ICGCM Papers:
Fundamental Research Studies
 
 
Biaxial Horizontal Swelling Strains in West Virginia Coal Mine Roof Rocks in Response to Moisture Adsorption
32nd International Conference on Ground Control in Mining
Biaxial Horizontal Swelling Strains in West Virginia Coal Mine Roof Rocks in Response to Moisture Adsorption
by
Monte R Hieb, WV Office of Miners' Health, Safety, and Training, Oak Hill, United States
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[Conference] 32nd International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Fundamental Research Studies
[Author] Monte R Hieb, WV Office of Miners' Health, Safety, and Training, Oak Hill, United States
[Abstract] 
Key Conclusions:
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Preferential wetting of clay minerals along NE-trending moisture planes, related to a fold-parallel microfracture fabric of regional extent across West Virginia, is our best explanation for the systematic NW-oriented biaxial swelling strains observed. The testing methods used in this study are simple and inexpensive and the results offer insight into a regional mechanical fabric that imparts a dynamic, asymmetrical horizontal stress to moisture-sensitive coal mine roof rocks over time. Because a similar mechanical fabric appears in the Devonian shale, these findings may also have implications for shale gas developers in the Appalachian Basin challenged by rapid aperture closure rates along horizontally-drilled induced fracture networks in Devonian rocks like the Marcellus.
Key Findings:
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Biaxial swelling strains were exhibited in nearly all rocks tested, with maximum horizontal deformations appearing normally incident to the strike of regional geologic fold structures. This relationship persists as fold strike orientation varies across the study area. A connection with Alleghanian fold development and/or Post Alleghanian fold relaxation is suggested. Moisture-induced fractures along azimuths which are parallel to the regional geologic fold structure, ranging in size from hairline cracks to sample-destroying cracks, are orthogonal to the observed biaxial swelling strain direction. Deformations are most dramatic in shale rocks, but occurred in sandstones and siltstones as well.
Objective of the Paper:
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This paper summarizes these findings by describing the test methodology and results. Oriented slabs of coal mine roof rocks collected across West Virginia in the spring of 2012 were dry-sawed to size, air-dried to stability, then monitored for moisture changes and deformations in the horizontal plane for one wetting cycle, followed by one drying cycle.
Problem Statement:
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Study of moisture-induced swelling strains in Pennsylvanian rocks of the Appalachian Plateau in West Virginia reveals a 2:1 biaxial horizontal deformation oriented NW-SE.