR: 45 
- Interburden thickness: 50 m 
- Seam thickness: 3 m 
- Width of Gob: 100 m 
- Vertical position: Active OVER previous 
- Remnant structure in previous seam: Gob Solid Layout 

Outcome of the Tutorial 

This tutorial guided the user through creating a new development scenario in ACPS, populating room-and-pillar geometry, activating the multiple seam settings, and running the analysis. The results indicate whether the designed pillars are stable given the multiple seam interaction, helping engineers determine if redesign or support measures are needed. Users also reviewed ACPS outputs such as stability factors and warnings to interpret the influence of past seam mining activities on the current layout.