The effects of pore pressure on Berea Sandstone deformed at room temperature and 0 to 8000 psi effective confining pressure have been investigated. “Drained” tests, in which the applied pore pressure (μ0) is kept constant at a preselected level, and “undrained” tests, in which applied pore pressure (μ0) is allowed to fluctuate during loading, were conducted. Several tests were also conducted on air-dry specimens.
The drained tests show that the effective stress theory is applicable to Berea Sandstone, as suggested by previous investigators, and that wet specimens are approximately 11 percent weaker than air-dry specimens at all pressure levels. Peak strength (strength at failure) of an undrained test specimen is controlled by the effective confining pressure at failure (), and the magnitude of pore pressure rise in the specimen is governed by the initial effective confining pressure ().