"The mechanical properties of the Bonneterre Formation dolostone are critical to the design of underground mine openings at Ozark Lead Company's Sweetwater Mine, southeast Missouri. Host rock strength and elastic moduli, as affected by carbonate facies and varying moisture conditions, can influence rock stability in this multi-horizon mine.
Lead and zinc sulfide ores occur throughout the 350 foot-thick Bonneterre formation found in the mining area. Orebodies are mined in all four carbonate facies of the Bonneterre, including the (1) micrite (mudstone/wackestone) and shale facies, (2) the oolitic (packstone/ grainstone) facies, (3) the digitate stromatolite (boundstone) facies, and (4) the planar stromatolite and burrowed lime mudstone facies.
Ninety-five core specimens obtained from exploration holes drilled in the mine area were stressed to failure uniaxially. Compressive strengths, elastic moduli, and Poisson's ratios were determined using specimens representing the range of carbonate facies and varying moisture conditions found in Ozark Lead Company's underground mine.
It was found that Bonneterre dolostone mechanical properties can be correlated with rock texture and composition. It was found that the compressive strengths of the wackestone and boundstone facies were 3565 psi to 4280 psi higher than the packstone/grainstone facies. This behavior is believed due to the relatively high amount of "sedimentary binding" typical of the wackestone and boundstone facies.
Young's modulus decreases for specimens which contain higher shale content. It was found that the relatively non-shaly planar stromatolite and packstone/grainstone facies have the highest Young's moduli. This behavior is believed due to increased axial deformation from shale compaction during loading.
Poisson's ratio was found to be essentially constant (0.25), independent of facies. In order for this to occur, while the axial deformation is increasing in the shalier specimens, the lateral strain must increase at one fourth the axial rate.
The air dried core samples were found to have the highest compressive strengths. This is believed due to pore pressure buildup in the moist specimens causing strength decreases by friction reduction along the failure plane.
Core sample strengths were found to increase at the intermediate moisture states between the 77 1/2% relative humidity and fully saturated conditions, although all these strengths were less than the air dried strengths. This is believed due to pore pressure buildup that supported the surrounding rock skeleton. The observed axial strain rates measured at the yield point were found to decrease with moisture content, an expected consequence. The skeletal support essentially redistributes the axial stress across the specimen cross sectional area allowing higher loads prior to failure.
The decreases in Young's moduli (measured at 50% ultimate strength) with increasing moisture content are believed due to increasing axial strain during loading. These axial strain increases are probably due to grain slippage caused by carbonate cement dissolution and/or decreased interfacial tension at the higher moisture contents. The hypothesized grain slippage occurred prior to pore pressure buildup.
Decreases in Poisson's ratio with increasing moisture content are also believed due to axial strain increases brought on by grain slippage"--Abstract pp. ii-iii
Donald L. Warner
Charles J. Haas
John D. Rockaway
Geosciences and Geological and Petroleum Engineering
M.S. in Geological Engineering
University of Missouri--Rolla
xiv, 164 pages
© 1987 Harvey Edwin Goodman, All rights reserved.
Thesis - Open Access
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Full-text not available: Request this publication directly from Missouri S&T Library or contact your local library.http://merlin.lib.umsystem.edu/record=b1957929~S5
Goodman, Harvey Edwin, "The mechanical properties of the Bonne Terre Formation dolostone according to carbonate facies and moisture conditions, Sweetwater Mine, Viburnum Trend, southeast Missouri" (1987). Masters Theses. 466.