Nature of Non-Recoverable Porosity Changes in Experimentally Deformed Indiana Limestone and Yule Marble: ABSTRACT

Abstract

Cores of limestone and marble with porosities from 0.5% to 15% were experimentally deformed dry, at room temperature under confining pressures from 3.5 to 27.6 MPa. Deformations were documented by changes in porosity, permeability, and mercury-injection pressure measurements. Pore and fracture geometries and interrelations were preserved by epoxy impregnation. In Indiana limestone at axial loads to 95% of mean failure strength, no significant changes in porosity could be detected, although there was a significant increase in twinned grains around pores, and a slight increase in mercury-injection pressures. At loads to 90% of failure (1.2% axial strain of which 0.4% is non-recoverable), a slight change in recovery efficiency was produced. The significance of this change is uncertain. If real, it is probably the result of microcracking observed at grain boundaries. After failure, a direct relation seems to exist between bulk axial strain and porosity. The porosity increase seems to be entirely disseminated, as no major fracture was formed, though shear zones 1 to 2-mm wide characterized by twinning and grain rotation were noted. Failure was accompanied by widespread grain and pore-size reduction. Yule marble stressed at axial loads to 99% of mean failure strength showed no measurable change in porosity. Failure was accompanied by increase in porosity which showed a correlation to bulk axial strain. This increase in porosity is in the form of both major fractures and a general increase in intergranular pore widths from less than 1 µ (undeformed) to betw en 1 and 10 µ (deformed). End_of_Article - Last_Page 796------------