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|The strength of roof shales is, in part, a function of the preferred orientation of clay minerals within them. Therefore, analysis of clay fabric under both air-dried and hydrated conditions should be helpful in understanding roof shale failure. Core samples were collected from the Energy, Anna, and Lawson shales, which are locally present as roof shales of the Herrin No. 6 coal of southern Illinois. The Clay Fabric Index (CFI) was measured for thirty core samples, using X-ray diffractomtry, to investigate the relationship between clay fabric and roof collapse in coal mines. Greater CFI values indicate a weaker preferred orientation among clay minerals, which generally results in a weaker inter-grain bond. Average CFI values for air-dried samples were: 0.15 for Anna shale; 0.20 for Energy shale; and 0.37 for Lawson shale, .After the introduction of water, average CFI values increased to: 0.28 for Anna shale; 0.22 for Energy shale; and 0.43 for Lawson shale. The laboratory results indicate the following: [l] under air-dried conditions, Anna shale is the most stable, followed by Energy and Lawson shales; and 121 under hydrous (mine) conditions, Energy shale is the most stable, followed by Anna and Lawson shales. In mine environments where roof failures involving Energy shale have occurred, planar trends delineated by a relatively high density of small (0.2-4 cm diameter) iron concretions have been reported along the failure surface. Radial cracks have been observed around unsealed anchor bolt holes in the Anna shale. Instability of the Lawson shale is ubiquitous in coal mines. In the laboratory, similar physical changes were noted in the shale samples after the introduction of water, including [l] increased hydration around the perimeter of iron concretions in Energy shale,  radial extension cracks in Anna shale, and 131 extreme slaking of Lawson shale. Measured increases in the CFI reflect the observed physical changes of the samples upon the introduction of water, which probably reflect changes in strength that may result in roof failures in hydrated mine environments.|
Additional chapters/articles from the SME-ICGCM book Rock Mechanics as a Guide for Efficient Utilization of Natural Resources
|Rock Mechanics And Ground Control For Underground Mining And||Underground Storage, With Emphasis On Storage In Excavated R||Rock Classification For Portal Design||Laboratory And Field Characterization Of Immediate Floor Str||Comparative Study Of Western US Longwall Panel Entry Systems||Supercomputer Assisted Three-Dimensional Finite Element Anal||DEPOWS - A Powered Support Selection Model||A Study Of Displacement Field Of Main Roof In Longwall Minin||Cavability Investigation Of A Stratabound Copper Deposit, To||Influence Of Discontinuity Orientations And Strength On Cava||Premining Stability Analysis Of A Shaft Pillar At The Homest||Identification Of Critical Slope Failure Surfaces With Criti||Improving Design Methodology For Innovative Rock Mechanics D||Stability Evaluation Of Alternative Designs Of Drift-And-Fil||In Situ Stress For Underground Excavation Design In A Natura||Application Of Physical And Mathematical Modelling In Underg||Complex Seismic Trace Attributes In Coal Exploration||Changes In Seismic Measurements With Blast Induced Fracturin||Changes In The Seismic Properties Of The Cover Produced By L||Crosshole Seismics: Applications In Mining||Geotechnical Mapping By Seismic Imaging In Underground Mines||Experimental Study Of Line Electrode Method To Detect Underg||Time-Dependent Behavior Of Rocks: Laboratory Tests On Hollow||Pillar Sizing||An Applications Approach To Barrier Pillar Design For Improv||Yield Pillar Application Under Strong Roof And Strong Floor||Methods To Determine Pillar Stress Distribution And Its Effe||Correlation Between Unconfined Compressive And Point Load St||Study Of Coal Fragmentation Under Conical Bit Indentation||Development of in-situ stress measurement technique using ul||Understanding the hydraulic pressure cell||Development of a mechanistic model for prediction of maximum||Subsidence prediction using a laminated linear model||Subsidence and environmental impacts in Japanese coal mining||Surface damage due to longwall mining - A case study||Pre-mining stresses at some hard rock mines in the Canadian||Estimation of in-situ material strength||The research on the mechanical properties of hard roof in un||Relationship between the clay fabric of roof shales and roof||Failure mechanisms in ultra-close seam mining||An analysis of roof-pillar-weak floor interaction in partial||Finite element analysis and comparison of shaly mine roof su||Stability analysis and characterization of ground subsidence||Subsidence monitoring at a shallow partial extraction room-a||Assessment of surface fracture depth and intensity due to su||Prediction of surface movement with emphasis on horizontal d||Numerical simulation of coal pillar loading with the aid of||Three-dimensional FEM analysis to sale field measurements fr||Front abutment effects on supplemental support in predriven||Direct determination of failure surfaces in earth slopes||Hydraulic stowing - A solution for subsidence due to undergr||Research on the rational structure of tensible rockbolt and||System behavior analysis of the ground movement around a lon||CISPM - A subsidence prediction model||Dynamic rock anchors||Ropes mine crown pillar rock mechanics||Deformation and failure-time prediction in rock mechanics||Influence of joints on the elastic response of a LFUFL stope||Support selection of mine roadways by means of a computer pr||Theoretical analysis of breaking strength of mine pillars an||A comparison between two- and three-dimensional numerical mo|