Mining Contract: Structural Analysis and Design of Seals for Coal Mine Safety
This contract will transfer protective structure design technology from the defense establishment to the design and construction of seals in the coal industry. Researchers at the Engineer Research and Development Center (ERDC) will:
These tasks will be accomplished through the use of finite element analysis of typical seal designs under new explosion pressure requirements, and in close cooperation with testing accomplished by NIOSH at its Lake Lynn Laboratory.
Contract Status & Impact
Efforts to date on Task 1 have used two- and three-dimensional finite element methods for the analysis of coal mine seals. When possible, USACE used tests conducted at NIOSH's Lake Lynn Laboratory to validate the model calculations. The focus was on common seal types such as:
- reinforced concrete seals, both hitched and unhitched,
- plain concrete seals that are hitched,
- plain concrete plugs, and
- gob plugs with and without sealed ends.
USACE determined early in the project that, in addition to optimizing the design of the actual seal, one must also design an adequate foundation into the surrounding rock to support the seal. Three representative rock types were studied as foundation materials: Weathered Shale, Competent Shale, and Pittsburgh Coal.
Researchers investigated various options to connect the seal to the surrounding rock, such as rock bolts and rebar, and various types of hitching (into the ribs only, the floor only, or both). They examined how the required length of plug seal changes due to addition of hitching. USACE developed a simplified approach based on traditional bearing analysis to design the depth of hitching required to support a concrete seal, based on properties of in situ rock. For example, in weak weathered shale, a reinforced concrete seal survives the explosion load when the hitch depth is three feet, but fails with a one-foot-deep hitch.
USACE initiated Task 2, which will develop the mine seal analysis code based on the Wall Analysis Code. The new code is tentatively named WAC-MS. A beta version of the code can analyze seals as either flexural walls or plugs. The beta version also considers the seal foundation and whether it can provide sufficient restraint for the seal.
Under task 3, USACE conducted preliminary studies of the effectiveness of blast wave attenuators constructed of mine rubble piled nearly to the mine roof. These numerical studies examined the effect of different air gaps on the blast wave attenuation and showed that, as the size of the air gap increases, the degree of blast wave attenuation decreases. The simulations compared favorably to full-scale tests of blast wave attenuators conducted at NIOSH's Lake Lynn Laboratory.
Researchers at USACE have also completed work on task 4 to apply protective structure design principles to coal mine seals. Protective structure design principles require structures to fail in a gradual, ductile mode and not in a sudden, catastrophic mode, and should continue to provide some protection after the peak failure load is exceeded.
A final report describing all work performed by USACE is in progress and will be completed by October 2010.
Research under this project has resulted in the following publications:
- Computational Analysis of Mine Seals Designed to Resist Explosions
J. O'Daniel, W. McMahon, and B. Walker. Paper and presentation at 79th Shock and Vibration Symposium, Orlando, FL, October 26-30, 2008. Proceedings published March 2009.
- Protective Design Concepts Applied to Explosion Resistant Mine Seals
Bob E. Walker, Will McMahon, and James O'Daniel, paper and presentation at 79th Shock and Vibration Symposium, Orlando, FL, October 26-30, 2008. Proceedings published March 2009.
- Methane Explosion Modeling in the Sago Mine
W. McMahon and J.R. Britt, paper and presentation at Conference on Society of Mining, Metallurgy, and Exploration, Denver, CO February 22-25, 2009.
- Methane Explosion Modeling in the Sago Mine
W. McMahon and J.R. Britt, paper accepted for publication in SME Transactions, 2009.
- Use of Hitching for Mine Seals
J. O'Daniel, B. Walker and W. McMahon, Paper and presentation at 80th Shock and Vibration Symposium, San Diego, CA, October 25-29, 2009. Proceedings published March 2010.
- Wall Analysis Code for Mine Seals
D. Hyde, B. Walker and W. McMahon, Paper and presentation at 80th Shock and Vibration Symposium, San Diego, CA, October 25-29, 2009. Proceedings published March 2010.
- Calculations of Experiments of Mine Blast Attenuators Constructed of Rock Rubble
B Britt and M Sapko, Paper and presentation at 80th Shock and Vibration Symposium, San Diego, CA, October 25-29, 2009. Proceedings published March 2010.