Experimental Deformation of Pierre Shale.

The strength, mode of deformation, and induced pore pressure effects of Pierre Shale have been partially investigated at 20C, at confining pressures to 2 Kb, and at strain rates of 0.00001/sec to 0.0000001/sec. All tests were performed on cylindrical samples in which bedding was parallel to the axis of maximum compression. Dehydrated shale is about two and one-half times as strong as water-saturated shale. Application of stress to natural (water-saturated) shale creates transient pore pressures of significant magnitude. The measurement of, or control of, the induced pore pressure is one of the major experimental problems. Unconsolidated shale behaves brittly at all confining pressures. Consolidated shale is brittle below -200 bars, moderately brittle to -800 bars, and moderately ductile to ductile above -800 bars. Failure at confining pressure below -1000 bars occurs with the formation of sharply defined brittle faults.